Retrieving sulfur in thiosulfate bio-oxidation: indigenous consortium vs. its dominant isolate Ochrobactrum sp.

Abstract

Sulfur compounds such as thiosulfate are among contaminants with undesirable effects on ecosystems. Sulfur-oxidizing bacteria (SOB) can metabolize these compounds into less pernicious products such as elemental sulfur (S0). In this study, products distribution of thiosulfate bio-oxidation with emphasis on S0 was investigated in shake flasks (SFs) and 1 L stirred bioreactor (SB) using an indigenous SOB consortium. Enrichment of original cells taken from Atashkoh soil resulted in complete oxidation of 3000 ppm thiosulfate and 14% S0 formation as compared to 45% oxidation of original cells. The agarose plate method was selected to preserve this enriched-consortium due to the retrieval of more sulfur (30% in SF). Oxidation of 3000 ppm thiosulfate in SB resulted in 35.2% S0 formation and noticeably a higher thiosulfate depletion rate of 1 compared to 0.2 mmol S L−1 h−1 in SF. Complete oxidation of higher levels of thiosulfate (4000–6000 ppm) was achieved in SB and S0 was reclaimed by a maximum of 40% at 6000 ppm thiosulfate. The dominant strain was isolated and identified by 16S rRNA as Ochrobactrum sp. PN1. Although thiosulfate oxidation by this isolate was quite similar to the consortium, S0 formation was higher (195 mg S L−1) by the consortium compared to the isolated strain (138 mg S L−1). Our enriched SOB consortium was therefore well capable of partial oxidation of thiosulfate into S0, a less polluting intermediate product with versatile applications.