A STUDY ON THE GROWTH AND SOME PHYSIOLOGICAL CHARACTERISTICS OF ANABAENA SPIROIDES ISOLATED FROM LAKE ERHAI

In recent years, Lake Erhai is experiencing a transition from the mesotrophic to eutrophic condition and cyanobacterial blooms have a rapid increase in the lake. In this study, the dominant species from the bloom of Lake Erhai, Anabaena spiroides, was isolated and purified. The growth and physiological characteristics of an Anabaena spiroides strain under different environmental conditions were studied to evaluate the influence of environmental factors on Anabaena bloom formation, and the growth was determined by cell biomass and relative growth rate. The results showed that the Anabaena spiroides strain had the best growth at temperature of 25 degrees C, light intensity of 30 mu E/m . s and pH of 8.0-10.0 and under the contents of nitrogen 1.5mmol/L and phosphorus 12 mu mol/L. The activities of nitrate reductase (NR) and alkaline phophatase (APA), which indicate metabolism of nitrogen and phosphorus, were measured with different concentrations of nitrogen and phosphorus. NR activity of the Anabaena spiroides strain increased with the raising of nitrogen concentration when nitrogen supply level was low (0-0.36 mmol/L). But the activity of NR was related to the growth under the condition of rich nitrogen supply (0.36-6 mmol/L), i.e. the better strain' s growth, the higher NR activity: APA activity of the Anabaena spiroides strain largely depended on the concentration of phosphorus. APA activity was lower with more phosphorus supply. And Nitrogen did not play an important role in the activity change of APA when phosphorus supply was rich. In addition, it was observed that the Anabaena spiroides strain could grow with low concentration of nitrogen or phosphorus. This may he related to special regulatory mechanism of nitrogen fixing and phosphorus utilizing of Anabaena