TY - JOUR T1 - Genomic and morphologic characterization of a planktonic <em>Thiovulum</em> (<em>Campylobacterota</em>) dominating the surface waters of the sulfidic Movile Cave, Romania JF - bioRxiv DO - 10.1101/2020.11.04.367730 SP - 2020.11.04.367730 AU - Mina Bizic AU - Traian Brad AU - Lucian Barbu-Tudoran AU - Joost Aerts AU - Danny Ionescu AU - Radu Popa AU - Jessica Ody AU - Jean-François Flot AU - Scott Tighe AU - Daniel Vellone AU - Serban M. Sarbu Y1 - 2020/01/01 UR - http://biorxiv.org/content/early/2020/11/04/2020.11.04.367730.abstract N2 - Life in Movile Cave (Romania) relies entirely on primary carbon fixation by bacteria oxidizing sulfide, methane and ammonia with oxygen, nitrate, sulfate, and ferric iron. There, large spherical-ovoid bacteria (12-16 μm diameter), rich in intracellular sulfur globules, dominate the stable microbial community in the surface water of a hypoxic Air Bell. These were identified as Thiovulum sp. (Campylobacterota). We obtained a closed genome of this Thiovulum and compared it to that of Thiovulum ES. The genes for oxidizing sulfide to sulfate are absent, therefore, Thiovulum likely avoids constant accumulation of elemental sulfur either by oxidizing sulfide to sulfite which is then excreted, or via dissimilatory nitrate reduction to ammonia using the formate-dependent nitrite reductase or hydroxylamine oxidoreductase. Thus, Thiovulum, found also in other caves, is likely important to both S and N cycles in subterranean aquatic ecosystems. Additionally, using electron microscopy, we suggest that in absence of motor-like structures along the membrane, the peritrichous flagella-like structures are type IV pili, for which genes were found in both Thiovulum genomes. These pili may play a role in veil formation, connecting adjacent cells. The force exerted by coordinated movement of such pili may partly explain the exceptionally fast swimming of these bacteria.Competing Interest StatementThe authors have declared no competing interest. ER -