Carbon dioxide regulation of autotrophy and diazotrophy in the nitrogen-fixing cyanobacterium Nostoc muscorum

•CO2 regulation of autotrophy and diazotrophy was studied.•Graded concentration of HCO3− alone and in the presence of various nitrogen sources have positive impact on various physiological parameters.•Ca++-dependent ATPase and cytochrome c oxidase activities enhanced in the presence of graded concentration of HCO3−.•Addition of different nitrogen sources has increased only Ca++-dependent ATPase activity.•Presence of NADPH influenced only Ca++-dependent ATPase activity.

To understand how carbon and nitrogen metabolism are regulated in diazotrophically and non-diazotrophically grown cultures of the cyanobacterium Nostoc muscorum, we investigated the role of bicarbonate (HCO3−) in regulating diazotrophy and autotrophy. Results showed that HCO3− concentration up to 12 mol m−3 enhanced growth, specific growth rate, photosynthetic pigments, photosynthetic O2 evolution and nitrogenase activity under diazotrophic growth conditions. The co-existence of different nitrogen sources in the growth medium further accelerate the examined parameters in the order of NO3−