Mutational Engineering of the Cyanobacterium Nostoc muscorum for Resistance to Growth-Inhibitory Action of LiCl and NaCl

Abstract

The effect of NaCl on two vital processes of cyanobacterial metabolism, viz. N(2) 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 O(2)-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 x 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.

Differential response of NaCl-Resistant mutants of the cyanobacterium Nostoc muscorum to salinity and osmotic stresses

“…The present findings are in agreement with a previous report on osmoregulation of oxygenic photosynthesis and N 2 -fixation (Tel-Or 1980;Bhargava et al 2003).…”

“…Heterocyst frequency, chlorophyll a contents (Mackinney 1941), protein contents (Lowry et al 1951), percentage survival, nitrogenase activity, photosynthetic O 2 evolution and intracellular proline contents were measured as described previously by (Bhargava et al 2003;Bhargava 2005).…”

A Lithium-Sensitive and Sodium-Tolerant 3′-Phosphoadenosine-5′-Phosphatase Encoded by halA from the Cyanobacterium Arthrospira platensis Is Closely Related to Its Counterparts from Yeasts and Plants

“…But, in general, how sulfur metabolism is regulated in response to environmental changes remains largely unknown. Mutants of a cyanobacterial strain resistant to LiCl have been isolated, but the targets of these mutations have never been clearly identified (6). Characterization of enzymes involved in sulfur metabolism could be helpful for the understanding of the regulation of sulfur metabolism in cyanobacteria.…”

Nostoc muscorum: a regioselective biocatalyst for 17-carbonyl reduction of androst-4-en-3,17-dione and androst-1,4-dien-3,17-dione

“…Purification and properties of glycogen isolated from a cyanobacterium, N. muscorum was reported with Chao and Bowen (1971). A mutational engineering of N. muscorum was studied for resistance to growth-inhibitory of LiCl and NaCl (Bhargava et al, 2003). We also reviewed through the literatures the production of numerous enzymes as well as the ability of steroid biotransformations by different microalgae including Nostoc muscorum in our previous paper (Tabatabaei Yazdi et al, 2004).…”