Microbial Community Structure and Metabolic Characteristics in the Sediments of the Five Different Deep Sea Trenches

Yao XiaoHao LiuHongmei Jing^*

• Institute of Deep-Sea Science and Engineering, Chinese Academy of Sciences (CAS), Sanya, China

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 sea trenches. Here, the structural and metabolic characteristics of microbial communities in five different deep sea 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. We found that microbial community structure and functional gene abundance exhibited significant inter-trench variations, indicating that geographic isolation and environmental filters were key drivers of microbial biogeography. Under atmospheric pressure (AP), significantly higher respiration rates in the Mariana (MT) and Yap (YT) trenches than in the Kermadec (KT), Diamantina (DT), and Wallaby-Zenith (WT) trenches showed that higher organic carbon input in the western Pacific supported more active heterotrophic metabolism. Crucially, the consistently lower prokaryotic growth efficiency (PGE) under high hydrostatic pressure (HHP) across all trenches indicated that in situ pressure fundamentally shifted carbon allocation from biomass production to maintenance respiration, drastically constraining deep-sea carbon conversion efficiency. This demonstrated that genomic potential alone was insufficient to predict carbon cycling rates, and direct physiological measurements under in situ conditions were essential for accurate assessment. Our study provided a preliminary insight into the processes and efficiency of microbial-driven carbon cycles in the deep biosphere.