Molecular characterization of rhizobial isolates from Sesbania bispinosa

Abstract

Amongst the soil bacteria one unique group, the Rhizobia have a beneficial effect on the growth of plants. The bacterium within root nodules converts atmospheric nitrogen to ammonia and provides organic nitrogenous compounds to the plants. The symbiotic association between rhizobia and leguminous plants is one of the major contributors to the total biological nitrogen fixation, which is an alternative to the use of nitrogen fertilizers that lead to unacceptable pollution levels. Of the different legumes, one well-known legume of Bangladesh, Dhaincha (Sesbania bispinosa) have generally been considered as an important green manure among the farmers. Thus it was important to study the rhizobial isolate of this less studied legume in order to understand its association to increase soil fertility. The test isolates were previously isolated and characterized and identified through biochemical tests. They gave the correct size amplification product for the nifH gene and nodC gene, which indicated their possession of nodulation and nitrogen fixation ability. This was further confirmed when the same isolates was found to produce nodules in plant infection test in the laboratory. Furthermore, the amplification band of nifH gene was observed only in plasmid, further proving that the symbiotic genes might be plasmid borne. Lipopolysaccharide profiling showed variation in some bands indicating certain diversity prevails among the rhizobial isolates with respect to LPS expression. The isolates were observed further and found to be capable of phosphate solubilization. These characteristics made these rhizobia a suitable choice for use as in symbiotic association with Sesbania bispinosa to work as biofertilizer.

Biological Nitrogen fixation (BNF) technology can play an important role in substituting for commercially available N fertilizer. The test isolates from Sesbania sp. can be an environmental friendly solution in the face of N-fertilizer pollution. Thus it’s important to further characterize these isolates in the molecular level to choose the ideal strain of rhizobia for Sesbania bispinosa.