Tetrathionate Disproportionation by Thiomonas intermedia K12

Abstract

Thiomonas intermedia K12, a moderately acidophilic bacterium, which oxidises sulphur compounds, ± exhibited the capability to use tetrathionate under oxic and anoxic conditions. Whereas under oxic conditions, the reduced sulphur tetrathionate compound was oxidised, under anoxic conditions, the organism disproportionated the compound. In both cases, trithionate and sulphate were produced but in different amounts. The results of the tetrathionate degradation experiments under oxic conditions pointed towards a cyclic degradation process with a transient formation of trithionate and sulphate as the final products, similar to the mechanism described for acidophilic sulphur compound oxidising bacteria. The results of the tetrathionate degradation experiments under anoxic conditions hinted to a partial reduction of tetrathionate to thiosulphate and a fractional oxidation to trithionate and sulphate. 4 M tetrathionate were converted to 6 M thiosulphate, 1 M trithionate, 1 M sulphate, and 8 M protons. The DG 0 ' of this reaction was found to be ±16.1 kJ per mol tetrathionate degraded. Additionally, Thiomonas intermedia K12 grew under anoxic conditions with tetrathionate as the sole energy source. The cell numbers increased from 10 5 as the start value to 10 7 /mL at the end. Organic compounds, excluding traces of yeast extract, did not enhance growth. Therefore, it is proposed that tetrathionate disproportionation is a novel lithotrophic metabolism, which allowed Thiomonas intermedia K12 to survive changing conditions of oxygen supply in sulphur-compound-rich environments and even to grow during this reaction. The extensive sulphur compound analysis was carried out by ion-pair chromatography.

Methanogenic Biocathode Microbial Community Development and the Role of Bacteria

“…However, P. limicola does not ferment sugars, amino acids, or aromatic compounds . The EHM-biocathode also had a phylotype related to Thiomonas intermedia strain K12, a species capable of fermenting tetrathionate under anoxic conditions or oxidizing sulfur species under aerobic conditions . A relative, Thiomonas arsenivorans , is known to excrete exopolymeric substances that enhance biofilm stability .…”

“…51 The EHM-biocathode also had a phylotype related to Thiomonas intermedia strain K12, a species capable of fermenting tetrathionate under anoxic conditions or oxidizing sulfur species under aerobic conditions. 52 A relative, Thiomonas arsenivorans, is known to excrete exopolymeric substances that enhance biofilm stability. 53 A total of three phylotypes of γ-Proteobacteria were also observed in the EHM-biocathode, most closely related to Citrobacter amalonaticus, Pseudomonas aeruginosa, and Pseudomona grimontii.…”