Characterization of Fe(III)-Reducing Enrichment Cultures and Isolation of Enterobacter sp. Nan-1 from the Deep-Sea Sediment, South China Sea

To characterize the Fe(III)-reducing bacteria, enrichment cultures were initiated by inoculating deep-sea sediment from the South China Sea (SCS) into the media with hydrous ferric oxide (HFO) as the sole electron acceptor. As indicated by Meta 16S rDNA Amplicon Sequencing, the microorganisms related to Fe(III)-reduction in the enrichment cultures were mainly Shewanella and Enterobacter. A new facultative Fe(III)-reducing bacterium was obtained and identified as Enterobacter sp. Nan-1 based on its 16S rRNA gene sequence and physiological characterizations. Enterobacter sp. Nan-1 was not only a mesophilic bacterium capable of reducing HFO with a wide range of salinity (4, 34, 40, 50 and 60 g L−1) efficiently, but also a piezotolerant bacterium that can proceed Fe(III)-reduction sustainedly at hydrostatic pressures between 0.1 and 50 MPa using glucose and pyruvate as carbon source. Furthermore, the geochemical characteristics of deep-sea sediment indicated that the microbial metabolism and iron reduction both remain active in the well-developed Fe(III)-reducing zone where the strain Nan-1 was obtained. To our knowledge, Enterobacter sp. Nan-1 could serve as a new applicative Fe(III)-reducing bacterium for future investigation on the iron biogeochemical cycle and diagenetic process of organic matter in the deep-sea environment.