Prokaryotic extremophiles were the first representatives of life on Earth and they are responsible for the genesis of geological structures during the evolution and creation of all currently known ecosystems. Flexibility of the genome probably allowed life to adapt to a wide spectrum of extreme environments. As a result, modern prokaryotic diversity formed in a framework of physico-chemical factors, and it is composed of: thermophilic, psychrophilic, acidophilic, alkaliphilic, halophilic, barophilic, and radioresistant species. This artificial systematics cannot reflect the multiple actions of different environmental factors since one organism could unite characteristics of several extreme-groups. In this review we show the current status of studies in all fields of extremophiles and summarize the limits of life for different species of microbial extremophiles. We also discuss the finding of extremophiles from unusual places such as soils, and briefly review recent studies of microfossils in meteorites in the context of the significance of microbial extremophiles to Astrobiology.
A novel alkaliphilic, sulfate-reducing bacterium, strain MLF1 T , was isolated from sediments of soda Mono Lake, California. Gram-negative vibrio-shaped cells were observed, which were 0?6-0?761?2-2?7 mm in size, motile by a single polar flagellum and occurred singly, in pairs or as short spirilla. Growth was observed at 15-48 6C (optimum, 37 6C), >1-7 % NaCl, w/v (optimum, 3 %) and pH 8?0-10?0 (optimum, 9?5). The novel isolate is strictly alkaliphilic, requires a high concentration of carbonate in the growth medium and is obligately anaerobic and catalasenegative. As electron donors, strain MLF1 T uses hydrogen, formate and ethanol. Sulfate, sulfite and thiosulfate (but not sulfur or nitrate) can be used as electron acceptors. The novel isolate is a lithoheterotroph and a facultative lithoautotroph that is able to grow on hydrogen without an organic source of carbon. Strain MLF1 T is resistant to kanamycin and gentamicin, but sensitive to chloramphenicol and tetracycline. The DNA G+C content is 63?0 mol% (HPLC). DNA-DNA hybridization with the most closely related species, Desulfonatronum lacustre Z-7951 T , exhibited 51 % homology. Also, the genome size (1?6610 9 Da) and T m value of the genomic DNA (71±2 6C) for strain MLF1 T were significantly different from the genome size (2?1610 9 Da) and T m value (63±2 6C) for Desulfonatronum lacustre Z-7951 T . On the basis of physiological and molecular properties, the isolate was considered to be a novel species of the genus Desulfonatronum, for which the name Desulfonatronum thiodismutans sp. nov. is proposed (the type strain is MLF1 T
A novel, obligately anaerobic, mesophilic, haloalkaliphilic spirochaete, strain ASpG1 T , was isolated from sediments of the alkaline, hypersaline Mono Lake in California, USA. Cells of the Gramnegative strain were motile and spirochaete-shaped with sizes of 0?2-0?2268-18 mm. Growth of the strain was observed between 10 and 44˚C (optimum 37˚C), in 2-12 % (w/v) NaCl (optimum 3 % NaCl) and between pH 8 and 10?5 (optimum pH 9?5). The novel strain was strictly alkaliphilic, required high concentrations of carbonates in the medium and was capable of utilizing D-glucose, fructose, maltose, sucrose, starch and D-mannitol. End products of glucose fermentation were H 2 , acetate, ethanol and formate. Strain ASpG1 T was resistant to kanamycin and rifampicin, but sensitive to gentamicin, tetracycline and chloramphenicol. The G+C content of its DNA was 58?5 mol%. DNA-DNA hybridization analysis of strain ASpG1 T with its most closely related species, Spirochaeta alkalica Z-7491 T , revealed a hybridization value of only 48?7 %. On the basis of its physiological and molecular properties, strain ASpG1 T appears to represent a novel species of the genus Spirochaeta, for which the name Spirochaeta americana is proposed (type strain ASpG1 T =ATCC BAA-392 T =DSM 14872 T ).The genus Spirochaeta contains a group of free-living, saccharolytic, obligately or facultatively anaerobic, helixshaped bacteria (Canale-Parola, 1977, 1984. Analysis of 16S rRNA gene sequences