Leaf Surface Colonizing Pink Pigmented Facultative Methylotrophs Harnessed for Their Plant Growth Promoting Traits

In this study, pink pigmented facultative methylotrophs (PPFM) were isolated and screened from leaves of commonly grown vegetables and lowland paddy of Assam. A total of 45 PPFM isolates were obtained, out of which 11 isolates were selected on the quantitative estimation of nitrogenase enzyme activity and indole acetic acid (IAA) production. Eleven selected PPFM isolates exhibited in vitro nitrogenase enzyme activity in the range of 0.59-1.30η moles of C₂H₄ mg^-1 protein h^-1, IAA in the range of 3.47-18.66 μg mL^-1 of culture filtrate, gibberellic acid (GA) in the range of 4.81-20.57 μg mL^-1. Three prospective isolates, viz., PPFM4, PPFM10 and PPFM11 indicated both siderophore and hydrocyanic acid production. All PPFM isolates showed varying response to common antibiotics and few could solubilize insoluble phosphorus and zinc. The isolates responded differently to the biochemical tests like casein hydrolysis, nitrate reduction, urease, citrate utilization and starch hydrolysis. Rhizospheric soil analysis for chemical and biological parameters indicated influence of soil parameters on occurrences of PPFM. The research work indicated the occurrence of wide array of PPFM as leaf inhabitants in different vegetable crops and lowland paddy, which possess varied plant growth promoting traits, and thus could be utilized for formulation of bioinoculants.