Ecophysiology of iron-oxidizing Zetaproteobacteria in an iron oxyhydroxide mound in a shallow marine environment at Satsuma Iwo-jima, Japan.

Abstract:

The Satsuma Iwo-Jima is a small volcanic island located 40 km south of the Kyusyu Island, Japan. In the Nagahama Bay of the island, venting hydrothermal fluids from iron oxyhydroxide mounds on the seafloor. Using a light microscopy, numerous twisted stalk structures in the deposits were observed, suggesting the presence of neutrophilic iron-oxidizing microbial communities. Sequencing of 16S rRNA gene-tagged fragments followed by correlation analysis showed that iron-oxidizing Zetaproteobacteria inhabit the iron deposits in the vicinity of anaerobic iron-reducing bacteria, indicating the occurrence of iron cycling mediated by the microbial ecosystem. We successfully identified Zetaproteobacteria cells using CARD-FISH technique at the different depths of the cored sample, suggesting that the number of Zetaproteobacteria cells and the frequency of the twisted stalk structures are not always consistent. In stalk-abundant horizons that harbor relatively small Zetaproteobacteria populations, accumulation of polyphosphate within Zetaproteobacteria cells was clearly observed. This indicates that Zetaproteobacteria physiologically store energy and phosphorus substrates during the active iron oxidation. In marked contrast, in other horizons with fewer stalks and large populations of Zetaproteobacteria, polyphosphate was rarely observed in the cells, suggesting that Zetaproteobacteria have already used up the intracellular reservoir of energy and phosphorous substrates, and the iron-oxidizing activity is most likely lower than those cells inhabiting the redox interface.