has shown that the spirochaetes represent a monophyletic phylum within the Bacteria (Paster et al., 1991). At the time of writing, the genus Spirochaeta contained 13 species of bacteria. These organisms occur in a wide variety of freshwater and marine environments (Canale-Parola, 1992), such as aquatic habitats (Spirochaeta aurantia) (Breznak & Canale-Parola, 1975), freshwater mud (Spirochaeta zuelzerae, Spirochaeta stenostrepta) (Canale-Parola, 1980), marine mud (Spirochaeta isovalerica, Spirochaeta litoralis) (Hespell & Canale-Parola, 1970;Harwood & Canale-Parola, 1983), oilfields (Spirochaeta smaragdinae) (Magot et al., 1997) and microbial mats (Teal et al., 1996). Some members of the genus Spirochaeta are microbial extremophiles that inhabit environments with extremes of salinity, alkalinity, pressure and/or temperature. The spirochaete extremophiles may harbour important enzymes and proteins and, consequently, are of particular interest to biotechnologists (Bermudes et al., 1987;Barth et al., 1991;Munson et al., 1993).Prior studies have shown that some species of the genus Spirochaeta are naturally resistant to sulfide concentrations at levels that inhibit the growth of many other microorganisms. The mesophilic halophile Spirochaeta halophila was isolated from black mud (smelling strongly of H 2 S) of Solar Lake, a high-salinity pond on the Sinai shore of the Gulf of Aqaba (Greenberg & Canale-Parola, 1976). The obligate anaerobe strain GS-2 is a mesophilic barophile that was isolated from sulfide-rich mud samples collected at a depth of 2550 m near deep-sea hydrotherm...
A novel, psychrotolerant, facultative anaerobe, strain FTR1 T , was isolated from Pleistocene ice from the permafrost tunnel in Fox, Alaska. Gram-positive, motile, rod-shaped cells were observed with sizes 0?6-0?760?9-1?5 mm. Growth occurred within the pH range 6?5-9?5 with optimum growth at pH 7?3-7?5. The temperature range for growth of the novel isolate was 0-28 6C and optimum growth occurred at 24 6C. The novel isolate does not require NaCl; growth was observed between 0 and 5 % NaCl with optimum growth at 0?5 % (w/v). The novel isolate was a catalase-negative chemoorganoheterotroph that used as substrates sugars and some products of proteolysis. The metabolic end products were acetate, ethanol and CO 2 . Strain FTR1T was sensitive to ampicillin, tetracycline, chloramphenicol, rifampicin, kanamycin and gentamicin. 16S rRNA gene sequence analysis showed 99?8 % similarity between strain FTR1 T and Carnobacterium alterfunditum, but DNA-DNA hybridization between them demonstrated 39±1?5 % relatedness. On the basis of genotypic and phenotypic characteristics, it is proposed that strain FTR1 T (=ATCC BAA-754 T =JCM 12174 T =CIP 108033 T ) be assigned to the novel species Carnobacterium pleistocenium sp. nov.
96W). The cells of strain OGL-20PT have an irregular coccoid shape and are motile with a single flagellum. Growth was observed within a pH range of 5.0"8.5 (optimum pH 7.0), an NaCl concentration range of 1-5 % (w/v) (optimum 3 %) and a temperature range of 55-94 6C (optimum 83-85 6C). The novel isolate is strictly anaerobic and obligately dependent upon elemental sulfur as an electron acceptor, but it does not reduce sulfate, sulfite, thiosulfate, Fe(III) or nitrate. Proteolysis products (peptone, bacto-tryptone, Casamino acids and yeast extract) are utilized as substrates during sulfur reduction. Strain OGL-20P T is resistant to ampicillin, chloramphenicol, kanamycin and gentamicin, but sensitive to tetracycline and rifampicin. The G+C content of the DNA is 52.9 mol%. The 16S rRNA gene sequence analysis revealed that strain OGL-20P T is closely related to Thermococcus coalescens and related species, but no significant homology by DNA-DNA hybridization was observed between those species and the new isolate. On the basis of physiological and molecular properties of the new isolate, we conclude that strain OGL-20P T represents a new separate species within the genus Thermococcus, for which we propose the name Thermococcus thioreducens sp. nov. The type strain is OGL-20P
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