Résumé
Our investigation aimed to utilize physiological attributes and molecular tools for distinguishing the toxic strain of Microcystis from other non toxic strains, belonging to the same genus. Physiological characterization of five Microcystis isolates indicated that the toxic strain (M1) exhibited significantly higher pigment accumulation (phycocyanin: 54.20 µg ml-1; allophycocyanin: 18.2 µg ml-1) and sugar content (74.25 µg ml-1), which may be providing a competitive advantage for successful colonization and proliferation. Profiling using repeat sequence primers (STRR, Hip) was helpful in distinguishing different strains (M1-M5) and HIP TG profile was unique to M1. SDS-PAGE profile of the five strains indicated the presence of a unique band (25kDa) in M1. The combined use of SDS-PAGE and HipTG profiles can help in providing distinct fingerprint for the toxic strain, which can be useful in its identification.
Résumé
Anabaena oryzae ARM 570 was examined for its growth (chlorophyll and protein), heterocyst frequency, nitrogenase (acetylene reduction) activity, ammonia excretion, and glutamine synthetase and nitrate reductase in response to two levels of urea-N vis-à-vis N2-N. Growth of cyanobacterium increased with duration of incubation. Reduction in heterocyst frequency (40%) was observed at 30 ppm of urea-N, whereas at 60 ppm of urea-N, filaments were completely devoid of heterocysts and no nitrogenase activity was observed. Maximum excretion of ammonia occurred at 30 ppm of urea-N, which was concomitant with minimum glutamine synthetase activity. These results suggested that A. oryzae could be effectively utilized in cyanobacterial biofertilizer programme even in the presence of combined nitrogen, for improving N-budget in rice cultivation.