Diversity of Mixotrophic Neutrophilic Thiosulfate- and Iron-Oxidizing Bacteria from Deep-Sea Hydrothermal Vents

At deep-sea hydrothermal vents, sulfur oxidation and iron oxidation are of the highest importance to microbial metabolisms, which are thought to contribute mainly in chemolithoautotrophic groups. In this study, 17 mixotrophic neutrophilic thiosulfate- and iron-oxidizing bacteria were isolated from hydrothermal fields on the Carlsberg Ridge in the Indian Ocean, nine to the gamma-proteobacteria (Halomonas (4), Pseudomonas (2), Marinobacter (2), and Rheinheimera (1)), seven to the alpha-proteobacteria (Thalassospira, Qipengyuania, Salipiger, Seohaeicola, Martelella, Citromicrobium, and Aurantimonas), and one to the Actinobacteria (Agromyces), as determined by their 16S rRNA and genome sequences. The physiological characterization of these isolates revealed wide versatility in electron donors (Fe(II) and Mn(II), or thiosulfate) and a variety of lifestyles as lithotrophic or heterotrophic, microaerobic, or anaerobic. As a representative strain, Pseudomonas sp. IOP_13 showed its autotrophic gowth from 10(5) cells/ml to 10(7) cells/ml;carbon dioxide fixation capacity with the delta 13C(VPDB) in the biomass increased from -27.42 parts per thousand to 3460.06 parts per thousand; the thiosulfate-oxidizing ability with produced SO42- increased from 60 mg/L to 287 mg/L; and the iron-oxidizing ability with Fe(II) decreased from 10 mM to 5.2 mM. In addition, iron-oxide crust formed outside the cells. Gene coding for energy metabolism involved in possible iron, manganese, and sulfur oxidation, and denitrification was identified by their genome analysis. This study sheds light on the function of the mixotrophic microbial community in the iron/manganese/sulfur cycles and the carbon fixation of the hydrothermal fields.

Automated summary

A total of 17 mixotrophic neutrophilic thiosulfate- and iron-oxidizing bacteria were isolated from hydrothermal fields on the Carlsberg Ridge in the Indian Ocean. These bacteria belonged to different taxonomic groups, including gamma-proteobacteria, alpha-proteobacteria, and Actinobacteria. Physiological characterization revealed their versatility in electron donors and various lifestyles. The representative strain, Pseudomonas sp. IOP_13, showed autotrophic growth, enhanced carbon dioxide fixation, increased thiosulfate-oxidizing ability, and decreased iron-oxidizing ability.