Effects of Mannose on the Growth of N(2)-Fixing Azotobacter vinelandii

Mannose is not a suitable substrate for N(2)-fixing Azotobacter vinelandii. However, when H(2) gas is provided, A. vinelandii can grow mixotrophically with H(2) as the energy source and mannose as the carbon source (T.-Y. Wong and R. J. Maier, J. Bacteriol. 163:528-533, 1985). In this report, seven sugars were used to determine whether A. vinelandii could derive energy from these sugars for mannose utilization. Supplementation of fructose- or galactose-limited medium with mannose did not influence the biomass produced by N(2)-fixing A. vinelandii. The presence of mannose in glucose- or maltose-limited cultures increased cell yield slightly. The addition of mannose decreased the total biomass in the melibiose-limited culture slightly. Mannose was a potent inhibitor of growth when sucrose or turanose was used as the primary sugar. The inhibitory effect of mannose on utilization of sucrose and turanose seems to be related to the energy requirement of the N(2)-fixing processes.