Characterization of free-living cyanobacterial strains and their competence to colonize rice roots

Abstract

A total of 45 cyanobacterial strains isolated from rice fields near Loktak Lake in Manipur, India were tested for their rice root colonization capacity under light and under darkness. Twenty-one of these strains showed significant colonization of rice roots. The average colonization values were 637 and 381 μg chl a g−1 root dry wt in N2 medium and 792 and 451 μg chl a g−1 root dry wt in NO3− medium under light and darkness, respectively. Thus, while the colonization was higher under light and in NO3− medium, there was significant level of colonization under darkness in N2 medium (381 μg chl a g−1 root dry wt). A 16S rRNA gene fragment-based denaturing gradient gel electrophoresis analysis revealed difference in the competence of individual strains to colonize rice roots exposed to individual or mixed population. The colonization pattern of seven strains used in competition experiments was found to be biphasic. A 16S rRNA gene-based phylogenetic analysis revealed high level of molecular similarity among strains of Nostoc and Anabaena.