Abstract
Previous studies of microbial communities in deep-sea hydrothermal ferric deposits have demonstrated that members of Zetaproteobacteria play significant ecological roles in biogeochemical iron-cycling. However, the ecophysiological characteristics and interaction between other microbial members in the habitat still remain largely unknown. In this study, we investigated microbial communities in a core sample obtained from shallow hydrothermal iron-oxyhydroxide deposits at Nagahama Bay of Satsuma Iwo-Jima, Japan. Scanning electron microscopic observation showed numerous helical stalk structures, suggesting the occurrence of iron-oxidizing bacteria. Analysis of 16S rRNA gene sequences indicated the co-occurrence of iron-oxidizing Zetaproteobacteria and iron-reducing bacteria such as the genera Deferrisoma and Desulfobulbus with strong correlations on the sequence abundance. CARD-FISH indicated that the numbers of Zetaproteobacteria were not always consistent to the frequency of stalk structures. In the stalk-abundant layers with relatively small numbers of Zetaproteobacteria cells, accumulation of polyphosphate was observed inside Zetaproteobacteria cells, whereas no polyphosphate grains were observed in the topmost layers with fewer stalks and abundant Zetaproteobacteria cells. These results suggest that Zetaproteobacteria store intracellular polyphosphates during active iron oxidation that contributes to the mineralogical growth and biogeochemical iron cycling.
Highlights
Members of the class Zetaproteobacteria were first found at the Loihi Seamount, Hawaii (Moyer et al, 1995)
In the deep-sea hydrothermal iron-oxyhydroxide deposits, it has been demonstrated that the dissolved oxygen is present but generally lower than that of the surface seawater, e.g., less than 50 μM of oxygen was observed in iron-rich mats around the Loihi Seamount (Glazer and Rouxel, 2009), suggesting that members of the Zetaproteobacteria preferentially inhabit and grow by oxidizing ferrous iron to ferric iron at the sub-oxic redox condition
In the 50 cm-long core sample obtained from shallow hydrothermal iron deposits in the Nagahama Bay, members of the phylum Chloroflexi are the most predominant microbes throughout the core column
Summary
Members of the class Zetaproteobacteria were first found at the Loihi Seamount, Hawaii (Moyer et al, 1995). Ecophysiology of Zetaproteobacteira in Iron Deposits distributed in iron-oxyhydroxide deposits on the plate spreading centers, hot-spot seamounts, and island arcs (Davis et al, 2009; Kato et al, 2009; Forget et al, 2010; Edwards et al, 2011; McAllister et al, 2011; Fleming et al, 2013). These observations strongly suggest that microbial communities involving Zetaproteobacteria play significant ecological roles in biogeochemical iron and other elemental cycles. Ecophysiology and growth/survival strategy of Zetaproteobacteria correlated with other members in the iron-oxidizing microbial ecosystem are still largely unknown
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