Identification and characterization of metabolic potential of different strains from genus Rhizobium

Bacteria of the Rhizobum genus form a group of microorganisms existing in the environment in two forms: symbiotic - in the root nodules of Fabaceae sp. plants and free-living, saprophytic in the soil environment. The basic function of Rhizobum sp. in a symbiosis is to reduce nitrogen to ammonia directly assimilated by the plant.

The subject of study was genetic identification and characterization of metabolic activity Rhizobium genus bacteria. The study was conducted on the 16 bacteria strains from the collection of Department of Agricultural Microbiology, Institute of Soil Science and Plant Cultivation in Puławy, Poland. Bacteria strains were isolated from root nodules derived from plans of the genus Trifolium.

Based on the sequencing of PCR products, we found that all strains belong to one species - Rhizobium leguminosarum. The study of metabolic activity was performed using the GEN III BIOLOG system method (Biolog Inc., Hayward, CA, USA). The GEN III microplate contains 94 phenotypic tests: 71 carbon source utilization assays and 23 chemical sensitivity assays. Tetrazolium dyes from the wells of the microplate are used to indicate the use of carbon sources or resistance to inhibitory chemicals by microorganisms. The cell suspensions were inoculated into the GEN III and incubated for 7 days. The subject of the study was to evaluate the ability of strains of Rhizobium leguminosarum bacteria to metabolize three groups of compounds: carbohydrates (CH), amino acids (AA) and fatty acids (FA).

Based on results the heat maps were made and the cluster analysis according to Ward’s method conducted thus illustrating the diversity of strains in terms of the intensity and pace of the individual compounds consumption. Metabolism analysis of all R. leguminosarum strains with the use of GEN III™ plates showed that carbohydrates (CH) were the most intensively utilised group of substrates. Between the Rhizobium leguminosarum strains, there are metabolic differences in terms of the studied features. That may indicate the adaptive capacity of microorganisms to the environmental conditions in which they currently live.