Nutrient stress causes akinete differentiation in cyanobacterium Anabaena torulosa with concomitant increase in nitrogen reserve substances

Abstract

Addition of nitrogen source (nitrate), carbon sources (acetate, citrate and fructose), depletion of nutrients (phosphate-free nitrate medium), dilution of medium (2, 4 and 8 times diluted nitrate medium) under unaerated conditions induced akinete differentiation in Anabaena torulosa. Aerated cultures under the same conditions did not differentiate akinetes. The amounts of reserve metabolites--glycogen and cyanophycin (multi-L-arginyl-poly-L-aspartic acid) granule polypeptide (CGP)--were determined in unaerated and aerated cultures, and at different stages of growth and akinete differentiation. The addition of nitrate, acetate, citrate and fructose under unaerated conditions resulted in the accumulation of glycogen and CGP in higher amounts after 4 d (akinete initiation); the CGP content further changed at mature free akinetes phase. Higher accumulation of reserve products was also observed under nutrient deficiency (phosphate-depleted or diluted media) after 4 d of cultivation. Under aerated conditions reserve product accumulation was considerably lower. Thus a low accumulation of reserve products in aerated cultures showed that aeration probably somehow relieves the organism from a nutritional stress.