Growth Performance and Akinete Formation of N2- fixing Cyanobacteria

Abstract

Six isolates of soil isolated cyanobacteria were selected to study on growth characteristic and akinete formation. The tested isolates were evaluated in BG₁₁ nitrogen depleted medium under 4,000 lux of light  intensity at 25 °C . Growth performances were evaluated within 12 hours  intervals for 48 hours and at 3, 6, 12, 18 and 21 days after inoculation. The results indicated that dry biomass of cyanobacteria dramatically   increased within 18 days and decreased thereafter. Significant differences on dry biomass were not found among the tested cyanobacteria. The chlorophyll and protein contents of most cyanobacteria continously increased by  cultivation period. The maximum cell number (10⁹ cell ml^-1)  of Nostoc sp. 6CCR1-1 was obtained within 12 days while the others at  18-21 days. The most interesting point of view of this study was the akinete formation of   the Nostoc sp. 6CCR1-1 cultivated in BG₁₁ with  5,10 and 15 mg l^-1 of  phosphorous under light intensity of 2,000 and 4,000 lux. Akinete formation of cyanobacteria was found significantly higher under cultivation in  the medium containing 15 mg. l^-1 of phosphorous and light intensity of 4,000 lux.  At the same time of akinetes increment, the heterocyst cells were  found decreasing. This evidence indicated   that low requirement of nitrogen for growth of cyanobacteria was observed during the vegetative cells being developed to be akinetes.