Diazotrophic activity and ferric phosphate mineralizing ability in estuarine sulfate reducing bacteria

Abstract

Twenty strains of sulfate reducing bacteria were isolated from water and sediments of Cochin backwaters, India. Five of them were identified as <i>Desulfovibrio disulfuricans</i> and fifteen as <i>Desulfotomaculum orientis</i>. All the <i>Desulfovibrio</i> were isolated from sediments whereas <i>Desulfotomaculum</i> was present in both water and sediment. All the bacteria grew at <i>p</i>H of slightly alkaline reaction and lowered the <i>E</i>_h from -105 to -270 m V of the growth medium. Complete reduction of sulfate to sulfide by the bacteria was evidenced by blackening of Postgate culture media. All isolates were able to fix nitrogen in anaerobic N-free modified Postgate broth. In addition to nitrogen fixing ability, 5 of the <i>Desulfotomaculum</i> and 3 of the <i>Desulfovibrio</i> were able to produce soluble phosphorus in growth medium from insoluble FePO₄. A scheme for FePO₄ mineralization in marine and estuarine sediments has been proposed.