Diversity and distribution of microorganisms in the sediment of Formosa cold seep in South China Sea

Abstract:

[Objective] Global survey on microbial diversity of cold seep ecosystem pointed out that cold seeps had developed specific types of microorganisms, the main groups were microorganisms involved in methane metabolism, and their distribution were closely linked to the biogeochemical characteristics of the certain cold seep. However, different environmental conditions and small-scale habitats may present inside the cold seep, and studies comparing the microbial diversity and distribution between small-scale habitats in cold seep were lacking. The purpose of this study was to analyze the differences in microbial diversity among different habitats in the Formosa cold seep of South China Sea, and to improve and understand the impact of different environmental factors on the microbial community structure inside cold seep. [Methods] Sediment samples were collected from different habitats including microbial mat area and carbonate rock area from the Formosa cold seep of South China Sea. 16S rRNA genes of archaea and bacteria were sequenced and analyzed. Combined with environmental factors, we compared differences in microbial diversity, and analyzed the impact of environment factors on microbial distribution. [Results] We found that in different habitats in the Formosa cold seep, anaerobic methanotrophic archaea (ANME) was the major archaeal group, accounting for more than 70% of the total relative abundance of archaea; ANME-1b and ANME-2a/b became the main ANME subgroups in microbial mat area, ANME-1b was dominant in the carbonate rock area. Sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB) were the main groups of bacteria in each habitat of cold seep, and they both accounted for more than 20% of the total relative abundance of bacteria. Among them, Desulfosarcinaceaeaccounted for more than 50% of the SRB, and Sulfurovaceaeand Sulfurimonadaceae together accounted for more than 90% of the SOB; other taxa accounting for more than 10% of the bacteria were Gammaproteobacteria and Chloroflexi. The quantitative PCR results of the conserved methane metabolism gene mcrA(methyl coenzyme-M reductase alpha subunit) and the sulfate reduction conserved gene dsrA (dissimilatory sulfite reductase alpha subunit) showed that the copy number of mcrA gene was 10⁹–10¹⁰ copies/g (wet weight), and the copy number of dsrA gene was 10⁸–10⁹ copies/g (wet weight), which were 10–100 times higher than those of the control area located outside the cold seep. The results of community analysis showed that there were significant differences in community structure among different habitats, and the results of multivariate analysis showed that the diversity and distribution of microorganisms in different habitats were significantly associated with the concentration of methane, hydrogen sulfide, sulfate, and dissolved inorganic carbon (DIC). [Conclusion] This research analyzed the microbial diversity of the heterogenous habitats including the microbial mat area and the carbonate rock area in the Formosa cold seep. We found that the main microbial groups were involved in methane (anaerobic methane oxidation) and sulfur (sulfate reduction, sulfur oxidation) metabolism cycle, however, the diversity and distribution of microorganisms in different habitats were significantly different, mainly controlled by environmental factors such as methane, sulfate, hydrogen sulfide and DIC.