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Category: Bacterial Pathogenesis
Protein Targeting during Bacillus subtilis Sporulation, Page 1 of 2
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The first published reports of sporulation were by Ferdinand Cohn in Bacillus subtilis and Robert Koch in Bacillus anthracis in 1877 in the Zeitschrift für Plänzenbiologie ( 1 , 2 ). In addition to being among the earliest published reports of bacteria, these articles provided the initial demonstration that bacteria have an internal cellular organization. Cohn and Koch described intracellular membrane-bound compartments of different sizes and positions within the cell. Despite these striking original observations, bacteria were considered for much of the 20th century to be “bags of enzymes” that lacked any discernible spatial organization ( 3 ). However, in the past two decades, numerous examples, including dedicated intracellular compartments such as magnetosomes, the presence of a defined orientation of the chromosome, and the polarity of the chemotactic apparatus have emphatically demonstrated that bacterial cells exhibit an intracellular organization that, while less complex than eukaryotic cells, is nonetheless a critical and significant part of their physiology.
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Morphological and protein asymmetry during early stages in sporulation. A. Following entry into sporulation (i), cells establish an asymmetric septum (ii), dividing the sporangium into two unequally sized compartments, the forespore and the mother cell. During engulfment, the septum begins to curve (iii) and continues to curve (iv) until it is attached to the mother cell by only a small patch. Finally, the forespore pinches off from the mother cell (v) and forms a membrane-bounded compartment containing a thick layer of peptidoglycan (gray). Shown are fluorescent microscopy images using the membrane stain FM4-64 (left) and schematic cartoons (right). B. FtsZ rings (Z rings; black) are located at mid-cell during growth (left), but upon entry into sporulation (right), are seen initially in a bipolar pattern and eventually in a unipolar pattern before formation of the asymmetric septum. C. SpoIIE (gray) initially forms “E-rings” that are seen near the bipolar Z rings (left) but following formation of the polar septum (right), SpoIIE is seen on both the mother cell and forespore faces, with apparent enrichment on the forespore face.
Morphological and protein asymmetry during early stages in sporulation. A. Following entry into sporulation (i), cells establish an asymmetric septum (ii), dividing the sporangium into two unequally sized compartments, the forespore and the mother cell. During engulfment, the septum begins to curve (iii) and continues to curve (iv) until it is attached to the mother cell by only a small patch. Finally, the forespore pinches off from the mother cell (v) and forms a membrane-bounded compartment containing a thick layer of peptidoglycan (gray). Shown are fluorescent microscopy images using the membrane stain FM4-64 (left) and schematic cartoons (right). B. FtsZ rings (Z rings; black) are located at mid-cell during growth (left), but upon entry into sporulation (right), are seen initially in a bipolar pattern and eventually in a unipolar pattern before formation of the asymmetric septum. C. SpoIIE (gray) initially forms “E-rings” that are seen near the bipolar Z rings (left) but following formation of the polar septum (right), SpoIIE is seen on both the mother cell and forespore faces, with apparent enrichment on the forespore face.
Localization of septal proteins early in sporulation. A. The SpoIIIE DNA translocase (red) localizes to the asymmetric septum (i) because of the presence of DNA (blue) and mediates DNA pumping into the forespore (ii). Following completion of septation, SpoIIIE is found in the forespore membrane at the last point of contact with the mother cell (iii). B. The pro-σE processing enzyme SpoIIGA (yellow) initially localizes to the sites of incipient septum formation (i) and then to the mother cell face of the asymmetric septum (ii). The SpoIIR signaling protein (green) is made in the forespore and crosses the forespore membrane where it presumably interacts with and activates SpoIIGA, although it is also seen in the forespore following completion of septation. C. SpoIIB (aqua) initially colocalizes with FtsZ (orange) during the process of Z-ring constriction and remains in the polar septum following completion of septation. The SpoIIM (light blue), SpoIIP (dark blue), and SpoIID (purple) proteins proceed to localize to the now curved asymmetric septum.
