Derepression of Nitrogen Fixation in Desulfovibrio gigas and its Stability to Ammonia or Oxygen Stress in vivo

SUMMARY: Nitrogen fixation (acetylene reduction) by Desulfovibrio gigas was displayed weakly and capriciously in lactate/sulphate media and sequential or continuous diazotrophic cultures were not successfully established. Washed cells from lactate-grown N-limited chemostat populations at 28 °C showed reproducible anaerobic derepression of acetylene reduction, accompanied by limited growth, in low-N buffer, if sodium pyruvate + sodium sulphate were provided. Hydrogenase activity was not affected by the concentrations of acetylene used. Optimum concentrations of cells, pyruvate + sulphate, casein hydrolysate, Na2MoO4 and FeSO4 were established: peak activities of ~10 nmol C2H2 reduced min-1 (mg bacterial protein)-1 occurred with 10% (v/v) C2H2 after about 48 h; Ni2+, Mn2+ or derepression under Ar did not influence activity. NH+ 4 or air prevented derepression. An oxidant, usually sulphate, was essential. Thiosulphate was a poor substitute for sulphate; sulphite was apparently ineffective. Lactate, fumarate or H2 did not replace pyruvate as derepression substrate.

Pyruvate-derepressed populations showed reversible inactivation when exposed briefly to air. Activity was substantially inhibited by 10 or 100μm-NH+ 4, reversibly at low NH+ 4 concentrations.