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Isolation and partial characterization of NaCl‐tolerant mutant strain of Anabaena variabilis with impaired glutamine synthetase activity
Author(s) -
Chauhan V.S.,
Singh S.,
Pandey P.K.,
Bisen P.S.
Publication year - 1999
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/(sici)1521-4028(199909)39:4<219::aid-jobm219>3.0.co;2-4
Subject(s) - nitrogenase , anabaena variabilis , mutant , wild type , heterocyst , biochemistry , biology , cyanobacteria , glutamine synthetase , chemistry , nitrogen fixation , glutamine , bacteria , amino acid , gene , genetics
NaCl‐tolerant mutant of diazotrophic cyanobacterium Anabaena variabilis has been isolated by N‐methyl‐N‐nitro‐N‐nitrosoguanidine (NTG) mutagenesis and selection for NaCl resistance. The effect of NaCl (300 m M ) on growth, heterocyst differentiation, nitrogenase, GS, NR, NO 3 — and NO 2 — uptake was studied by maintaining wild‐type A. variabilis as reference. The NaCl‐tolerant mutant grew reasonably well both in presence and absence of NaCl. It also produced more heterocysts and exhibited greater nitrogenase than its wild‐type counterpart in N 2 ‐medium without NaCl. Exposure of wild‐type to NaCl (300 m M ) for 7 days resulted a significant inhibition of growth and heterocyst differentiation with reduced nitrogenase activity. These activities were, however, significantly stimulated by NaCl in NaCl‐tolerant mutant. GS activity in NaCl‐tolerant mutant was reduced to about 50% causing liberation of ammonia in the external medium. No ammonia was however, liberated by wild‐type having normal GS activity, suggesting a metabolic linkage between GS (ammonia assimilation or release) and nitrogenase in NaCl‐tolerant mutant. GS activity in wild‐type was inhibited by NaCl, however, no such inhibition by NaCl was recorded in GS activity of NaCl‐tolerant mutant. Untreated cells of NaCl‐tolerant mutant showed greater levels of NO 3 — and NO 2 — uptake as compared to its wild‐type, which were further increased after NaCl‐treatment. In contrast, NaCl‐treatment to wild‐type cells resulted in stimulation of NO 3 — and NO 2 — uptake systems, however, it also led to almost complete inhibition of NR activity. This suggests that although wild‐type take up NO 3 — and NO 2 — more rapidly in response to NaCl stress, it could not metabolize these due to NaCl‐caused inhibition in NR and GS systems. Thus, NaCl‐caused impairment in nitrogen metabolism may be one of the reasons for reduced growth of wild‐type under NaCl stress.