Rapid organic carbon oxidation by sulfate- and Fe(III) reduction coupled to enhanced bacterial diversity in vegetated intertidal mud flats of the Ganghwa

Abstract

The objective of this study was to elucidate microbial community structure associated with the sulfate- and Fe(III) reduction in an unvegetated mud flat (UMF) and a vegetated mud flat (VMF) of the Ganghwa intertidal sediments, Korea. Sulfate- and Fe(III) reduction together comprised 105% and 72% of C oxidation at the UMF and VMF, respectively. Depth-integrated sulfate reduction rates at the VMF (63 mmol m-2d-1) were 3.5 times higher than at the UMF (18 mmol m-2d-1), and dissimilatory Fe(III) reduction rates were 5 times higher at the VMF (507 mmol m-2d-1) than at the UMF (103 mmol m-2d-1). Cloning and sequencing of 16S rRNA gene sequences retrieved in clone libraries from 0-1 cm and 5-6 cm depth (rhizosphere) intervals revealed that clones related to δ-Proteobacteria, including major groups of the sulfate- and Fe(III) reducing bacteria, comprised the largest fraction (25%). Diverse phylotypes related to sulfate-reducing bacteria (Desulfobacterium, Desulfobulbus, and Desulfosarcina) were retrieved from the VMF rhizosphere, whereas only a single Desulfobacterium clone type was observed at a comparable depth (5-6 cm) at UMF. In addition, clone sequences affiliated with Fe(III)/So reducing bacteria (Desulfuromonas/Pelobacter) comprised a large percentage (56.2%; 18 among 32 clones) of the clone library from the VMF rhizosphere. Overall results indicated that dense vegetation supplies organic C substrates and electron acceptors to the rhizosphere, thereby supporting enhanced C respiration by diverse groups of sulfate- and Fe(III) reducing bacteria at the VMF.2