S-34 Enrichment As A Signature Of Thiosulfate Oxidation In The "Proteobacteria"

Kinetics of thiosulfate oxidation, product and intermediate formation, and S-34 fractionation, were studied for the members of Alphaproteobacteria Paracoccus sp. SMMAS and Mesorhizobium thiogangeticum SJT(T), the Betaproteobacteria member Pusillimonas ginsengisoli SBO3, and the Acidithiobacillia member Thermithiobacillus sp. SMMA2, during chemolithoautotrophic growth in minimal salts media supplemented with 20 mM thiosulfate. The two Alphaproteobacteria oxidized thiosulfate directly to sulfate, progressively enriching the end-product with S-34; Delta S-34(thiosulfate-sulfate) values recorded at the end of the two processes (when no thiosulfate was oxidized any further) were -2.9 parts per thousand and -3.5 parts per thousand, respectively. Pusillimonas ginsengisoli SBO3 and Thermithiobacillus sp. SMMA2, on the other hand, oxidized thiosulfate to sulfate via tetrathionate intermediate formation, with progressive enrichment in the end-product sulfate throughout the incubation period; Delta S-34(thiosulfate-sulfate) at the end of the two processes (when no further oxidation took place), reached -3.5 parts per thousand and -3.8 parts per thousand, respectively. Based on similar S-34 fractionation patterns recorded previously during thiosulfate oxidation by strains of Paracoccus pantotrophus, Advenella kashmirensis and Hydrogenouibrio crunogenus, it was concluded that progressive reverse fractionation, enriching the end-product sulfate with S-34, could be a characteristic signature of bacterial thiosulfate oxidation.