Unique deep-sea bacterial assemblages thriving on different organic matters delivered via in-situ incubators

Abstract Background The transport of organic matters to the deep sea constantly occurs in global oceans and in accompany with simultaneous microbial remineralization. However, little is known about the impact of fast sinking organic complex on oceanic deep ecosystem and its interactions with microbes throughout the process of sinking and settling on the sea bottom. In this report, to observe the response of indigenous microorganisms to the newly input of organic matters, we developed a series of deep-sea in-situ incubators loaded on the seabed and seamount with various organic substrates of plant and animal origins. Results The bacterial diversity at the OTU level varied in accordance to organic substrates and geographic locations, but the functional groups are generally similar. The bacteria of Marinifilaceae were revealed as the key member; in addition, other key decomposers including Spirochaetaceae, Psychromonadaceae, Vibrionaceae, Moritellaceae, and Fusobacteriaceae were also recruited in most assemblages with varied abundance accordingly. Interestingly, nitrogen fixation inside the assemblages occurred in the process of polysaccharide decomposing. The microbial co-occurrence analysis revealed that nutrient availability and energy transfer determine relationships cooperation or competition. Within the assemblages stimulated by substrates short of nitrogen sources, the microbial network was dominated by cooperative relationships, whereas competition relationships overwhelmed the communities thriving on proteinous substrates. Conclusions These in-situ observations revealed a unique bacterial assemblage in decomposing diverse newly input organic matters, which may constitute the microbial pumps involved in carbon, sulphur, and nitrogen cycles in oceanic interior.