Regulation of CO sub(2) on heterocyst differentiation and nitrate uptake in the cyanobacterium Anabaena sp. PCC 7120

• Published in: Journal of applied microbiology 2005-03, Vol.98 (3), p.693-698
• Main Authors: Kang, R-J, Shi, D-J, Cong, W, Cai, Z-L, Ouyang, F
• Format: Article
• Language: English
• ISSN: 1364-5072; 1365-2672
• DOI: 10.1111/j.1365-2672.2004.02510.x

Aims:The aim of the present investigation was to study the effects of different inorganic carbon and nitrogen sources on nitrate uptake and heterocyst differentiation in the culture of cyanobacterium Anabaena sp. PCC 7120. Methods and Results:Anabaena was cultivated in media BG11 containing combined nitrogen and supplementary NaHCO sub(3) or CO sub(2). Cell growth, heterocyst differentiation, nitrate reductase (NR, EC 1.7.7.2), glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49) and NO[unconverted image] uptake were analysed. The cells cultivated in BG11 sub(0) medium with aeration were taken as reference. Experimental results showed that the differentiation frequency of heterocysts when the cells were cultivated with elevated CO sub(2) was higher than that of the cells grown with air or bicarbonate. Heterocysts appeared unexpectedly when CO sub(2) was introduced into the medium containing nitrate. However, no heterocysts emerged when CO sub(2) was added to medium containing NH[unconverted image] or urea, or when NaHCO sub(3) was supplied to the medium with nitrate. Both nitrate uptake rate and nitrate reduction enzyme activity were depressed by the supplement of CO sub(2) to the culture. The activity of G6PDH was enhanced with the increase in heterocyst differentiation frequency. Conclusion:CO sub(2) might compete with NO[unconverted image] for energy and electrons in the uptake process and CO sub(2) appears favoured. This led to a high intracellular C/N ratio and a relative N limitation. So the process of heterocyst differentiation was activated to supplement nitrogen uptake. Significance and Impact of the Study:This study provided an attractive possibility to form more heterocysts by rapid growth of Anabaena cells cultivated in the medium containing nitrate in order to increase nitrogen fixation and hydrogen production.