Conversion of methane-derived carbon and microbial community in enrichment cultures in response to O2 availability

Wei, Xiao-Meng; He, Ruo; Chen, Min; Su, Yao; Ma, Ruo-Chan

Conversion of methane-derived carbon and microbial community in enrichment cultures in response to O2 availability

2016

Wei, Xiao-Meng | He, Ruo | Chen, Min | Su, Yao | Ma, Ruo-Chan

Methanotrophs not only play an important role in mitigating CH₄ emissions from the environment, but also provide a large quantity of CH₄-derived carbon to their habitats. In this study, the distribution of CH₄-derived carbon and microbial community was investigated in a consortium enriched at three O₂ tensions, i.e., the initial O₂ concentrations of 2.5 % (LO-2), 5 % (LO-1), and 21 % (v/v) (HO). The results showed that compared with the O₂-limiting environments (2.5 and 5 %), more CH₄-derived carbon was converted into CO₂ and biomass under the O₂ sufficient condition (21 %). Besides biomass and CO₂, a high conversion efficiency of CH₄-derived carbon to dissolved organic carbon was detected in the cultures, especially in LO-2. Quantitative PCR and Miseq sequencing both showed that the abundance of methanotroph increased with the increasing O₂ concentrations. Type II methanotroph Methylocystis dominated in the enrichment cultures, accounting for 54.8, 48.1, and 36.9 % of the total bacterial 16S rRNA gene sequencing reads in HO, LO-1, and LO-2, respectively. Methylotrophs, mainly including Methylophilus, Methylovorus, Hyphomicrobium, and Methylobacillus, were also abundant in the cultures. Compared with the O₂ sufficient condition (21 %), higher microbial biodiversity (i.e., higher Simpson and lower Shannon indexes) was detected in LO-2 enriched at the initial O₂ concentration of 2.5 %. These findings indicated that compared with the O₂ sufficient condition, more CH₄-derived carbon was exuded into the environments and promoted the growth of non-methanotrophic microbes in O₂-limiting environments.

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