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Chapter 14 : Deep-Sea Geomicrobiology
Category: Applied and Industrial Microbiology
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The rapid development and growth of geomicrobiology can partially be attributed to discoveries in the last several decades of unique extremophiles present in many different harsh environments that play key roles in the biogeochemistry that occurs in these environments. The development of new technologies and experimental approaches in geomicrobiology and in the studies of extremophiles has spawned a revolution that will surely have profound social and economic impact now and in the future. The chapter focuses on the piezophilic members of the extremophiles, with an emphasis on geomicrobiological considerations. The deep sea in general is an oligotrophic environment, except in areas of cold seeps and hydrothermal vents. The pressure-induced changes in fatty acid composition are comparable to those induced by temperature changes and that homeoviscous adaptation of membrane lipids occurs in piezophilic bacteria in response to pressure. The majority of the fatty acids were unsaturated, with one, five, or six double bonds. The biosynthesis of monounsaturated fatty acids was significantly inhibited (10 to 37%) by the addition of cerulenin, whereas the concentrations of polyunsaturated fatty acid (PUFA) increased two to four times. Lipids and stable carbon isotopes preserved in lipids have proven to be excellent biosignatures applied to deep-sea geomicrobiology. Fatty acid compositions of piezophilic bacteria are discussed in this chapter.
Chemical structures of PUFA.
Three-dimensional views showing the temperature (T)-pressure (P) dependence of the exponential growth rate constant (k) of strain SC1 (A) and Moritella strain PE36 (B) from the North Pacific Ocean. The PTk diagram allows a reasonable, unambiguous determination of k max, T k max , and P k max of piezophilic bacterial growth (adapted from reference 125 ).
Total microbial utilization (incorporation plus respiration) of [14C]glutamic acid at 3°C and in situ (44 MPa) pressure (filled circles) or atmospheric pressure (open circles) in sediment suspensions prepared from depths of 1, 5, and 15 cm in boxcores from stations A (depth, 4,470 m) and B (depth, 4,850 m). Respiration accounted for 89 to 94% of total substrate utilization at both pressures (adapted from reference 28 ).
Total microbial utilization (incorporation plus respiration) of [14C]glutamic acid at 3°C and in situ (44 MPa) pressure (filled circles) or atmospheric pressure (open circles) in seawater suspensions of particulates from temperature-compromised sediment trap sample A-7 (depth, 4,463 m) and cold trap sample B-20 (depth, 4,830 m). Respiration accounted for 84 to 89% of total substrate utilization at both pressures (adapted from reference 28 ).
Bacterial fraction of “total” benthic biomass (excluding protozoa) as a function of depth in the ocean (adapted from reference 95 ).
G° plotted versus pressure and constant temperature (2°C) for O2 (a), NO3 (b), Fe2O3 (s) (c), and CO2 (d) reduction reactions.
Sequence of microbially mediated reduction reactions based on values of electron activity at biological standard state (p8 o w) at 25°C and 1 bar (105 Pa) (a) and 2°C and 400 bar (4 × 107 Pa) (b). The p8 o w values are calculated per Johnson et al. ( 51 ) and Amend and Teske ( 6 ). TEAP, terminal electron-accepting process.
Representative fatty acids of the five piezophilic genera Moritella, Colwellia, Photobacterium, Shewanella, and Psychromonas. Evolutionary distance tree of the domain Bacteria was taken from reference 49 .
Summary of possible biosynthetic pathways of fatty acyl chains in piezophilic bacterial membrane lipids (modified from references 97 and 118 with permission of the publishers). The saturated and monounsaturated fatty acids are synthesized by the FAS pathway common to members of the domain Bacteria, which include the aerobic (type I) and anaerobic (type II) branches. The PUFA found in piezophilic bacteria are probably synthesized via the PKS pathway, which appears to be unique to marine bacteria. Biosynthesis of PUFA by an aerobic mechanism through sequential elongation and desaturation reactions appears less likely to occur in piezophilic bacteria. Ac-ACP, acetyl-acyl carrier protein; Mal-ACP, malonyl-acyl carrier protein; DH, dehydrase; ER, enoyl reductase; KR, 3-ketoacyl reductase; KS, 3-ketoacylsynthase.
The calculated carbon isotopic fractionation, ε (ε = αs/p -1) × 1,000, of whole cell biomass and selected fatty acids biosynthesized by Moritella japonica DSK1 at 0.1, 10, 20, and 50 MPa, where c is defined as αs/p = (1,000 + δs)/(1,000 + δp), δs is the carbon isotopic ratio of substrate (glucose), and δp is that of product (cell biomass and fatty acids).
Piezophilic microorganisms isolated from various sources a
Fatty acid compositions of piezophilic bacteria a
Stable carbon isotopic composition of fatty acids in M. japonica DSK1 grown on glucose at various pressures a