Morphological and Plant Growth-Promoting Characterization of Bacillus cereus and Pseudomonas aeruginosa Isolated from Groundnut

Abstract

Groundnut (Arachis hypogaea L.) is an important oilseed and food legume crop, and the use of plant growth-promoting rhizobacteria (PGPR) offers a potential sustainable approach for improving crop productivity. The present study was undertaken to characterise two groundnut-associated bacterial isolates, Bacillus cereus and Pseudomonas aeruginosa, based on their morphological and plant growth-promoting characteristics. The isolates were evaluated for phosphate solubilisation, siderophore production, indole-3-acetic acid (IAA) production, ammonia production, protease activity and cellulase activity. Phosphate solubilisation, siderophore production, protease and cellulase activities were assessed qualitatively, whereas IAA and ammonia production were quantitatively estimated. Morphological characterisation revealed that B. cereus was a Gram-positive, rod-shaped bacterium producing irregular, rough, white and opaque colonies, while P. aeruginosa was Gram-negative, rod-shaped and produced circular to irregular, smooth colonies with greenish-blue pigmentation. Both isolates showed positive phosphate-solubilising and siderophore-producing abilities. B. cereus produced 21.43 µg L⁻¹ IAA and 14.20 µg L⁻¹ ammonia, whereas P. aeruginosa produced comparatively higher amounts of IAA (30.20 µg L⁻¹) and ammonia (17.80 µg L⁻¹). B. cereus exhibited protease activity, while both isolates showed cellulase activity. Overall, both isolates demonstrated multiple and complementary plant growth-promoting and extracellular enzymatic characteristics under in vitro conditions. These findings provide a preliminary basis for further evaluation of the isolates under greenhouse and field conditions to determine their potential for improving groundnut growth and supporting sustainable crop production.