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Chapter 2 : Structure of the Microsporidia

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Abstract:

Classification of microsporidia is based on life cycle and structural characters. This chapter describes the structure and application of specific techniques, which helps to determine an organism is a microsporidian. The cell was interpreted to be a uninucleate gamete destined for fusion with another such cell to restore by plasmogamy the diplokaryotic state of a meront. When the cells are covered by the electron-dense material, they are classified as sporonts, the initial stage of sporogony. Whether rightfully belongs to the genus or should be retained in its original genus, . The genus is monomorphic, and single nuclei occur in all life cycle stages. Especially in the case of microsporidia from water-dwelling invertebrate hosts, the spores bear ornamentations or mucous layers on their surfaces that can be used as taxonomic characters. The size of spores is an important structural character, but its exact recording is difficult, especially in microsporidia with very small spores. Measuring spores on photographs, made with a carefully calibrated microscope and photographic enlarger, is a suitable alternative if a special eyepiece or image analyzer is not available.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2

Key Concept Ranking

Rough Endoplasmic Reticulum
0.48504218
Endoplasmic Reticulum
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Microtubule Organizing Centers
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0.48504218
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Image of FIGURE 1
FIGURE 1

Shape and staining reactions of microsporidian spores. (A) Lighdy pyriform (); (B) horseshoe-shaped (); (C) spherical (); (D) rod-shaped (); (E) lageniform (); (F) dimorphic sporogony with pyriform free spores and ovoid octospores (arrowhead) (); (G) angular octospores (); (H) ovoid spore with prominent exospore projections (); (I) diplokaryon (); (J and K) live ovoid spores (); (L) coupled spores (); (M) tetraspores with prominent mucus production (); (N) PAS reaction stains spores in the “polar cap,” i.e., the polar sac-anchoring disk complex (arrowhead) (); (O) spores in stained smear (A, B, and E) SEM; (C) dark field; (D and J) interference phase contrast; (F to H, and K) phase contrast; (I and O) Giemsa stain; (L and M) India ink negative staining; (N) PAS. Scale bars: A, B, and E, 1 μm; C, D, F to H, 10 μm; I to 0,5 μm. Reprinted with permission from (A), (B and D), (E), (I), and (L to N). Abbreviations: d, diplokaryon, PV, posterior vacuole.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 2
FIGURE 2

Reproduction and spore morphs. (A) Merogony, sporogony, and mature spores (); (B) chain of diplokaryotic merozoites ( sp.); (C) two stages of plasmotomy (); (D) two stages of schizogony (); (E to G) spore morphs of sp. from the gypsy moth larvae. (E) first-generation spores for intertissue transmission; (F) -type binucleate spores for interhost transmission; (G) -like uninucleate spores for interhost transmission. (A, B, and D) Giemsa stain; (C) hematoxylin; (E) interference phase contrast; (F and G) phase contrast. Scale bars: A, C, and D to G, 10 μm; B, 5 μm. Reprinted with permission from . (A and D). Abbreviations: d, diplokaryon; MP, merogonial plasmodium; Nu, nucleus; SP, sporo-gonial plasmodium.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 3
FIGURE 3

Cytology of early stages. (A) Monokaryotic meronts (); (B) diplokaryotic sporonts (); (C to E) diplokaryotic sporont () with details of the zone of nuclear apposition (D) and nuclear periphery (E) (arrowheads indicate nuclear pores); (F) mitotic spindle exhibiting micro-tubules (arrowhead), spindle plaques, polar vesicles, and chromosomes (arrows) (); (G) two-layered spindle plaque (); (H) synaptonemal complex with lateral (arrows) and central (arrowhead) elements (); (I) synaptonemal polycomplex (arrowhead) (); (J) sporoblast exhibiting Golgi apparatus, primordial anchoring apparatus, and polar filament (). (A and B) Giemsa stain, (C to J) TEM. Scale bars: A to C and J, 1 μm; D, E, and H, 100 nm; F, G, and 1,0.5 μm. Reprinted with permission from (A), (B to F), , and (I). Abbreviations: d, diplokaryon; f, polar filament; g, Golgi apparatus; m, mitotic spindle plaque; Nu, nucleus; Nc, nucleolus; Ps, polar sac; V, polar vesicle.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 4
FIGURE 4

