| Four Sinorhizobium meliloti mutants with IPTG-dependent phenotypes were isolated via random Tn5tac1 mutagenesis. The growth phenotypes of Rm30192 (pheT), Rm30193 (ffh ), and Rm300196 (unmapped) were conditional on the presence of IPTG, while that of Rm30194 was conditional on its absence. The insertion in Rm30194 is upstream of tacA, which appears to be under conditional control of the Tn5tac1 Ptac. While all four strains formed root nodules on alfalfa, Rm300192 and Rm30193 attained only 53% and 36% respectively, of the wild-type shoot dry weight value.; Five previously isolated Tn5tac1 mutants were also characterized. Significantly, Rm30044 (bhbA) was able to use arabinose but not glutamate as sole carbon source, a novel finding. Finally, Rm30047 (gpsA), which lacks NADPH-dependent glycerol-3-phosphate dehydrogenase (G3PDH) activity, was found to have an NADH-dependent G3PDH activity that was repressed by IPTG, possibly due to conditional expression by the Tn5tac1 P tac of genes downstream of gpsA. |
