Vertical distribution of bacterial, sulfate-reducing and sulfur-oxidizing bacterial communities in sediment cores from freshwater prawn (Macrobrachium rosenbergii) aquaculture pond

Abstract:

The sulfur cycle mediated by microbes in sediments plays an important role in the decomposition of organic matters and nutrient cycling. However, little is known about the microbial diversity and potential regulatory mechanisms involved in sulfate reduction and sulfur oxidation in aquaculture ecosystems. [Objective] To explore the vertical distribution pattern of sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB) and their environmental driving factors. [Methods] In this study, the abundance, diversity and community composition of bacteria, SRB and SOB in surface (0-1 cm), middle (10-11 cm) and bottom (20-21 cm) sediments originated from a freshwater prawn (Macrobrachium rosenbergii) aquaculture pond were investigated by high-throughput sequencing and real-time PCR (qPCR). [Results] The gene copy numbers of bacteria (16S rRNA), SRB (dsrB) and SOB (soxB) showed a trend of dramatic decline from the surface to the middle layer (analysis of variance, P<0.05), but the difference between the middle and bottom layers was not significant (P>0.05). The α-diversity analysis showed that species richness and evenness of three microbial populations both gradually decreased with depth, implying that the microbial sulfur cycling processes mainly occur on the surface layer. The γ-, δ- and β-proteobacteria were the dominant taxa of bacteria, SRB and SOB, respectively. Specifically, SRB was dominated by Desulfobacca and Desulfosarcina; the former has the lowest proportion in the surface layer, while the latter was the opposite. Thiobacillus, as the major genus of bacteria and SOB, was more abundant in the middle layer. Redundancy analysis and Mantel test revealed that the key environmental factors driving the variation of bacterial communities were NO₃^-, SO₄^2-, total organic carbon (TOC) and total organic nitrogen (TON), while the SRB community variation was mainly affected by arsenic (As), TON, NO₃^- and lead (Pb), and SOB responded to the changes in total carbon (TC), NO₂^-, NH₄⁺ and TON. [Conclusion] The abundance, diversity and community structure of bacteria, SRB and SOB in aquaculture pond sediment exhibited distinct vertical distributions, which could be driven by multiple environmental factors.