Ultrastructure of the mature spore. (A) Longitudinally sectioned spore exhibiting the characteristic organelles (arrowhead indicates vacuolar membrane) (); (B) polyribosomes attached to membranes (); (C) circularly arranged polyribosomes () .TEM was used for all panels. Scale bars: A, 0.5 μm; B and C, 100 nm. Reprinted with permission from . (A), (B),and (C). Abbreviations: A, anchoring disk;E,endospore; EX, exospore; f, polar filament; Nu, nucleus; Pa, anterior polaroplast; Pm, plasma membrane; Pp, posterior polaroplast; Ps, polar sac; Pv, posterior vacuole; R, polyribosomes.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 5
FIGURE 5

(A) Schematic representation of the construction of a microsporidian spore (). (B) Schematic representation of the anterior part of the spore. (C) Schematic representation of the spore germination: polar filament eversion (a and b), passage of the spore contents (sporoplasm) through the lumen of the everted polar tube (c), and exit of the sporoplasm in the form of a minute cell at the tip of the everted polar tube (d). Modified with permission from Berrebi (1978) (A to C). Abbreviations: A, anchoring disk; E, endospore; EX, exospore; F, polar filament; FW, polar filament wall; N, nucleus; PA, anterior (lamellar) polaroplast; PP, posterior (vesicular) polaroplast; PV, posterior vacuole; PS, polar sac; R, endoplasmic reticulum with (poly)ribosomes.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 6
FIGURE 6

From sporoplasm to early sporogony. (A) Sporoplasm (); (B and C) meronts and sporonts (); (D) diplokaryotic meront (); (E) sporont with electron-dense material (arrows) accumulating spotwise (arrowhead indicates concentric layers of endoplasmic reticulum) (); (F and G) strandlike initiation of the exospore (arrowheads) (); (H) wide initiation of the exospore (arrowheads) (); (I) paramural bodies (arrowheads) ( sp. ex ). (A and D to I)TEM; (B and C) Giemsa stain. Scale bars: B, C, and 1,1 μm; A, D, and E, 0.5 μm; F to H, 100 nm. Reprinted with permission from E.Weidner (A), (B, C, and E), (F and G), and . (H).Abbreviations: d, diplokaryon; Nu, nucleus.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 7
FIGURE 7

(A) Schematic representation of the formation of the extrusion apparatus during sporont-to-spore transition (). (a) A small vacuole (ve) and Golgi vesicles (G) assemble close to the nucleus; (b) the polar sac primordium (PS) and a large vacuole appear close to the nucleus, and the Golgi (G) abuts the PS; (c) coils of the polar filament (F) start to form by coalescence of Golgi vesicles; (d) the polar sac and polar filament material start to be organized into layers; (e) the polar sac migrates toward the tip of the forming spore, and the polaroplast with both parts (PA, PP) appears. (B) Schematic representation of the spindle plaque of microsporidia (). The plaque (an MTOC) is situated in a depression of nuclear membrane (M) and consists of a stack of flattened electron-lucent vesicles surrounded by dense granular material from which microtubules (MT) radiate. Several vesicles (VE) are situated close to the plaque on its cytoplasmic side. Modified with permission from Vinckier (1973) (A) and (B).

