Physiological alterations and regulation of heterocyst and nitrogenase formation in Het(-) Fix(-) mutant strain of Anabaena variabilis |
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Authors: | Singh Bhanumati Chauhan Vinay S Singh Surendra Bisen Prakash S |
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Institution: | (1) Institute of Microbiology and Biotechnology, Barkatullah University, Bhopal 462 026 M.P., India, IN;(2) School of Studies in Botany, Jiwaji University, Gwalior 474 011 M.P., India, IN;(3) Madhav Institute of Science and Technology, Gwalior 474 005 M.P., India, IN |
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Abstract: | Physiological alterations and regulation of heterocyst and nitrogenase formation have been studied in Het− Fix− mutant strain of diazotrophic cyanobacterium Anabaena variabilis. Het− Fix− mutant strain of A. variabilis has been isolated by N-methyl-N′-nitro-N″-nitrosoguanidine (NTG) mutagenesis and was screened with the penicillin enrichment
(500 μg ml−1). Growth, heterocyst differentiation, nitrogenase and glutamine synthetase (biosynthetic and transferase), 14CO2-fixation, nitrate reductase (NR), nitrite reductase (NiR), glucose-6-phosphate dehydrogenase (G6PDH), and isocitrate dehydrogenase
(IDH) activities, and NO3
−, NO2
−, and NH4
+ uptake and whole cell protein profile in different metabolic conditions were studied in the Het− Fix− mutant strain taking wild-type A. variabilis as reference. Het− Fix− mutant strain was incapable of assimilating elemental nitrogen (N2) due to its inability to form heterocysts and nitrogenase and this was the reason for its inability to grow in BG-110 medium (free from combined nitrogen). In contrast, wild-type strain grew reasonably well in the absence of combined nitrogen
sources and also showed heterocyst differentiation (8.5%) and nitrogenase activity (10.8 ηmol C2H4 formed μg−1 Chl a h−1) in N2-medium. Wild-type strain also exhibited higher NR, NiR, and GS activities compared to its Het− Fix− mutant strain, which may presumably be due to acquisition of high uptake of NO3
−, NO2
−, and NH2
+. Wild-type strain in contrast to its Het− Fix− mutant strain also exhibited high level of G6PDH, IDH, and 14CO2 fixation activities. Low levels of G6PDH and IDH activities in Het− Fix− mutant strain further confirmed the lack of heterocyst differentiation and nitrogenase activity in the Het− Fix− mutant strain.
NR, NiR, and GS activities in both the strains were energy-dependent and the energy required is mainly derived from photophosphorylation.
Furthermore, it was found that de novo protein synthesis is necessarily required for the activities of NR, NiR, and GS in
both wild-type and its Het− Fix− mutant strain.
Received: 21 December 2001 / Accepted: 28 January 2002 |
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