Concomitant colonization of nifH positive endophytic Burkholderia sp. in rice (Oryza sativa L.) promotes plant growth

Six diazotrophic bacteria were isolated from surface-sterilized roots of rice variety HUR-36, which is grown with very low or no inputs of nitrogen fertilizer. Out of six bacteria one isolate, RREM25, showed appreciable level of nitrogenase activity, IAA production, and Phosphate solubilization ability, and was further characterized with a view to exploiting its plant growth promoting activity. Based on 16S rRNA gene sequence analysis, this isolate was identified as Burkholderia cepacia. Diazotrophic nature of this particular isolate was confirmed by Western blot analysis of dinitrogenase reductase and amplification of nifH. Microscopic observation confirmed colonization of gfp/gusA-tagged RREM25 in the intercellular spaces of cortical as well as vascular zones of roots. Inoculation of RREM25 to rice plants resulted in significant increase in plant height, dry shoot and root weight, chlorophyll content, nitrogen content and nitrogenase activity. Plant growth promoting features suggest that this endophytic bacterium may be exploited in rice cultivation after a thorough and critical pathogenicity test.