Marine ecosystems harbour a wide range of beneficial microorganisms with considerable potential for agricultural applications. This study highlights the plant growth-promoting abilities of the marine bacterium Enterobacter cloacae strain 6nak4, isolated from the Bay of Cambay. The strain is characterized as Gram-negative, non-endospore-forming and exhibits no hemolytic activity, suggesting low pathogenic potential under the conditions tested. Both qualitative and quantitative analyses indicated multiple mechanisms by which bacterium promotes plant growth. These mechanisms included nitrogen-associated metabolic activity as evidenced by nitrate reduction, ammonia production, solubilization of phosphate and potassium, enhancement of zinc availability, and the production of phytohormones, including indole-3-acetic acid (IAA) as well as gibberellic acid (GA₃). In vivo experiments showed that plants treated with strain 6nak4 displayed significantly enhanced vegetative parameters, including 80% increase in height, a 34.05% rise in root hair density, a 17.77% boost in leaf quantity, and 13% increase in branch number compared to untreated controls. In addition, 6nak4-treated plants demonstrated increased levels of chlorophyll-a, chlorophyll-b, carotenoids, flavonoids, and total proteins suggesting enhanced photosynthetic efficiency and energy metabolism. Moreover, treated plants also showed enhanced antioxidant capacity, as evidenced by increased activities of superoxide dismutase (SOD) and peroxidase (POX), along with elevated levels of proline and phenolic compounds. In summary, E. cloacae strain 6nak4 acts as an effective plant growth-promoting marine bacterium (PGPMB), providing significant physiological advantages and representing a potential candidate for sustainable agricultural practices.
Singh et al. (Mon,) studied this question.