Scientific drilling has identified a biosphere in marine sediments ¹ , which contain many uncultivated microbial groups known only by their DNA sequences ^2-4 . Recycling of organic matter in sediments is an important component of biogeochemical cycles because marine sediments are critical for long-term carbon storage ⁵ . Turnover of carbon is hypothesized to be driven by the secretion of enzymes by microbial organisms ^5-7 , which act to break down macromolecules into constitutive monomers that can be transported into cells. As such, the nature of the microbial secretome often influences the function of a community ⁶ . However, the microbial groups involved in this process and the biochemistry they encode is poorly understood. Here, we show that expressed genes from 5 to 159 meters below the seafloor ⁸ (mbsf) encode numerous candidate peptidases and carbohydrate-active enzymes ('CAZymes') ⁹ targeted for secretion. The majority (90-99%) were assigned to Bacteria, of which 12% shared the highest sequence similarity with candidate phyla ^10,11 . The remaining putatively secreted proteins shared highest sequence similarity with archaeal and fungal enzymes, which peak in two redox transition zones ¹² . In the shallower redox zone at 30 mbsf, 20% of the transcripts encoding putative secreted peptidases were assigned to lineages ^7,13,14 of uncultivated Archaea. The target compounds of the predicted secreted proteome show a preference for necromass in the form of microbial cell envelopes as well as plankton and algal detritus. The predicted fungal secreted proteome encodes CAZymes not present in the predicted bacterial or archaeal secreted proteomes, indicating that fungi putatively play a minimal but specialized role in subseafloor carbohydrate recycling.

中文翻译：

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海洋沉积物中的预测微生物分泌物及其目标基质。

科学钻探已经确定了海洋沉积物^1中的生物圈，其中包含许多未经培养的微生物群，这些微生物群仅通过其DNA序列^2-4已知。沉积物中有机物的再循环是生物地球化学循环的重要组成部分，因为海洋沉积物对于长期碳存储至关重要⁵。碳的周转率被认为是由微生物^5-7分泌的酶驱动的，微生物^5-7的作用是将大分子分解为可运输到细胞中的组成型单体。因此，微生物分泌组的性质通常会影响社区的功能⁶。但是，对此过程中涉及的微生物群及其编码的生物化学知之甚少。在这里，我们显示了从海底⁸（mbsf）下方5至159米的表达基因编码了许多靶向分泌的候选肽酶和碳水化合物活性酶（'CAZymes'）⁹。大多数（90-99％）被分配给细菌，其中12％与候选门^10,11具有最高的序列相似性。其余的推测分泌的蛋白质与古细菌和真菌酶共享最高的序列相似性，在两个氧化还原过渡区中达到峰值¹²。在30 mbsf的较浅氧化还原区中，编码假定分泌的肽酶的20％的转录本被分配给谱系^7,13,14未耕种的古细菌。预测的分泌蛋白质组的目标化合物表现出对坏死微生物的偏好，呈微生物细胞包膜，浮游生物和藻类碎屑的形式。预测的真菌分泌的蛋白质组编码在预测的细菌或古细菌分泌的蛋白质组中不存在的CAZymes，这表明真菌在海底碳水化合物的循环中起着最小但专门的作用。