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Bacteria That Grow at 250°C Firmation

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Bacteria That Grow at 250°C Firmation _NA_ru_~__ V_O_L._~_2_RmE ___ I_~_3 ______________________ NEWSANDVIEWSI __________________________________ ~~=I Thus, while data from mutations that af­ crystallin and similar polymorph isms in as at 20°C. Just a few more should provide fect splicing confirm the idea that the se­ other proteins could have arisen from aber­ the same stability at 250°C. It seems quite quences of splice sites are crucial to their rant splices like those discussed here. possible therefore that these newly dis­ ability to function, they also raise impor­ Gallwitz and his colleagues have shown covered extreme thermophiles may have tant questions about the complex mech­ both that mutations in the 5' splice site of proteins not fundamentally different from anism that governs whether or not a par­ the yeast actin gene do not give rise to cryp­ the norm, though Baross and Deming do ticular splice site will be used and with tic splices l7 and that yeast is unable to report that while all the usual protein which partner it will be coupled. Such com­ remove vertebrate introns from hybrid amino acids are present, there are in addi­ plexity reflects the extreme versatility of genes22 . The adaptability of the splicing tion five of unknown identity. messenger RNA splicing in higher eukar­ machinery demonstrated by the thalas­ The new bacteria, like other extreme yotes, which in turn may contribute to the saemia mutations may therefore be restric­ thermophiles, are probably archae­ evolution of new proteins21 . The use of a ted to higher eukaryotes, and genetic bacteria, organisms which, with a long cryptic splice site allows the testing of a new defects such as these may be a price we pay separate evolution from the more cosmo­ protein, often without altogether giving up for the evolutionary advantages we enjoy. 0 politan eubacteria, have membranes based the old oneI,7.18. on a different design - long-chain ether Stephen Mount and Joan Steitz are at the 56 In the thalassaemias none of the new ar­ Department of Molecular Biophysics and lipids . that span from one surface to the rangements is at all satisfactory, but it is Biochemistry, Yale University, 333 Cedar other. They form thermostable structures. easy to see how the optional exon in aA- Street, New Haven, Connecticut 06510. Can the DNA of these bacteria be kept in its double helix? Unless it can, it would be Microbiology difficult to synchronize replication of the complementary strands and impossible to repair them. Perhaps there are special pro­ teins that maintain the duplex con­ Bacteria that grow at 250°C firmation. It is easy to speculate on how the from A.E. Walsby building blocks of life can be made thermo­ stable, of course; the great achievement of THE title of Ray Bradbury's science fiction growth at 250°C was very clear cut: the Baross and colleagues has been to recog­ novel Fahrenheit 451 is a reference to the number of bacteria increased a hundred­ nize that bacteria were growing at such temperature at which paper ignites. Almost fold over a few hours, as did the protein exceptional temperatures when the stranger than fiction is the report in this they contained. There are indications that conventional wisdom must have been issue of Nature by J .A. Baross and J. W. the bacteria will grow with similar vigour at shouting that it was impossible. Demingl that there are forms of life 300°C though this has yet to be confirmed. Their finding also has several important capable of growing at even higher temper­ And even this may not be the upper limit. implications. The bacteria must produce atures, 250°C (482°F) or more. This as­ If only 250°C should transpire to be the highly thermostable enzymes and some tounding discovery not only challenges our maximum for growth this sets a new record may have application in laundry or other preconceptions about the limits at which by a large margin: until now the highest industrial processes involving high organic life can survive, it also alerts us to temperature for a thermophile, also from a temperatures. They might also provide the the possibility that life may exist within hot submarine floor, was 105°C (ref.3). basis of a new natural gas industry, as regions of the Earth's crust (and perhaps The latest discovery amply confirms Baross and Deming have shown that these on other planets) previously presumed Brock's postulate that "certain kinds of organisms generate hydrogen, carbon sterile on account of their elevated tem­ bacteria may perhaps be able to live in any monoxide and especially methane during peratures. Perhaps life may even have boiling habitat that contains liquid water" growth. For pure science, though, there is originated in those superheated systems. and his observation that "the upper tem­ also substance for speculation on the origin The paper by Baross and Deming is a se­ perature for life has not yet been of life. While I do not concur with the idea 7 quel to that by Baross, Lilley and Gordon2 defined"4. that a single, extremely unlikely, chance which describes complex communities of I must admit that my first reaction on event was required to set life in motion, it is bacteria in hot water rising from sulphide­ reading the manuscript of Baross and Dem­ clear that the time required for evolution of encrusted vents located along tectonic rifts ing, arriving as it did on the eve of April chemical conglomerations into living and ridges on the deep ocean floor. Some Fool's Day, was one of incredulity. Are we forms would be much less at 250°C than at of these communities occurred at not, after all, conditioned to believe that the ambient temperature. Moreover, life temperatures exceeding 360°C and from most germs will succumb after Pasteur­ could have originated much earlier in the them were isolated bacteria that could ization at a mere 70°C, and that just 20 min­ development of the cooling Earth than has grow in the laboratory at 100°C, obligate utes at 120°C in the autoclave will exter­ been previously considered. And what lies thermophiles whose growth ceased below minate the most resistant bacterial spore? below those submarine cisterns spewing 75°C. Baross et al. speculated that these Have we not also learned in biochemistry forth their bacterial brew - other forms of bacterial communities might be the source classes that at these scalding temperatures life, perhaps? My experience with another of much methane, hydrogen and carbon proteins denature, lipids run to ghee and bizarre life form, the square bacterium8, is monoxide that vents into the ocean. duplex DNA melts into separate strands? that once you have discovered the first one Baross and Deming have now grown Some of the same questions have been others are not then so difficult to find. 0 some of these bacteria in enriched seawater asked before, of course, in relation to enclosed in a titanium syringe surrounded thermophilic bacteria growing at up to by a chamber heated to 250°C and 100°C. But will the same explanations hold A.E. Walsby is Melville Wills Professor of Botany at the University of Bristol, Woodland pressurized at 265 atmospheres, the hydro­ at 250°C? To take the case of proteins, for Road, Bristol BS8 I UO. static pressure at the depth (2,500 m) of the example, it is known that they are not all ocean floor where the bacteria were found. denatured like albumen in the five-minute I. Baross. J.A. & Deming. J.W. Nature3412. 423 (1983). At this pressure seawater does not boil until egg, and not all enzymes, even from meso­ 2. Baross. J.A. et 01.298.366 (1982). it reaches 460°C. Several different bacteria philes, are inactivated by boiling, the bio­ 3. Steller. K.O. Nature 300.258 (1982). grew in this pressure-cooker arrangement, chemist's routine control. It can be argued 4. Brock, T.D. Thermophil;c Microorganisms and Life aI Hi~h Temperatures (Springer. New York, 1978). doubling in number in about 40 minutes­ from the thermodynamics of protein 5. De Rosa, M. et 01. Phytochemistry IS. 143 (1975). the same sort of growth rate commonly en­ denaturation that only a few extra hydro­ 6. Langworthy, T.A. Biochim. biophys. Acta 389. 477 (1977). 7. Hoyle, F. & Wickramsinghe. C. Evolution from Space countered in many mesophilic bacteria at gen bonds or salt bridges are needed to pro­ (Dent. London, 1981). ambient temperatures. The evidence for vide the same stability in a protein at 100°C 8. Walsby, A.E. Nature 283,69 (1980). 0028·0836/83/220381-01$01.00 C 1983 Macmillan Journals LId .
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