ABSTRACT
Rhizobial purine auxotrophs have earlier been shown to be defective in symbiosis, though the exact reason for this failure is not clear. Using various dyes that specifically bind different cell surface molecules, we show that there are multiple changes in the cell surface molecules associated with different purine auxotrophs. Affected molecules in different purine auxotrophs that were tested include (i) acidic exopolysaccharides, (ii) cellulose fibrils, and (iii) beta (1–3) glucans. Our results show that the symbiotic deficiency of purine auxotrophs is likely to be a result of these associated changes on the cell surface.
ABSTRACT
In Rhizobium meliloti, the promoter P1 of the nif HDK operon, and also the promoter P2, have earlier been shown to be active in the bacteria present in alfalfa root nodules, but not in the bacteria grown aerobically in culture. Here we have looked at the expression from P1 and P2 in two non-symbiotic nitrogen-fixing bacteria, Azotobacter vinelandii and Azospirillum brasilense, using constructions in which the promoters are fused upstream of the ß-galactosidase gene. The promoter P1, but not P2, is active in A. vinelandii, while neither P1 nor P2 is active in Azospirillum brasilense.
ABSTRACT
A strain of Rhizobium meliloti has been shown to be capable of growth in the presence of methionine sulphoximine concentrations at least two orders of magnitude higher than that required for the complete inhibition of glutamine synthetase activity. Neither the specific growth rate, nor the nutritional requirements of the organism were affected by methionine sulphoximine in the medium. Rhizobium meliloti appeared to assimilate ammonia via the glutamate dehydrogenase pathway during growth in the presence of methionine sulphoximine. This suggests that Rhizobium meliloti may have some regulatory mechanism controlling ammonia assimilation that is not present in other enterobacteria possessing similar enzymatic machinery.