Isolation and Characterization of Obtained Azospirillum and Phosphorus Solubilizing Bacteria from Rhizosphere of Barnyard Millet

Abstract

This study aimed to isolate and characterise Azospirillum and phosphate-solubilising bacteria from the rhizosphere of barnyard millet cultivated in Kolhapur district, Maharashtra, India. Twenty rhizospheric soil samples were collected from Hatkanangale, Karveer, Kagal and Shirol tehsils. Azospirillum and phosphate-solubilising bacteria were isolated by serial dilution and pour plate techniques using nitrogen-free bromothymol blue medium and Pikovskaya’s agar medium, respectively. Four Azospirillum isolates and four phosphate-solubilising bacterial isolates were obtained and evaluated for morphological, cultural and biochemical characteristics. All Azospirillum isolates were Gram-negative and produced white subsurface pellicles on semi-solid nitrogen-free bromothymol blue medium, with vibroid and rod-shaped cells observed among the isolates. All phosphate-solubilising bacterial isolates were Gram-negative and rod-shaped, while colony colour and form varied among isolates. Biochemical testing showed differences among the isolates in methyl red reaction, indole production, gelatine liquefaction, hydrogen sulphide production, oxidase activity and starch hydrolysis, whereas catalase activity was positive in all isolates. All phosphate-solubilising bacterial isolates formed clear halo zones on Pikovskaya’s medium, indicating phosphate-solubilisation activity under the experimental conditions. The recorded solubilisation index ranged from 1.05 to 3.80. These findings document morphological and biochemical variation among Azospirillum and phosphate-solubilising bacterial isolates obtained from the barnyard millet rhizosphere in the sampled areas of Kolhapur district.