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 8
FIGURE 8

Initiation of the extrusion apparatus and ejection. (A) Initiation of the polar filament and polar sac (). Note the close association of the sac with the nucleus. (B to D) polar sac and anchoring disk in sporoblast (B), immature spore (C), and mature spore (D). (B and D) ; (C) . (E) Polar filament seen in situ in one spore and ejected in the other ( sp. ex sp.). (F) Polar sac and anchoring disk during formation (). Note the layering of the nascent anchoring disk (arrow) and the presence of layered material to which the walls of the polar filament (arrowhead) abut. This structure serves as a “hinge” during filament and turns inside up. (G) Extruded polar tube and ejected sporoplasm (arrowhead) (). (H) Details of the anterior pole of the spore, the polar sac, and the penetrated anchoring disk are visible ( (I) polar filament of the manubrium type (). (A to D and F) TEM; (E) phase contrast; (G and H) SEM; (I) fresh, unstained. Scale bars: A and F, 0.5 μm; B, 25 nm; C and D, 100 nm; E, G, and 1,5 μm; H, 0.5 μm. Reprinted with permission from D. Vinckier and . (A), .(B to D), . (F), and B. S.Toguebaye and . (G and H). Abbreviations: AD, anchoring disk; d, diplokaryon; f, polar filament; g, Golgi apparatus; Nu, nucleus; Pa, anterior polaroplast; Ps, polar sac.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 9
FIGURE 9

The spore wall. (A) Uniform exospore (free spore) (); (B) spore wall of type (octospore) (); (C) layered exospore (); (D and E) exospore with tubular projections (); (F to H) exospore with filamentous projections, invisible in stained smears (G) (). (A to C, E, and H) TEM; (D) SEM; (F) interference phase contrast; (G) Giemsa stain. Scale bars: A to C, 100 nm;D, 1 μm; E, 0.5 μm; F to H, 10 μm. Reprinted with permission from M. Rausch (D) and (F to H). Abbreviations: E, endospore; EX, exospore; Pm, plasma membrane.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 10
FIGURE 10

Freeze-fracture of microsporidian spores. (A) Tangentially fractured spore wall of , showing the ectoplasmic face of the plasma membrane, the endospore with fibers, and the exospore with coarse fibers and granules. (B) Fracture through the sporophorous vesicle membrane of (arrowheads), showing irregular granular structure demonstrating that it is not a cytomembrane. (C) Tangential fracture through immature spore of a sp., showing the ectoplasmic face of the plasma membrane covered with intramembranous particles (IP) and intramembranous particles on the ectoplasmic face of the unit membrane enveloping the polar filament (asterisk). (D) Fractured spore of , showing cross-fractured polar filament coils (arrowhead) and the protoplasmic and ectoplasmic faces of the unit membrane ensheathing the polar filament. In mature spores the hemimembranes of the filament are nearly devoid of intramembranous particles. (E) Cross fractured polar filament. Note its solidlike appearance with an outer ring and a central spot of fine particles. (F) Fractured diplokaryon of . One nucleus (Nl) is cross-fractured.The second nucleus (N2) shows pores in the nuclear membrane. Arrow indicates the apposed nuclear membranes. Scale bars: A to F, 100 nm. Abbreviations: EN, endospore; Ex, exospore; N, nucleus, SW, spore wall; EF and PF, respective ectoplasmic and protoplasmic faces of a split unit membrane. Panels A and B are reprinted with permission from .

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 11
FIGURE 11

Gross morphology of the polar filament and anchoring apparatus. (A) Anisofilar filament ( sp.); (B) ejected anisofilar filament (polar tube) ); (C to E) spores with straight (manubroid) filament, visible in living spores (C) (), ejected (D) (arrowhead indicates the straight, wide part) (), and longitudinally sectioned (E) (arrowhead indicates the wide part and arrow indicates the narrow posterior part) (); (F) common type of filament anchoring, with a wide polar sac, layered anchoring disk, and all layers of the filament (except for the unit membrane cover) united with the anchoring disk (); (G and H) caplike polar sac, no visible anchoring disk, and collar-to-socket attachment of the filament (arrowheads) (G) () and (H) (); (I) presence of carbohydrates with α-glycol groups revealed byThiery's reaction (arrowheads) (). (A, and E to H) TEM; (B) Giemsa stain; (C) phase contrast; (D) hematoxylin stain; (I) PAS technique, TEM. Scale bars: A, F, and G, 100 nm; B, C, and D, 10 μm; H and I, 50 nm; E, 0.5 μm. Reprinted with permission from . (C, F, and I), . (G), and . (H). Abbreviations: AD, anchoring disk; f, polar filament; Pa, anterior part of polaroplast; Ps, polar sac.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 12
FIGURE 12

