Abstract
Microbial community growth efficiency, the ratio of production to substrate assimilated, could provide insights into carbon flow among microbes and the regulation of marine biogeochemical cycles. However, by far microbial metabolic characters were largely undetermined in the deep hadal trench. Here, the structural and metabolism characteristics of microbial communities in five different trenches were investigated using Illumina high-throughput sequencing and quantitative PCR, as well as incubation with the 3H-leucine incorporation method and electron transport system. The community structure and diversity in the trenches located in different hemispheres were significantly different, with significantly higher of diversity and gene abundance appear in the northern and southern hemispheres, respectively. Depth, TOC and TP were identified as key factors. Cooperative relationship existed among different microbial groups as demonstrated by the co-occurrence network and Pearson correlation analysis. The respiration rates were significantly higher in the northern hemisphere than those in the southern hemisphere under atmospheric pressure. The prokaryotic growth efficiencies (PGE) were significantly higher under atmospheric pressure than under high hydrostatic pressure, this negative effect possibly because carbon flow was more inclined to maintain respiration under high hydrostatic pressure. This study represented the first comprehensive investigation of the microbial community structure and metabolic characteristics of sediments in different trenches, providing a preliminary insight into the processes and efficiency of microbial-driven carbon cycles in the deep biosphere.