Abstract：
The deep marine sediments represent a major repository of organic matter whilst hosting a great number of uncultivated microbes. Microbial metabolism plays a key role in the recycling of organic matter in the deep marine sediments. D-amino acids (DAAs) and DAA-containing muropeptides, an important group of organic matter in the deep marine sediments, are primarily derived from bacterial peptidoglycan decomposition. Archaea are abundant in the deep ocean microbiome, yet their role in DAA metabolism remains poorly studied. Here, we report bioinformatic investigation and enzymatic characterization of deep marine sedimentary archaea involved in DAA metabolism. Our analyses suggest that a variety of archaea, particularly the Candidatus Bathyarchaeota and the Candidatus Lokiarchaeaota, can metabolize DAAs. DAAs are converted into L-amino acids via amino acid racemases (Ala racemase, Asp racemase and broad substrate specificity amino acid racemase), and converted into α-keto acid via d-serine ammonia-lyase, whereas DAA-containing di-/tri-muropeptides can be hydrolyzed by peptidases (dipeptidase and D-aminopeptidase). Overall, this study reveals the identity and activity of deep marine sedimentary archaea involved in DAA metabolism, shedding light on the mineralization and biogeochemical cycling of DAAs in the deep marine sediments.
摘要：
深海沉积物是有机物的主要储存库，同时蕴藏着大量未培养的微生物。微生物代谢在深海沉积物中有机质的循环利用中起着关键作用。D-氨基酸（DAA）和含DAA的乳糖肽，深层海洋沉积物中的一类重要的有机质,主要来源于细菌肽聚糖分解。古细菌在深海微生物组中含量丰富，然而，它们在DAA代谢中的作用仍然缺乏研究。这里,我们报道了参与DAA代谢的深海沉积古细菌的生物信息学调查和酶学表征。我们的分析表明，各种古细菌，特别是念珠菌和念珠菌，可以代谢DAA。DAA通过氨基酸消旋酶转化为L-氨基酸（Ala消旋酶，Asp消旋酶和宽底物特异性氨基酸消旋酶），并通过d-丝氨酸氨裂解酶转化为α-酮酸，而含DAA的二-/三-莫罗肽可以被肽酶（二肽酶和D-氨基肽酶）水解。总的来说,这项研究揭示了参与DAA代谢的深海沉积古菌的身份和活动，揭示了深海沉积物中DAAs的矿化和生物地球化学循环。