(A and B) Schematic representation of polar filament-polar sac connection in microsporidia. Typical microsporidia (A) and -like microsporidia (B) are shown. (C to E) Schematic representation of polar filament evagination (tip of the extrusion apparatus in a dormant spore [C]; polar sac-polar filament relationship in extruded spore [D]). Note that the structure labeled c serves as a hinge for the evaginating filament. (E) Cross section of the filament in a dormant spore. (F) Filament in an activated spore. (G) Cross section of the extruded filament. Modified with the permission of J. Lom and . Abbreviations: A, anchoring disk; a, polar filament wall; b, polar filament lumen; c, hinges; M, membrane ensheathing the polar filament; PS, polar sac; 1,2, and 3, layers seen in the filament.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 13
FIGURE 13

Fine structure of the polar filament. (A to C) Transversely sectioned filaments; 1 to 6 indicate the most easily observed layers in (A), (B), and (C). (D) Layering of the filament, showing the double layers of the outer (arrow) and inner (arrowhead) filament walls (). (E) Layering seen in immature spores. Note the difference in polar filament layers in the anterior and posterior coils (). (F and G) Fibrillar substructure of the polar filament. A filament after tryptic digestion (F) and the fibrillar substructure of one of the filament layers revealed by Thiery' s reaction for carbohydrates in sp. from (G) are shown. (H) Cross section of a filament stained byThiery's method (). TEM was used for all panels. Scale bars: A to C, F, and H, 50 nm; D, 25 nm; E,100nm, G, 0.5 μm. Reprinted with permission from . (A), . (B), . (C), G. Schubert (D), B. S.Toguebaye (E), Plenum Press (F and H), and E. Porchet-Hennere (E and G).

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 14
FIGURE 14

Freeze-fracture of microsporidian spores. (A) Tangential fracture of young spore of , showing the hypertrophied reticulum of the Golgi zone and cross and tangential fractures of several coils of the polar filament. Both faces (EF and PF) of the cytoplasmic membrane around the filament are shown. (B) Sporoblast of , showing the origin of the polar filament by coalescence of Golgi reticulum vesicles (arrow). (C) Longitudinal fracture through young spore, demonstrating that the polar filament is a solid cylinder enveloped by a cytoplasmic membrane with EF and PF faces; the EF face bears more numerous intramembranous particles; posterior vacuole membrane PF face is at arrow. (D) The polaroplast (arrow) in is revealed as a stack of membranes bearing intramembranous particles on both its hemimembrane faces. The ectoplasmic face (EF) of the spore plasma membrane (Pm) bears numerous intramembranous particles. Scale bars: A, C, and D, 0.5 μm; B, 250 nm. Reprinted with permission from . (A to C) and D. Vinckier (D). Abbreviations: g, Golgi zone; F, polar filament; EF and PF, respective ectoplasmic and protoplasmic faces of a split unit membrane; Pm, plasma membrane (ectoplasmic face).

