First report of Providencia vermicola strains characterized for enhanced rapeseed growth attributing parameters

Ever-increasing prices of synthetic fertilizers in developing countries put a huge burden on farmer community in terms of per unit cost of production. Supplementing chemical fertilizers with bacterial inoculants offers an alternative strategy to sustain yield by reducing cost of produce. Thus, in current study, two Providencia vermicola strains KP-21 and KR-29 were identified through 16S rRNA gene sequence analysis. The KP-21 and KR-29 strains were originally isolated from rhizosphere of rapeseed grown in Peshawar and Rawalakot, respectively. Morphologically, both strains were similar with round creamy colonies, short rod and Gram-negative cells under light microscope. P. vermicola KP-21 was found promising in phosphate soubilization and auxin biosynthesis. Likewise, strain P. vermicola KR-29 was found to be a potential phosphate solubilizer, auxin producer in addition to its considerable acetylene reduction capacity. High performance liquid chromatography (HPLC) analysis revealed that strain KP-21 produced gluconic and lactic acids, while strain KR-29 synthesized gluconic, malic and lactic acids in considerable amounts. Both strains densely colonized rapeseed rhizosphere area as depicted in transmission electron micrographs. Moreover, the strains significantly (P≤0.05) augmented rapeseed root and shoot length, dry weight, and phosphorus contents, while a significant increase in root and shoot nitrogen contents was only recorded in plants inoculated with strain KR-29 as compared to non-inoculated plants. We concluded that P. vermicola strains are being reported for the first time as rapeseed growth promoting agents. In addition, strain KP-21 and KR-29 were prospective PGPR rhizotypes which were recommended to be evaluated further under field conditions comprising of different agro-climatic locations before using them as commercial bio-inoculants.