Localization of septal proteins early in sporulation. A. The SpoIIIE DNA translocase (red) localizes to the asymmetric septum (i) because of the presence of DNA (blue) and mediates DNA pumping into the forespore (ii). Following completion of septation, SpoIIIE is found in the forespore membrane at the last point of contact with the mother cell (iii). B. The pro-σE processing enzyme SpoIIGA (yellow) initially localizes to the sites of incipient septum formation (i) and then to the mother cell face of the asymmetric septum (ii). The SpoIIR signaling protein (green) is made in the forespore and crosses the forespore membrane where it presumably interacts with and activates SpoIIGA, although it is also seen in the forespore following completion of septation. C. SpoIIB (aqua) initially colocalizes with FtsZ (orange) during the process of Z-ring constriction and remains in the polar septum following completion of septation. The SpoIIM (light blue), SpoIIP (dark blue), and SpoIID (purple) proteins proceed to localize to the now curved asymmetric septum.
Localization of septal proteins later in sporulation. A. Expression of SpoIIIAH (lime) is under control of σE and it is initially found in all of the mother cell membrane (i). Expression of SpoIIQ (purple) is under control of σF and it is initially found in the forespore septal membrane. Interaction of SpoIIQ and SpoIIIAH in the septal intermembrane space leads to localization of SpoIIIAH to the septum (ii), and this interaction continues until late in engulfment (iii). B. Initially, contact between SpoIIQ in the forespore membrane and SpoIIIAH in the mother cell membrane is prevented because of the presence of peptidoglycan. However, removal of this layer allows contact between the two proteins presumably through “extracellular” domains, resulting in the enrichment of SpoIIIAH at the septum. C. SpoIVFB (red) is initially observed in all mother cell membranes, but it eventually is “captured” by SpoIVFA (orange) and becomes enriched at the forespore in a complex with the SpoIVFB and BofA. D. SpoIVFA interacts with a number of proteins in the forespore outer membrane including SpoIID (green), SpoIIP (dark blue), SpoIIM (light blue), SpoIIIAH (lime), and SpoIIQ (purple).
Localization of septal proteins later in sporulation. A. Expression of SpoIIIAH (lime) is under control of σE and it is initially found in all of the mother cell membrane (i). Expression of SpoIIQ (purple) is under control of σF and it is initially found in the forespore septal membrane. Interaction of SpoIIQ and SpoIIIAH in the septal intermembrane space leads to localization of SpoIIIAH to the septum (ii), and this interaction continues until late in engulfment (iii). B. Initially, contact between SpoIIQ in the forespore membrane and SpoIIIAH in the mother cell membrane is prevented because of the presence of peptidoglycan. However, removal of this layer allows contact between the two proteins presumably through “extracellular” domains, resulting in the enrichment of SpoIIIAH at the septum. C. SpoIVFB (red) is initially observed in all mother cell membranes, but it eventually is “captured” by SpoIVFA (orange) and becomes enriched at the forespore in a complex with the SpoIVFB and BofA. D. SpoIVFA interacts with a number of proteins in the forespore outer membrane including SpoIID (green), SpoIIP (dark blue), SpoIIM (light blue), SpoIIIAH (lime), and SpoIIQ (purple).
Localization of proteins involved in spore coat and cortex assembly. A. SpoVM (green) has an intrinsic affinity for the forespore. B. SpoVD (red) and SpoVE (orange) form a complex at the outer forespore membrane. C. In the absence of SpoVE, SpoVD is found throughout the mother cell membrane.
Localization of proteins involved in spore coat and cortex assembly. A. SpoVM (green) has an intrinsic affinity for the forespore. B. SpoVD (red) and SpoVE (orange) form a complex at the outer forespore membrane. C. In the absence of SpoVE, SpoVD is found throughout the mother cell membrane.