Induction of sporulation by sulphate limitation in <i style="">Nostoc ANTH</i>, a symbiotic strain capable of colonizing roots of rice plants

57-62Nostoc ANTH is a symbiotically compatible cyanobacterium that associates with rice plants and carries out associative N2-fixation. Investigations were carried out to induce profuse sporulation in the cyanobacterium for use as inocula in rice paddies. Impacts of pH and temperature changes, addition of various carbon sources and limitation of phosphate and sulphate on akinete formation were studied. Among these, only phosphate and sulphate limitation induced akinete formation in Nostoc ANTH. Under both the conditions all vegetative cells eventually became akinete. However, induction of akinete differentiation was quicker and resulted in more profuse akinetes differentiation in response to sulphate limitation than to phosphate limitation. These akinetes showed long-term viability (upto 5 years) and excellent germination frequency (90-95 %). This is the first report on induction of akinete formation by sulphate limitation