Thiothrix

Abstract

AbstractThi'o.thrix. Gr. neut. n.theîon, brimstone, sulfur (Latin transliterationthium); Gr. fem. n.thrix, hair; N.L. fem. n.Thiothrix, sulfur hair.Proteobacteria / Gammaproteobacteria / Thiotrichales / Thiotrichaceae / ThiothrixGram‐stain‐negative, aerobic, and facultative anaerobic filamentous bacteria that can attach to surfaces. Distribution occurs with the help of gonidia. All species are capable of forming rosettes. Elemental sulfur is stored intracellularly. Nonmotile. Capable of chemolithoautotrophic and heterotrophic growth. Mixed metabolic modes are also observed, but it is not entirely clear if this is chemolithoheterotrophy or mixotrophy. Obligately respiratory metabolism. Molecular oxygen, nitrate, and thiosulfate can be used as terminal electron acceptors. CO2is fixed through the Calvin–Benson–Bassham cycle. Genomes encode all enzymes of the Krebs cycle, except for the canonical malate dehydrogenase (NAD+,mdh, EC 1.1.1.37) which is replaced by malate dehydrogenase (quinone,mqo, EC 1.1.5.4), which donates electrons to the quinone pool. Reduced sulfur compounds are oxidized to sulfate. Hydrogen sulfide is oxidized to elemental sulfur by bacterial sulfide:quinone reductase (Sqr, EC 1.8.5.4) and sulfide‐cytochromecreductase (flavocytochrome c, FccAB, EC 1.8.2.3) enzymes; sulfur then oxidized to (bi)sulfite by dissimilatory sulfite reductase (DsrAB, EC 1.8.99.5), and then to sulfate via the direct route by sulfite dehydrogenase (quinone, SoeABC, EC 1.8.5.6) and the indirect one via sulfate adenylyltransferase (Sat, EC 2.7.7.4) and adenylyl‐sulfate reductase (AprAB, EC 1.8.99.2). Thiosulfate is oxidized through a branched version of the Lu‐Kelly cycle (SoxABXYZ). Mesophilic. Dominant fatty acids are C16:1ω7, C16:0, and C18:1ω7. Known habitats are sulfidic springs and lakes, coastal seawater, sulfidic groundwaters, deep‐sea hydrothermal vents, activated sludge, sewage, and exoskeletons of someCrustacea.DNA G + C content (mol%):49.3–54.9 (genome sequence).Type species:Thiothrix niveaWinogradsky 1888AL(Beggiatoa niveaRabenhorst 1865).