THE RELATIONSHIP OF BIOMASS, POLYSACCHARIDE AND H-2 FORMATION IN THE WILD-TYPE AND NIFA/NIFB MUTANTS OF RHODOBACTER-CAPSULATUS

The production of biomass, polysaccharide storage material and H-2 from malate was studied in the wild-type and mutants RdcI, RdcII and RdcI/cII of Rhodobacter capsulatus. The mutants are defective in either copy I, copy II or both copies of the nitrogenase genes nifA and nifB. Stationary phase levels of biomass, polysaccharide and H-2 were determined in phototrophic batch cultures grown with 30 mM of D,L-malate and either 2, 5, or 8 mM of ammonium or 7 mM of glutamate. Calculation of the amounts of malate converted into the three products revealed that, at 8 mM of ammonium and 7 mM of glutamate, malate consumption and product formation were balanced. But with decreasing ammonium concentrations malate not converted into biomass was utilized with decreasing efficiency in polysaccharide and H-2 formation. This suggests formation of unknown products at the lower ammonium concentrations. Under conditions of optimal N supply, 80% of the malate not used for biomass production was converted by the wild-type and strain RdcII to H-2 and CO2. Mutant RdcI exhibited slightly decreased H-2 production. The double mutant did not evolve H-2 but accumulated increased amounts of polysaccharide. However, the amounts of polysaccharide were lower than should be expected if all of the spare malate, not utilized by the double mutant for H-2 production, was converted into storage material. This and incomplete conversion of malate into known products at low ammonium supplies suggests that polysaccharide accumulation does not compete with the process of H-2 formation for malate.