Thiosulfate-Dependent Chemolithoautotrophic Growth of Bradyrhizobium japonicum

Abstract

Thiosulfate-oxidizing sox gene homologues were found at four loci (I, II, III, and IV) on the genome of Bradyrhizobium japonicum USDA110, a symbiotic nitrogen-fixing bacterium in soil. In fact, B. japonicum USDA110 can oxidize thiosulfate and grow under a chemolithotrophic condition. The deletion mutation of the soxY 1 gene at the sox locus I, homologous to the sulfur-oxidizing (Sox) system in Alphaproteobacteria, left B. japonicum unable to oxidize thiosulfate and grow under chemolithotrophic conditions, whereas the deletion mutation of the soxY 2 gene at sox locus II, homologous to the Sox system in green sulfur bacteria, produced phenotypes similar to those of wild-type USDA110. Thiosulfate-dependent O 2 respiration was observed only in USDA110 and the soxY 2 mutant and not in the soxY 1 mutant. In the cells, 1 mol of thiosulfate was stoichiometrically converted to approximately 2 mol of sulfate and consumed approximately 2 mol of O 2 . B. japonicum USDA110 showed 14 CO 2 fixation under chemolithotrophic growth conditions. The CO 2 fixation of resting cells was significantly dependent on thiosulfate addition. These results show that USDA110 is able to grow chemolithoautotrophically using thiosulfate as an electron donor, oxygen as an electron acceptor, and carbon dioxide as a carbon source, which likely depends on sox locus I including the soxY 1 gene on USDA110 genome. Thiosulfate oxidation capability is frequently found in members of the Bradyrhizobiaceae, which phylogenetic analysis showed to be associated with the presence of sox locus I homologues, including the soxY 1 gene of B. japonicum USDA110.

Production of Hydrogen Gas from Light and the Inorganic Electron Donor Thiosulfate by Rhodopseudomonas palustris

“…Cells grew with 2 mM thiosulfate and 20 mM bicarbonate with a generation time of 41.5 Ϯ 1.4 h under nitrogen-fixing conditions. Cells were sensitive to concentrations of thiosulfate above 4 mM and grew considerably more slowly, as has been reported previously (22). The pH of the media did not change during the course of the growth experiments.…”

“…R. palustris has been shown to grow photoautotrophically with thiosulfate as an electron source and bicarbonate as a carbon source (22,31,32). The genomes of strain CGA009 and other Rhodopseudomonas strains have homologs of the well-characterized sox gene cluster of Paracoccus pantotrophus, which encodes a multiprotein complex that oxidizes thiosulfate to sulfate within the periplasm (20,25,27).…”

Evidence for Niche Partitioning Revealed by the Distribution of Sulfur Oxidation Genes Collected from Areas of a Terrestrial Sulfidic Spring with Differing Geochemical Conditions

“…Many laboratory studies of bacterial genera that utilize the PSO pathway have been noted to prefer thiosulfate in laboratory studies over other reduced sulfur compounds (66)(67)(68). However, organisms having the branched pathway can also oxidize thiosulfate, and it is likely that the Thiobacillus soxB genes found downstream alongside the PSO pathway soxB genes could be utilizing thiosulfate as a substrate.…”

Microbial diversity and impact on carbonate geochemistry across a changing geochemical gradient in a karst aquifer

“…Thiobacilli are perhaps the beststudied sulfur-oxidizing bacteria (Friedrich et al, 2005). In contrast, potential heterotrophic and chemoorganotrophic indicator taxa in freshwater wells correlated to dissolved oxygen and included the Caulobacterales, which are aerobic, oligotrophic aquatic bacteria with a high degree of metabolic versatility (Boone et al, 2001), Sphingomonadales, which have wide metabolic capabilities (Frederickson et al, 1995), and Rhizobiales, which are ecologically diverse, important in biofilm formation under oxic and anoxic conditions, and are even capable of oxidizing reduced sulfur (Masuda et al, 2010). Other groups include the Pseudomonadales, which are classic examples of respiring chemoorganotrophs with simple nutritional requirements (Spiers et al, 2000), and Burkholderiales, which are metabolically versatile chemoorganotrophs also capable of N 2 fixation or denitrification (Saito et al, 2008).…”