Abstract
Iron is essential for growth of most organisms, including cyanobacteria, a ubiquitous and ecologically important group of microorganisms in nature. The present study was initiated to investigate the effects of iron starvation on the growth, frequency of heterocysts (the sites for nitrogen-fixation), photosynthetic pigments and photosynthesis in the filamentous, nitrogen-fixing cyanobacterium Nostoc punctiforme ATCC 29133. Iron starvation was achieved in cyanobacterial cultures by growing them in medium free of combined nitrogen containing 2,2’dipyridyl (a high affinity iron-chelator) without any addition of iron source. Compared to iron-sufficient control cultures, the iron-starved cultures showed decrease in growth determined for 15 days. The reduction in growth was coupled with a decreased heterocyst (N2-fixation sites) frequency and the number of cells per filament measured after 2 and 4 days of iron-starvation. Similarly, a considerable drop in the concentration of photosynthetic pigments such as, phycocyanin and chlorophyll a were also noticed in iron-starved cultures. Carotenoid level, however, was higher in iron-starved cultures compared to control. The maximum quantum efficiency of photosystem II photochemistry indicating the photosynthetic efficiency was severely affected in iron-starved Nostoc punctiforme ATCC 29133. Overall, the results presented in this study suggest that deficiency of iron negatively impacts growth, photosynthesis and perhaps nitrogen-fixation in the cyanobacterium N. punctiforme ATCC 29133. Given the role of cyanobacteria in biofertilizer technology, it is suggested that iron bio-availability in agricultural fields may strongly impact the biofertilizer potential of diazotrophic cyanobacteria. Therefore, efforts to improve biofertilizer potential of cyanobacteria may be directed towards identifying strains which can better adapt to iron deficiency.
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