Calcium-induced physiological and biochemical changes in cyanobacterium Nostoc MAC

Calcium (Ca²⁺) induced changes in growth, heterocyst differentiation, nitrogenase activity, NO^-₃ uptake, NO^-₂ efflux and Ca²⁺ ATPase activity have been studied in the wild type Nostoc MAC (Het^- Fox^-) and its revertant (Het⁺ Nif⁺, R₁, R₂ and R₃) mutant strains. Growth, NO^-₃ uptake NO^-₂ efflux and Ca^2+- ATPase activities of the wild type Nostoc MAC and its revertant (R₁, R₂ and R₃) mutant strains increased with increase in Ca²⁺ concentration (0-0.5 mM) being maximum at 0.2mA/ Ca²⁺. Similarly, heterocyst differentiation and nitrogenase activity in the revertant (R₁,R₂ and R₃) mutant strains of the wild type Nostoc MAC also increased in response to Ca²⁺ and attained their maximum level at 0.2mM Ca²⁺. In contrast, 0.13mM Ca²⁺ which is being used in the growth medium for routine culturing of Nostoc MAC cells could support only lower growth, heterocyst differentiation, nitrogenase activity, NO^-₃ uptake, NO^-₂ efflux and Ca²⁺-ATPsC activities as compared to 0.2mM Ca²⁺. The cultures devoid of Ca²⁺ on the other hand, showed lowest growth, heterocyst differentiation, nitrogenase activity, NO^-₃ uptake, NO^-₂ efflux and Ca²⁺-ATPaSe activities. The results suggest that (i) 0.2 mM Ca²⁺ is well suited for the maximum growth, heterocyst differentiation, nitrogenase activity, NO^-₃ uptake and NO^-₂ efflux activities in the wild type as well as its revertant mutant strains instead of 0.13 mM Ca²⁺ which is generally being used for the routine culturing of the Nostoc MAC and its revertant mutant strains; (ii) Ca²⁺ appears to have a catalytic role in aerobic nitrogen fixation; and (ii) Ca²⁺ induced physiological and biochemical changes seem to be due to hange in ATP level.