Isolation, molecular identification, and screening of endophytic bacteria Gluconacetobacter diazotrophicus and Herbaspirillum seropedicae from plant root tissues with the capacity for plant growth promoting traits

The microbes that colonize the plant inter or intracellular, referred to as endophytes, establish symbiotic relationships within plant cells, thereby augmenting their resilience to multiple stress factors. In the present study, endophytic bacteria, namely Gluconacetobacter sp. and Herbaspirillum sp., were isolated from the tissues of surface-sterilized roots and stems of two crops: sugarcane and rice. Six endophytic isolates were used for morphological, and biochemical observations. Furthermore, they were screened for plant growth-promoting traits, including phytohormone production, nitrogen-fixing ability, mineral solubilization, biocontrol activity, and stress tolerance capacity. The isolates GA 1 and HS 1 produced a maximum concentration of Indole acetic acid and Gibberellic acid, fixed maximum nitrogen i.e., 85.62 and 32.53 mg of N/g of carbon used, respectively. These two isolates also showed the maximum mineral solubilization zone, inhibition zone against the rice pathogens, ACC deaminase enzyme activity, and tolerance to various stresses viz., salt, thermal, and drought. The efficient isolates GA 1 and HS 1 which were selected based on screening results further examined for molecular characterization by the 16S rRNA gene sequencing method. The isolate GA 1 was identified as Gluconacetobacter diazotrophicus and HS 1 was identified as Herbaspirillum seropedicae. The results of this study demonstrated that these endophytic bacteria are good repositories of plant growth-promoting activity, which should be investigated further.