Santosh Bhargava

Aims: To investigate the effect of NaCl stress on parent Nostoc muscorum and its spontaneously occurring mutant clone showing resistance to growth inhibitory action of NaCl in terms of various physiological parameters. We have further analyzed the role of iron uptake systems in providing a resistant phenotype. Place and Duration of Study: Division of Microbiology, Department of Botany, Government Motilal Science College, Bhopal 462008 (M.P.) India. This work was carried out between August 2021 to May 2022. Methodology: We have examined the various physiological parameters viz. growth, specific growth rate, photosynthetic O₂ evolution, and nitrogenase activity as per the prescribed protocol. Further, DNA microarray analysis was carried out using the Agilent platform. Results: NaCl stress adversely affected growth, photosynthetic O₂ evolution, and nitrogenase activity of the wild-type Nostoc muscorum, while NaCl-resistant mutant remains unaffected under a given stress. Microarray data analysis identified 24 ORF related to the uptake of iron with fold regulation ≥2 in the mutant strain. These ORFs belonging to the ABC-type ferric iron transporter that plays a significant role in the iron acquisition were identified in the mutant strain. Conclusion: The mechanism of iron homeostasis in the NaCl-resistant mutant has been explained. The results presented are essential to explain the regulatory role of the iron uptake system in stressed conditions.

The interactions of bicarbonate (HCO3¯) and different nitrogen sources in the non-diazotrophic cyanobacterium Spirulina platensis in terms of pigments content, photosynthetic O2 evolution, Ca++-dependent ATPase activity and cytochrome c oxidase activity were examined in the present investigation. The cyanobacterium was acclimated to 300 mol m-3 HCO3¯-concentrations in the growth medium containing no nitrogen. The addition of different nitrogen sources in the growth medium resulted in further acclimatization up to 400 mol m-3 HCO3¯. This finding revealed that nitrogen sources incorporated into necessary metabolites, nitrogen storage material and photosynthetic pigments as well. The combined transport of HCO3¯and nitrogen sources ultimately resulted in gradual increase in the examined parameters in order of NO3¯<NH4+<urea. Nitrate and ammonium assimilating enzymes i.e., Nitrate Reductase (NR) and Glutamine Synthetase (GS) were also examined in graded concentration of HCO3¯ and the findings suggested that both the enzymes showed higher activity in the medium containing higher HCO3¯ concentration this suggested that the activity of these enzymes closely linked with carbon fixation. Further, we examined the Ca++-dependent ATPase activity and cytochrome c oxidase activity in the presence of graded concentration of HCO3¯. The enzyme was more active in the presence of high HCO3¯ concentration; the co-existence of NADPH further enhances the enzyme activities. The use of such cultural practices would help in mass production of biopigments on industrial scale and would paved the way for the development of new technology for CO2 fixation using the solar light as the energy source.

The cyanobacterium Nostoc muscorum is able to utilized proline and glycine-betaine as a nitrogen source under unstressed growth conditions. This cyanobacterium when grow in modified Chu No. 10 medium (without Na⁺) unable to utilized proline and glycine-betaine as a nitrogen source. Spontaneously occurring mutant clones defective in Na⁺ transport (Na⁺-R) was isolated and analyzed for proline and glycine-betaine utilization. The mutant phenotype showed normal heterocyst frequency and nitrogenase activity even in the medium containing 1 mM proline or 1 mM glycine-betaine, indicates the role of Na⁺ for proline/glycine-betaine uptake. The Na⁺-R mutant showed 100% survival at pH 11 and was simultaneously able to uptake and utilize proline/glycine-betaine at higher alkaline pH. This indicates that proline and glycinebetaine uptake systems are more efficient at higher alkaline pH. Since, the hypersaline environments are rich in Na⁺ contents and have alkaline pH, therefore it is suggested that the origin and evolution of specific compatible solutes may not depend only on the osmoregulatory role they play, but also on the other ecological factors operating simultaneously in the organism’s niche.

In the parentNostoc muscorum an active proline oxidase enzyme is required to assimilate exogenous proline as a fixed nitrogen source. Cyanobacterial mutants, resistant to growth inhibitory action of proline analogue L-azetidine-2-carboxylate (Ac-R), were deficient in proline oxidase activity, and were over-accumulators of proline. Proline over-accumulation, resulting either from mutational acquisition of the Ac-R phenotype, or from salinity-induced uptake of exogenous proline, confirmed enhanced salinity/osmotic tolerance in the mutant strain. The nitrogenase activity and photosynthetic O₂ evolution of the parent were sensitive to both salinity as well as osmotic stresses than of Ac-R mutant strain. In addition, the mutation to Ac-resistant phenotype showed no alteration in salinity inducible potassium transport system in the cyanobacterium.