地表に現れたマントル由来の岩石に湧く泉で、どのような生物がいるか調べたところ、２７種の微生物の遺伝子が見つかった。周辺は強アルカリ性で、約４０億年前の地球に似た過酷な環境という。 そのうち、岩石に付着した細菌では、酸素を使った呼吸など生命維持に必要とされるエネルギーを得るための遺伝子を一つも持っていなかった。(どうやって生きてるのか…「常識外れ」の細菌、泉で発見 朝日新聞 DIGITAL7/21(金) 23:27）
The ISME Journal , (21 July 2017) | doi:10.1038/ismej.2017.111
Shino Suzuki, Shun’ichi Ishii, Tatsuhiko Hoshino, Amanda Rietze, Aaron Tenney, Penny L Morrill, Fumio Inagaki, J Gijs Kuenen and Kenneth H Nealson
Water from The Cedars springs that discharge from serpentinized ultramafic rocks feature highly basic (pH=~12), highly reducing (Eh<−550 mV) conditions with low ionic concentrations. These conditions make the springs exceptionally challenging for life. Here, we report the metagenomic data and recovered draft genomes from two different springs, GPS1 and BS5. GPS1, which was fed solely by a deep groundwater source within the serpentinizing system, was dominated by several bacterial taxa from the phyla OD1 (‘Parcubacteria’) and Chloroflexi. Members of the GPS1 community had, for the most part, the smallest genomes reported for their respective taxa, and encoded only archaeal (A-type) ATP synthases or no ATP synthases at all. Furthermore, none of the members encoded respiration-related genes and some of the members also did not encode key biosynthesis-related genes. In contrast, BS5, fed by shallow water, appears to have a community driven by hydrogen metabolism and was dominated by a diverse group of Proteobacteria similar to those seen in many terrestrial serpentinization sites. Our findings indicated that the harsh ultrabasic geological setting supported unexpectedly diverse microbial metabolic strategies and that the deep-water-fed springs supported a community that was remarkable in its unusual metagenomic and genomic constitution.
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