Nitrogen metabolism, artificial association study in two cyanobacterial isolates and assessment of their potential as biofertilizer

Two strains of cyanobacteria, viz. Nostoc ANTH and Mastigocladus sp, were isolated from local separate temperature zones of Meghalaya, India. Both the strains showed preference for different temperatures for optimum growth [45°C for Mastigocladus sp.(thermophile) and 25°C for Nostoc ANTH (mesophile)]. The addition of nitrogen sources in the growth media (nitrate, ammonia and glutamine) supported their better growth but repressed heterocyst development and nitrogenase activity. Nitrate and nitrite uptake rates, NR and NiR activities increased by NO3 and decreased by NH4 + in Nostoc ANTH. However, such effects were only partial in Mastigocladus sp. The presence of fixed nitrogen sources in the media led to decreased GS activity and repressed methylammonium uptake in both the strains. Glutamine uptake was substrate inducible, energy-dependent and required de novo protein synthesis. Artificial association studies revealed successful establishment of association of rice roots with both cyanobacteria, including prolonged association of Mastigocladus sp. at high temperature (~45°C). Little modifications in growth temperature and growth media led to profuse akinete differentiation in target cyanobacteria. The replacement of normal cells by akinetes as field inoculants might have profound biotechnological implications in future biofertilizer programme.