Dominance of <i>Sulfuritalea</i> species in nitrate‐depleted water of a stratified freshwater lake and arsenate respiration ability within the genus

<jats:title>Summary</jats:title><jats:p>Facultative autotrophs of the genus <jats:italic>Sulfuritalea</jats:italic> within the class Betaproteobacteria have been predicted to be an important bacterial population in stratified freshwater lakes based on previous PCR‐based studies. Here, we designed a new probe specific for the genus <jats:italic>Sulfuritalea</jats:italic> and performed catalysed reporter deposition‐fluorescence <jats:italic>in situ</jats:italic> hybridisation to enumerate cells of <jats:italic>Sulfuritalea</jats:italic> species throughout the water column in a stratified freshwater lake. The cells stained with the <jats:italic>Sulfuritalea</jats:italic>‐specific probe were detected in all hypoxic water samples collected in different seasons and years. Their abundance ranged from 1.4 × 10<jats:sup>4</jats:sup> to 2.1 × 10<jats:sup>5</jats:sup> cells ml<jats:sup>−1</jats:sup>, corresponding to 0.5–5.5% of the total DAPI‐stained cells and 2.3–15% of the total bacterial cells. A high abundance of <jats:italic>Sulfuritalea</jats:italic> species was recorded in hypoxic water samples without nitrate, which is the only known anaerobic electron acceptor for <jats:italic>Sulfuritalea</jats:italic>. Nitrate‐independent anaerobic respiration was further investigated using a single cultured representative of this genus, and its growth via arsenate respiration was experimentally demonstrated. In conclusion, <jats:italic>Sulfuritalea</jats:italic> species were found to be a major component of the planktonic bacterial community in nitrate‐depleted hypoxic water, where arsenate respiration is one of the possible energy metabolisms of <jats:italic>Sulfuritalea</jats:italic>.</jats:p>