“Candidatus Thiovulum sp. strain imperiosus”: The largest free-living epsilon proteobacteraeota Thiovulum strain lives in marine mangrove environment.

A large (47.75±3.56 µm in diameter) Thiovulum bacterial strain forming white veils is described from marine mangrove ecosystem. High sulfide concentrations (up to 8 mM of H2S) were measured on the sunken organic matters (wood/bone debris) in laboratory conditions. This sulfur-oxidizing bacterium colonized such organic matter forming white veil. According to conventional scanning electron microscope (SEM) observations, bacterial cells are ovoid and slightly motile by numerous small flagella present through the cell surface. Intracytoplasmic large internal sulfur granules were shown suggesting a sulphidic-based metabolism. Observations were confirmed by sulfur elemental sulfur distribution detected by energy-dispersive X-ray spectroscopy (EDXS) analysis using environmental scanning electron microscope (ESEM) on non-dehydrated samples. Phylogenetic analysis of partial sequence of 16S rDNA obtained from purified fractions of this -proteobacteraeota strain indicates that this bacterium belongs to the Thiovulaceae cluster and could be one of the largest Thiovulum ever described. We propose to name this species “Candidatus Thiovulum sp. strain imperiosus”.