Mutational Engineering of the Cyanobacterium <Emphasis Type="Italic">Nostoc muscorum</Emphasis> for Resistance to Growth-Inhibitory Action of LiCl and NaCl |
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Authors: | Santosh Bhargava Rishi K Saxena Pramod K Pandey Prakash S Bisen |
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Institution: | (1) Department of Microbiology, Barkatullah University, Bhopal 462026 (M.P.) India, IN;(2) Madhav Institute of Technology and Science, Gwalior 474011 (M.P.) India, IN |
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Abstract: | The effect of NaCl on two vital processes of cyanobacterial metabolism, viz. N2 fixation and oxygenic photosynthesis, was studied in the cyanobacterium Nostoc muscorum grown diazotrophically. An increase in NaCl concentration suppressed the formation of heterocyst and adversely affected the
nitrogenase activity in the parent, whereas in Li+-R and Na+-R mutants NaCl stress did not cause any adverse effect. The rate of photosynthetic O2-evolution was also adversely affected by the NaCl stress, but the magnitude was less than that of nitrogenase activity. L-Proline, the well-known osmoprotectant, provided protection to the cyanobacterium against NaCl stress. The parent strain
utilized L-proline as a nitrogen source and suppressed heterocyst formation and nitrogenase activity, while mutants showed normal heterocyst
frequency and nitrogenase activity. Therefore, it may be that the proline metabolism is altered as a result of mutation. The
intracellular levels of proline in the parent were enhanced about threefold in the medium containing 1 mol m−3 proline, while in mutants there was no significant increase in the intracellular level of proline. In the medium containing
both NaCl and proline, the intracellular level of proline was enhanced in the parent as well as in both mutant strains. This
suggests that the parent strain possessed both normal proline uptake and salt-induced proline uptake systems, whereas the
mutant strains were defective in normal proline uptake and had only salt-induced proline uptake. The over-accumulation of
proline in the presence of NaCl stress is due either to the loss of proline oxidase activity or to the accumulation of exogenous
proline.
Received: 10 July 2002 / Accepted: 13 August 2002 |
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