Salt stress mitigating potential of bacterial endophytes isolated from Moringa oleifera

The current experiment intended to investigate the plant growth-promoting effects of the bacterial endophytes, identified from Moringa oleifera, under salinity stress. These endophytic isolates, Serratia marcescens (KR-27), Klebsiella aerogenes (KL-4), and Lelliottia amnigena (KS-7) were checked for the phosphate solubilization activity, production of indole acetic acid (IAA) and siderophores, employing the quantitative calorimetric techniques. Amongst the tested strains, KS-7 produced substantial amount of IAA while the isolate KR-27 exhibit strong siderophores production and effective phosphate solubilization. Secondly, the effect of endophytic bacterial strains was checked on the rice plants' morphological parameters in vitro. As a result, the endophytes slightly enhanced the growth indices and fresh/dry biomass of the rice plantlets. Furthermore, the biochemical characterization of the rice plants using standard calorimetric assays revealed that the endophytes inoculation substantially enhanced the level of phytohormones; including IAA, gibberellic acid (GA₃), and salicylic acid (SA), while reducing the level of abscisic acid (ABA). The photosynthetic pigments, including chlorophyll a, b, and carotenoids are also elevated, thereby exhibiting the plant growth-promoting effect of the rice plants. Additionally, among the various metabolites, phenolic acid and flavonoids are substantially enhanced, while low level of proline indicates the efficiency of endophytes in the presence of salinity stress. The basic mechanism of endophytes in mitigating salt stress is the regulation of the imbalanced ionic concentrations. Besides, the introduction of the bacterial strains to the growth culture media in the presence of 200 mM NaCl induced the enzymatic antioxidant system of the rice plants. The strains; KS-7 and KR-27 effectively amplified the enzymatic activities of catalase (CAT), ascorbate peroxidase (APX), and glutathione. All these outcomes recommend the applications of newly identified strains of M. oleifera in mitigating salinity stress in sustainable agricultural practices.