Effects of Cyanobacteria crude extracts on growth and related physiological activities of Chlorococcum humicola and Chlorella

This, investigation was concerned with studying the effects of the crude extract of four cyanobacteria on the growth and some physiological activities of two unicellular green algae (Chlorella vulgaris and Chlorococcum humicola). Two of these cyanobacteria (Microcystis aeruginosa and Nodularia harveyana) are known to produce toxin, while the other two cyanobacteria (Nostoc linckia and Lyngbya valderianum) are known to produce auxin-like substances. The obtained results indicated, in general, that growth and the studied physiological activities, except amino acids biosynthesis, of both Chlorococcum and Chlorella were inhibited by crude extracts of the two cyanobacteria species Microcystis and Nodularia. The increase in amino acid (free amino acids & proline) biosynthesis recorded for both experimented algae treated by crude extracts of M. aeruginosa and N. harveyana might be attributed to certain defense mechanisms in response to toxin stress. The obtained data concerned with the effects of crude extracts of the two cyanobacteria Nostoc and Lyngbya on the algal species under investigation, revealed that the crude extracts in concentrations 5-15 µg/ml, had stimulatory effects on growth and physiological activities of both algae. The highest concentrations, 20 µg/ml, were inhibitory to growth and all physiological activities except for amino acids which were stimulated