Diversity of nitrogen-fixing cyanobacteria under various ecosystems of Thailand: I. Morphology,physiology and genetic diversity

The diversity among 853 isolates of nitrogen-fixing cyanobacteria obtained from soil samples collected from different ecosystems including mountainous, forest and cultivated areas in the central, northern and northeastern regions of Thailand was examined. Most isolates showed slow growth rate and had filamentous, heterocystous cells. The percentage of heterocysts in the filaments of different isolates varied from 8.3 to 9.6. Only a few strains showed high nitrogen-fixing potential, while most of the strains exhibited low capacity for nitrogen fixation. Anabaena and Nostoc were the dominant genera among these isolates. One hundred and two isolates were randomly selected from this diverse collection to determine the extent of genetic diversity on the basis of DNA fingerprinting using the PCR method. Based on the PCR products obtained by using a combination of three primers, all strains could be distinguished from one another. When a subset of 45 isolates of Nostoc and a subset of 44 isolates of Anabaena were further analysed by PCR, a wide range of diversity was observed within each of these genera.