Cultured and genetic diversity, and activities of sulfur-oxidizing bacteria in low-temperature hydrothermal fluids of the North Fiji Basin

Abstract

We determined key chemical parameters and thiosulfate oxidation in low-temperature hydrothermal fluids from the North Fiji Basin. In addition, the bacterial diversity (with the main emphasis on sulfur-oxidizing bacteria) was investigated. The hydrothermal fluids had low concentrations of sulfide (up to 50.0 µM) and increased counts of both total bacteria and sulfur-oxidizing bacteria compared to ambient seawater. Pure cultures of bacteria were isolated from these fluids on media suited for autotrophic, and potentially heterotrophic, sulfur-oxidizing bacteria. Evidence for the abundance of α- and γ -Proteobacteria was obtained from identification of isolated pure cultures. A large number of 16S rDNA sequences of these groups were retrieved from environmental DNA. Representatives of the Cytophaga-Flavobacterium phylum were found by denaturing gradient gel electrophoresis (DGGE) and 16S rDNA sequence information of DGGE bands, although these bacteria could not be isolated with the media used in this study. Evidence for the presence of chemolithoautotrophic sulfur-oxidizing bacteria was found by analysis of environmental DNA, using 16S rDNA-specific primers of various groups of chemotrophic sulfur bacteria. They were isolated in low numbers compared to chemoheterotrophic and mixotrophic sulfur-oxidizing bacteria. In addition, the formation of tetrathionate as major oxidation product of thiosulfate added to hydrothermal fluid samples and to pure cultures of new isolates indicates the importance of chemoheterotrophic sulfur-oxidizing bacteria within the warm vent waters investigated during this study.