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Chapter 16 : Physiology and Biochemistry of Methanocaldococcus jannaschii at Elevated Pressures
Category: Applied and Industrial Microbiology
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Methanocaldococcus jannaschii was originally isolated from the vicinity of a hydrothermal vent at a depth of 2,600 m, making it an ideal candidate for studies of pressure effects on the physiology of a deep-sea archaeon. This chapter summarizes the effects of pressure on selected proteins, lipids, and gene expression levels of M. jannaschii, one of the few known hyperthermophilic piezophiles, and presents a few prospects for future research. Methane has been used to measure growth rates of M. jannaschii at elevated pressures. Pressure effects on protein folding and reaction rates are based on Le Chatelier’s principle. Although it is difficult to generalize, some trends have emerged from recent studies of pressure effects on protein stability, at least below 200 MPa. Archaeal lipids consist primarily of isoprenoid hydrocarbons and alkylglycerol ether-derived polar lipids not found in bacteria or eukaryotes. The chapter has summarized how pressure affects the growth, membrane composition, and gene expression profiles of M. jannaschii, as well as pressure effects on the activity and stability of several of the organism’s key enzymes. These studies have thus expanded our understanding of how pressure affects the biochemistry and physiology of a hyperthermophilic piezophile. One strategy for addressing this question is to examine pressure effects on the activity of transcriptional regulators. For example, piezotolerant host strains might be generated with the aim of using pressure as an operational variable to regulate recombinant protein production.
Life in the temperature-pressure plane. Horizontal solid lines represent three isobars where life is known to exist: atmospheric pressure (line A), the isobar in the depths of the Red Sea (line B), and the isobar near the deep-sea hydrothermal vents from which M. jannaschii was isolated (line C). Vertical lines represent the isotherms of the cold deep sea (line D) and the Mediterranean Sea (E). Question marks represent uncertainty with regard to the upper temperature and pressure limits of life. Reproduced from reference 20 .
Distribution of hyperthermophilic archaea isolated from deep-sea hydrothermal vents (○), coastal marine hydrothermal vents and terrestrial hot springs (●), and an oil field reservoir (▲). M. jannaschii was isolated from the EPR at 21°N, indicated by “e” (○). Reprinted from reference 98 with permission of the publisher.
Schematic of the hyperbaric bioreactor with gas recycle designed by Miller, Shah, Nelson, and Clark. DP, digital pressure gauge; TC, electronic temperature controller; M, motor; OT, oxygen trap; GC, gas chromatograph; AGC, anaerobic glove chamber; PG, pressure generator; GB, gas booster; LC, liquid compressor; RP, recirculation pump; F, filter; SL, gas sample loop. Reproduced from the protocol by Nelson and Clark in reference 29.
Doubling times calculated from methane production rates as a function of pressure at 86°C (●) and 90°C (○). Based on data from reference 23 .
Schematic of the 1.15-liter high-pressure, high-temperature bioreactor system designed by Park and Clark. SSR, solid-state relay; TC, temperature controller; OT, oxygen trap; CA, compressed air; RG, regulator. Reproduced from reference 27 .
Scanning electron microscopy images of M. jannaschii after decompression for 5 min or 1 s. Cell rupture resulted in a negligible apparent turbidity increase when samples of M. jannaschii grown at 260 atm and 80°C were rapidly (<1 s) decompressed. However, after a 5-min decompression period, an increase in turbidity was evident. Adapted from reference 27 .
Structure of the archaeol (A), caldarchaeol (B), and the unique macrocyclic archaeol (macrocyclic diether) (C) lipids of M. jannaschii.
Effect of elevated pressure on thermal half-lives and activity of enzymes from M. jannaschii a
Distribution of core polar lipids in M. jannaschii for different growth pressures at 86°C a