PHOSPHOGLUCOSE ISOMERASE MUTANT OF RHIZOBIUM-MELILOTI

A mutant strain of complex phenotype was selected in R. meliloti after nitrosoguanidine mutagenesis. It failed to grow on mannitol, sorbitol, fructose, mannose, ribose, arabitol or xylose, but grew on glucose, maltose, gluconate, L-arabinose and many other carbohydrates. Assay showed the enzyme lesion to be in phosphoglucose isomerase (pgi), and revertants, which were of normal growth phenotype, contained the enzyme again. Nonpermissive substrates such as fructose and xylose prevented growth on permissive ones such as L-arabinose, and in such situations there was high accumulation of fructose 6-phosphate. The mutant strain had about 20% as much exopolysaccharide as the parent. N2 fixation by whole [lucerne] plants was low and delayed when the mutant strain was the inoculant.