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 15
FIGURE 15

Unusual types of filaments. (A) Posterior part of a short, straight filament of normal cytology (); (B) straight filament of Metchnikovellidae, ending with a “gland” (arrowhead) ( sp.); (C) short and completely coiled filament of covered by a honeycomblike surface layer (arrowhead); (D) transversely sectioned filament of (arrow indicates tubular material and arrowhead indicates the covering unit membrane); (E) transversely sectioned filament of (arrows indicate unit membrane folds); (F) filament of with the bulbous gland (arrowhead); (G and H) longitudinal (G) and transversal (H) sections of the filament covered with honeycomb layer (). TEM was used for all panels. Scale bars: A, D, and E, 50 nm; C and F, 0.5 μm; B, G, and H, 100 nm. Reprinted with permission from (A), . (C), . (D), J. Schrével (F), and H. G. Sheffield and C. S. Richards (G and H). Abbreviations: Nu, nucleus; Ps, polar sac, g, Golgi.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 16
FIGURE 16

Fine structure of the polaroplast. (A) The most common type of bilaminar polaroplast, with more closely packed anterior lamellae (); (B) polaroplast with three regions (wide lamellae, narrow lamellae, and tubules) ();(C and D) bilamellar polaroplast with exceptionally closely packed anterior lamellae (“cavum”) (); (E to G) three aspects of the transversly sectioned polaroplast, concentric lamellae (E) (), petallike arrangement (F) (), and tubules (G) (). TEM was used for all panels. Scale bars:A, B, D, F, and G, 100 nm;E,50 nm; C, 0.5 μm. Reprinted with permission from (A to E), . (B), and . (F and G). Abbreviations: Pa, anterior polaroplast; Pp, posterior polaroplast; T, tubules, f, polar filament.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 17
FIGURE 17

Gross morphology of the sporophorous vesicle. (A and B) The meronto-genetic sporophorous vesicle of , complete and sectioned; (C to E) three aspects of the octosporous sporophorous vesicle of ; (F) tetrasporous sporophorous vesicles of with two vesicles exhibiting macrospores (large arrows) and a reduced number of spores; (G to J) four aspects of the disporous vesicle of . (A to C and G) SEM; (D and H) phase contrast; (E and F) hematoxylin stain; (I) Giemsa stain; (J) TEM. Scale bars: A to C, 1 μm; D, E, F, and H, 5 μm;J, 0.5 μm; G and I,1 μm. Reprinted with permission from . (C and D),. (F), and . (J). Abbreviation: SE, sporophorous vesicle envelope.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 18
FIGURE 18

Ultrastructure of the sporophorous vesicle. (A and B) Initiation over wide areas of the sporont surface (arrowheads indicate envelope) (); (C) blisterlike initiation (arrowheads) (); (D) mature spores enclosed in individual sporophorous vesicles (); (E) blisterlike protuberances (arrowheads) of the individual vesicles stain darkly on the rosettelike dividing sporont (); (F and G) layered (arrowheads) merontogenetic sporophorous vesicle of showing surrounding mature spores (F) and initiation (G); (H and I) unusual types of thick sporophorous vesicles from (H) and (I) in which the envelope is identical to the exospore; (J and K) connected sporophorous vesicles (). (A to D, F to I, and K) TEM; (E and J) hematoxylin stain. Scale bars: A, 100nm;B,C, F,H,and I,50nm;D, 1 μm;E, 10 μn; G and K, 0.5 μm;J, 5 μm. Reprinted with permission from (A to C), (D and G), . (E),and . (J to K).Abbreviations:E, endospore; Ex, exospore; Mp, merogonial plasmodium; SE, sporophorous vesicle envelope.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 19
FIGURE 19

Exospore projections and inclusions of the episporontal space. (A and B) Fibrous material (arrowheads) connecting the exospore with the envelope (); (C) wide tubules from exospore to envelope (); (D) labyrinthlike tubular material (arrowheads) (); (E) tubular exospore-derived material (); (F) septate, exospore-derived tubules (); (G) uniform amorphous crystallike material (arrowheads) ( sp.); (H and I) two-layered crystals (arrowheads) (). (A to H) TEM; (I) hematoxylin stain. Scale bars: A, C to E, and H, 100 nm; B and F, 50 nm; G, 0.5 um; 1,5 μm. Reprinted with permission from . (A and B), . (E), . (F), and (H). Abbreviations: Ex, exospore; SE, sporophorous vesicle envelope; Sp, sporont.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 20
FIGURE 20

