Temperature induced physiological and biochemical alterations in the paddy field cyanobacterium Anabaena doliolum

346-352Combustion of fossil fuels and resultant emission of carbon dioxide has led to increased global temperature. Since cyanobacteria are an integral component of the paddy field microflora and contribute to nitrogen fixation, increase in temperature may adversely affect the nitrogen dynamics of the soil. Therefore, to understand the physiological and biochemical response of the mesophilic diazotrophic cyanobacterium Anabaena doliolum to elevated temperature, the organism was grown under three temperature regimes 30, 35 and 40°C for 15 days. Exposure of the cyanobacterium to 40°C resulted in severe reduction in growth and cellular constituents as compared to the cells exposed to 35°C. The cyanobacterial cells also showed enhanced production of H2O2 and lipid peroxidation products in response to exposure to elevated temperature. Further, we observed increased activity of superoxide dismutase, catalase and peroxidase in A. doliolum exposed to elevated temperature. Increase in the temperature resulted in enhanced level of non-enzymatic antioxidants such as carotenoid, proline and ascorbate. Although, the number of heterocysts increased in response to temperature, the nitrogenase activity decreased significantly. The results have demonstrated the sensitivity of the cyanobacterium A. doliolum to elevated temperature

Salinity Induced Alterations in the Growth and Cellular Ion Content of Azolla caroliniana and Azolla microphylla

The nitrogen fxing aquatic pteridophyte Azolla is often found in the rice felds and is responsible for maintaining the soil fertility and productivity. Salinity is known to severely afect approximately half of the irrigated lands worldwide. Therefore, in the present study, the salinity stress response in the whole plants, freshly isolated cyanobionts and the roots of A. caroliniana and A. microphylla exposed to 90 mM NaCl for 9 days was evaluated in terms of growth and ion content. Growth of the whole plant was estimated as increment in the dry weight. NaCl (90 mM) inhibited the growth of A. caroliniana and A. microphylla. The root length and the number of roots of A. caroliniana and A. microphylla were estimated and A. microphylla showed signifcant increase in the length and number of roots. Accumulation of Na+, K+ and Ca2+ ions was also estimated in the whole plant, freshly isolated cyanobionts and the roots. The whole plant of A. microphylla accumulated less Na+ and more K+ whereas A. caroliniana accumulated more Na+ and less K+. Roots of A. microphylla accumulated less Na+ as compared to A. caroliniana and the cellular K+ and Ca2+ content was high in the roots of A. microphylla. Differential levels of Na+, K+ and Ca2+ ion accumulation were observed in the freshly isolated cyanobionts. The results showed signifcant genotypic diferences in growth and ion content of the whole Azolla plants and its cyanobionts. These results possibly suggest that A. microphylla and its cyanobionts exhibit better growth potential in response to salinity through efcient maintenance of ion content

An Alkaline Phosphatase/Phosphodiesterase, PhoD, Induced by Salt Stress and Secreted Out of the Cells of Aphanothece halophytica, a Halotolerant Cyanobacterium ▿ †

Alkaline phosphatases (APases) are important enzymes in organophosphate utilization. Three prokaryotic APase gene families, PhoA, PhoX, and PhoD, are known; however, their functional characterization in cyanobacteria largely remains to be clarified. In this study, we cloned the phoD gene from a halotolerant cyanobacterium, Aphanothece halophytica (phoDAp). The deduced protein, PhoDAp, contains Tat consensus motifs and a peptidase cleavage site at the N terminus. The PhoDAp enzyme was activated by Ca2+ and exhibited APase and phosphodiesterase (APDase) activities. Subcellular localization experiments revealed the secretion and processing of PhoDAp in a transformed cyanobacterium. Expression of the phoDAp gene in A. halophytica cells was upregulated not only by phosphorus (P) starvation but also under salt stress conditions. Our results suggest that A. halophytica cells possess a PhoD that participates in the assimilation of P under salinity stress