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Regulation of glutamate metabolism in the cyanobiont Nostoc A NTH by nitrogen sources
Author(s) -
Singh Surendra
Publication year - 1993
Publication title -
journal of basic microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.58
H-Index - 54
eISSN - 1521-4028
pISSN - 0233-111X
DOI - 10.1002/jobm.3620330109
Subject(s) - heterocyst , nitrogenase , glutamate synthase , nostoc , biology , biochemistry , glutamate receptor , glutamine synthetase , cyanobacteria , anabaena , glutamate dehydrogenase , nitrogen fixation , glutamine , bacteria , amino acid , genetics , receptor
Growth, heterocyst differentiation, nitrogenase activity and glutamate uptake were studied in the cyanobiont Nostoc A NTH , a free‐living isolate of the liverwort Anthoceros punctatus. Nostoc A NTH grew well in N 2 ‐medium and produced heterocyst and nitrogenase activity whereas NO 3 − ‐ and NH 4 + ‐grown cultures did not show heterocyst differentiation and nitrogenase activity. Also, glutamate inhibited the diazotrophic growth, heterocyst differentiation and nitrogenase activity. However, the availability of NO 3 +and NH 4 +to the glutamate‐medium resulted in the recovery of growth. NO 3 − ‐ and NH 4 + ‐grown cells showed reduced levels of glutamate uptake which further reduced by the supplementation of NO 3 − ‐ and NH 4 +in the reaction mixture during experimentation. These results suggest that in Nostoc A NTH glutamate acts as an inhibitor of heterocyst differentiation and nitrogenase activity rather than as a nitrogen source and that availability of NO 3 − ‐ and NH 4 +alleviates the glutamate toxicity by inhibiting its uptake. This glutamate toxicity may be the reason for the localization of glutamate forming enzyme, glutamate synthase (GOGAT) within vegetative cells and not within heterocysts.