A preliminary study of anaerobic thiosulfate-oxidising bacteria as denitrifiers in the Arabian Sea

Abstract

Bacteria which oxidize thiosulfate and reduce nitrate (TONRB) and bacteria which oxidize thiosulfate and denitrify (TODB) sampled at 5-, 100-, 200-and 300-m depths were enumerated in agar shake cultures by colony counting and by applying MPN technique, respectively. Lithotrophic denitrification was generally high at the surface but did not vary much with the distance from shore as indicate by the number of TODB. The number of TONRB shows that nitrate-reduction was much higher at near-shore stations. The low TODB/TONRB ratios at intermediate depths and at 100 m show in particular that the relative abundance of these organisms could be one of the possible reasons for higher nitrite concentrations sometimes reported at these depths. Thiosulfate-oxidizing and simultaneous nitrate-reducing abilities of the isolates indicated that the strains isolated from near shore and surface waters were more active nitrate reducers than their counterparts in offshore or deeper waters. The growth yield values of these organisms ranged from 1.1 to 17.9 mg protein mmol-1 thiosulfate and from 11.7 to 36.3 mg protein mmol-1 sulfide and suggest that they could contribute to chemosynthetic production