Exospore-derived envelopes and sporont-derived sacs. (A to C) Two steps in the initiation of an exospore-derived envelope. Arrowheads indicate the surface layer that forms the envelope and an envelope surrounding a mature spore (). (D) External part of a sporont which is transferred into an envelope (arrowheads) (). (E to G) Thick-walled cystlike sacs of , showing mature envelope (E), live cysts enclosing spores and free spores as indicated by arrowheads (F), and mature cysts (G). (H) Live fusiform sacs of an sp. (arrows indicate threadlike projections, and arrowheads indicate spores in the sacs and free in the cytoplasm. (A to E) TEM; (F and H) phase contrast; (G) SEM. Scale bars: A, B, and E, 50 nm; C and G, 1 μn; D, 0.5 μm; F and H, 5 μm Reprinted with permission from . (C) and . (E to G). Abbreviations: Ex, exospore; Pm, plasma membrane.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 21
FIGURE 21

Microsporidian-induced effects on the host cytology. (A) Gut epithelium cells filled with microsporidian spores (B) epithelium cells released into the gut lumen which can be mistaken for multisporous sporophorous vesicles (C) parasitophorous vacuole (D) host cell mitochondria (arrowheads) accumulated at the surface of a sporont (E) host nucleus (arrowheads) enveloping spores of (F) the xenoma with multilayered wall (arrowheads) and with the most immature stages of the microsporidian at the periphery (arrows indicate host nuclei) (A) SEM; (B) interference phase contrast; (C to F) TEM. Scale bars: A, 5 urn; B, 25 um; C, 50 nm; D, 0.5 urn; E and F, 1 um. Panel C is reprinted with permission from Abbreviations: MP, merogonial plasmodium; PM, plasma membrane; S, spore; SN, sporont; Sp, sporogonial plasmodium.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 22
FIGURE 22

(A) Groups of spores originating from an individual plasmodium (Giemsa stain). (B) Spores of a sporogonial plasmodium in intestinal biopsy (fluorescence, Calcofluor staining). (C) Uninucleate, initial stage. (D) Multinucleate plasmodium with elongate nuclei, some of which are dividing (arrows). Expanded perinuclear cisternae contain dense material (asterisks). First primordia of the extrusion apparatus (possible polar sac) appear as dense rings (arrowheads). (E) Dividing nucleus as in (D). Spindle plaques (arrowheads) and the spindle are situated across the shorter axis of the nucleus. (F) Association of a multinucleate plasmodium with the nucleus of the host enterocyte. (G) Infected enterocyte with spores is released into the intestine lumen. Scale bars: A and B, 5 urn; C, 0.5 um; D, 1 am; E, 250 nm; F and G, 2 um. (C to G) TEM. Reprinted with permission from M. A. Spycher (D and E) and J. M. Orenstein (F and G). Abbreviations: HN, host cell nucleus; S, spore.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 23
FIGURE 23

Formation of extrusion apparatus elements in multinucleate plasmodia of Polar sac (?) primordia are shown by arrows, and polar filament primordia are shown by arrowheads. (A) Initial stage. (B) Advanced sporogonial plasmodium. (C) Detail at high magnification. (D) More advanced plasmodium. A vacuole representing the primordium of the polaroplast and of the future posterior vacuole is associated with each nucleus (asterisk). (E) Both the polar sac and the vac-uole (asterisk) are associated with the nucleus. Vesicular outgrowth of the polar filament probably represents formation of the polaroplast (arrowheads). (F) Detail of the polar sac. TEM was used for all panels. Scale bars: A, B, and D, 1 um; C and E, 250 nm; F, 100 nm. Reprinted with permission from J. M. Orenstein (A and D), M. A. Spycher (B and C), and and I. Desportes-Livage (E and F).Abbreviations: Nu, nucleus; Ps, polar sac.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 24
FIGURE 24

