Vertical Stratification of Dissolved Organic Matter Linked to Distinct Microbial Communities in Subtropic Estuarine Sediments.

Wenxiu Wang,Jianjun Wang,Hongmei Chen,Ke Yu,Penghui Li,Chen He,Chuanlun Zhang,Bu Xu,Jianchang Tao,Quan Shi

doi:10.3389/fmicb.2021.697860

Abstract

Dissolved organic matter (DOM) provides carbon substrates and energy sources for sediment microbes driving benthic biogeochemical processes. The interactions between microbes and DOM are dynamic and complex and require the understanding based on fine-scale microbial community and physicochemical profiling. In this study, we characterized the porewater DOM composition in a 300-cm sediment core from the Pearl River estuary, China, and examined the interactions between DOM and archaeal and bacterial communities. DOM composition were highly stratified and associated with changing microbial communities. Compared to bacteria, the amplicon sequence variants of archaea showed significant Pearson correlations (r ≥ 0.65, P < 0.01) with DOM molecules of low H/C ratios, high C number and double bond equivalents, indicating that the distribution of archaea was closely correlated to recalcitrant DOM while bacteria were associated with relatively labile compounds. This was supported by the presence of auxiliary enzyme families essential for lignin degradation and bcrABCD, UbiX genes for anaerobic aromatic reduction in metagenome-assembled genomes of Bathyarchaeia. Our study demonstrates that niche differentiation between benthic bacteria and archaea may have important consequences in carbon metabolism, particularly for the transformation of recalcitrant organic carbon that may be predominant in aged marine sediments.

Highlights

Dissolved organic matter (DOM) consists one of Earth’s largest carbon exchangeable reservoirs, having major significance in biogeochemical cycles
When all the molecules were classified by specific elemental compositions, lignins/carboxyl-rich alicyclic molecules (CRAM)-like structures dominated at all depths (Supplementary Figure 1B), averagely accounting for 69.5% (7.5%)
Dissolved organic matter in sediment porewater is primarily derived from enzyme-mediated hydrolysis and depolymerization of POM and/or lysis of microbial cell components (Burdige and Komada, 2015; Liang et al, 2017)

Summary

Introduction

Dissolved organic matter (DOM) consists one of Earth’s largest carbon exchangeable reservoirs, having major significance in biogeochemical cycles. The decomposition of particulate-attached organic matter to DOM by hydrolysis and depolymerization is a stepwise process and serves as the principal energy and carbon source for benthic organisms. DOM Linked to Microbial Communities (Burdige and Komada, 2015; Mahmoudi et al, 2017). DOM is highly complex in composition and consists of a mixture of organic compounds with different mass size and functionality (Burdige and Komada, 2015; Canuel and Hardison, 2016). The major composition of DOM is uncharacterized due to limitation of extraction and analytical methods. Advanced spectroscopic tools like Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) is capable of resolving thousands of DOM compounds with high mass resolution and accuracy and provides significant insights into the molecular composition of DOM (Oni et al, 2015; Schmidt et al, 2017)

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