Spore formation in (A) Origin of the sporo-blasts. In the sporoblast the former vacuole is split into an anterior vacuolar space, in which a lamellar polaroplast is formed (arrows) and a posterior part, the future posterior vacuole (asterisk). Polar filament coils start to be organized in the final form. (B) Detailed view of the polar sac, polar filament, lamellar polaroplast (large arrow), vesicular polaroplast (arrowhead), nucleus, and future posterior vacuole (asterisk). Note several dense vesicular structures above the polar sac and the opaque material between these vesicles and the polar sac (small arrows). (C) Nearly mature spore with a very thin exospore, relatively thick endospore, and characteristically coiled polar filament forming two rows. (D) Beginning of sporoblast formation.The anterior parts of the extrusion apparatus assemble near the plasmodium surface. Note that each polar sac is exteriorly lined with elongated vesicles (small arrows). TEM was used for all panels. Scale bars: A, 1 |xm; B to D, 250 nm. Reprinted with permission from J. M. Orenstein and (C and D). Abbreviations: Nu, nucleus; HN, host cell nucleus; Ps, polar sac.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 25
FIGURE 25

(syn. (Golgi is shown at arrowhead). (A) Initial meront surrounded by snugly adhering membrane of the future parasitophorous vacuole. (B) Detailed view of the membranous complex of the meront in panel A. (C and D) A large parasitophorous vacuole originates by progressive confluence of individual vacuoles around dividing parasites. A meront (arrow) is fully embedded in the host cell cytoplasm. (E) Fully formed vacuole with septa forming incomplete chambers around individual spores. TEM was used for all panels. Scale bars: A, C, and D, 1.0 um; B, 250 nm, E, 2 um. Reprinted with permission from M. A. Spycher (A to D) and J. M. Orenstein (E). Abbreviations: c, host cell cytoplasm; MR, meronts; Nu, nucleus; SB, sporoblasts; S, spore.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 26
FIGURE 26

(A) Spores on a smear (Giemsa stain); (B) SEM view of a broken parasitophorous vacuole with spores; (C) parasitophorous vacuole with meronts lining the vacuole borders (arrowheads) and sporogonial stages and spores in center of vacuole; (D) chains of sporoblasts inside the parasitophorous vacuole (arrows) (Giemsa stain); (E) early parasitophorous vacuole originating around three meronts (phase contrast); (F) fully formed parasitophorous vacuole with meronts adhering to vacuole border, sporonts, and sporoblasts detached to the vacuole interior; (G) young spore with organelles; arrow indicates polar filament early form; arrowhead indicates polar sac. (A) Mouse peritoneal exudate; (B and E to G) liver of SCID mouse; (C and D) rabbit chorioid plexus cell tissue culture. (E to G) TEM. Scale bars: A to D, 5 um; E to G, 0.5 um. Reprinted with permission from B. Koudela (B and E) and (C and D). Abbreviations: g, Golgi reticulum; Mr, meront; Nu, nucleus; Sb, sporoblast; Sn, sporont; Pv, posterior vacuole (collapsed).

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 27
FIGURE 27

spp. (A) Border of a parasitophorous vacuole.The canopy of blebs protruding into the vacuole is shown at arrow. (B to D) (B and C)Young spores with five filament coils; (D) extruded spore. (E to G) (E) Fully formed parasitophorous vacuole; (F) earlier vacuole with meronts, sporont, and sporo-blasts transforming into spores; (G) spore with organelles. A polar filament with a substructure of concentric rings is shown at the arrowhead. The three layers of the spore wall, the plasma membrane, and the endo- and exospore are indicated by the arrow. TEM was used for all panels. Scale bars: A to D, 0.5 urn; E, 2 urn; F, 1 um; G, 100 nm. Reprinted with permission from J. M. Orenstein (B to D) and A. Curry (E to G). Abbreviations: HM, host cell mitochondrion; MR, meront; Nu, nucleus; P, polaroplast lamellae; r, area with polyri-bosomes; SB, sporoblast; SN, sporont; Pv, posterior vacuole (distorted).

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 28
FIGURE 28

spp. (A) Binucleate meront in skeletal muscle cell, showing the plas-malemma covered by dense material forming connections between meronts (arrow) and protuberances into the host cell cytoplasm (arrowheads); (B) sporo-phorous vesicle with four presporoblast cells; (C) sporophorous vesicles with type I spores; (D) thick-walled type I spore with seven thick and two thin coils; (E and F) thin-walled type II spores with four isofilar coils. (A and B) TEM of in SCID mouse skeletal muscle (A) and RK-13 cell tissue culture (B); (C to F) in human brain (SEM [C] and TEM [D to F]). Scale bars: A, 0.5 urn;B and C, 1 urn; D to F, 100 nm. Panel B is reprinted with permission from E. U. Canning.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 29
FIGURE 29

spp. (A) Free spores (fresh); (B) fresh spores in sporophorous vesicles; (C) extruded spore; the polar tube extrudes subapically (arrowheads); (D) stained spores (Goodpasture's carbolfuchsin stain); (E) type I spores in sporophorous vesicles (semithin plastic section, methylene blue-azure II-basic fuchsin staining); (F) aggregate of type II spores in histology section (hematoxylin and eosin stain); (G) type I spores in a multisporous sporophorous vesicle; (H) type II spores in bi-sporous sporophorous vesicles; (I) extruded type II spore; (J) detail of tip of extruded type II spore, showing the tubular aspect of the polar tube. (A to C) , skeletal muscle homogenate of SCID mice. (D toj) , human brain (D to H) and human heart muscle (I andj). (A to C) Interference phase contrast; (G toJ)TEM. Scale bars: A to F, 5 p.m; G and H, 1 urn; I, 0.5 um;J, 100 nm. Reprinted with permission from B. Koudela (B and C) and J. M. Orenstein (J).

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 30
FIGURE 30

(A) Fresh spores (phase contrast); (B) meront; (C) meront enclosed by an inner membranous complex (arrow) of two adhering membranes (the inner, one supposedly belonging to the parasite and the outer one belonging to the host) and one outer host membrane (arrowhead); (D) cell boundary of the sporont, showing electron-dense material deposited on the innermost (parasite) membrane (arrowhead); (E) low-magnification view of infected mouse liver; (F) dividing diplokary-otic sporont; (G) mature spore enclosed in several membranous layers; (H) polar filament coils with substructure. (B to H) TEM. Scale bars: A, 5 urn; B and C, F, and G, 0.5 um; D and H, 100 nm; E, 1 (am. Reprinted with permission from J. A. Shadduck (D and F to H). Abbreviations: Mr, meront; Nu, nucleus; Sb, sporoblast; S, spore.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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Image of FIGURE 31
FIGURE 31

from human skeletal muscle. (A) Developmental stages (meronts?), showing the diplokaryotic nuclei; (B and C) details of the electron-dense material deposits in the form of membrane-bound tubules (B) or dense tubular strands (C) at the plasma membrane (arrowhead); (D) parasite cell showing large expansion of the vesiculotubular electron-dense material at the cell surface (arrowhead); (E) spore with PF arranged in a double coil; (F) construction of the meront surface of parasite of mosquito larvae is to a certain degree similar to the meront surface of TEM was used for all panels. Scale bars: A, 1 urn; B, C, and F, 100 nm; D, 250 nm; E, 0.5 um. Reprinted with permission from A. Cali and (A to E). Abbreviations: SB, sporoblast; S, spore.

Citation: Vávra J, Larsson J. 1999. Structure of the Microsporidia, p 7-84. In Wittner M, Weiss L (ed), The Microsporidia and Microsporidiosis. ASM Press, Washington, DC. doi: 10.1128/9781555818227.ch2
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