Enterobacter sp. as a Two-in-One Stress Buster and Plant Growth Promoter in Rhizosphere of Pigeonpea

Bioinoculants have emerged as an eco-friendly, long term and sustainable alternative to chemical fertilizers, which have been established to adversely affect the ecosystem and human health. The objective of the present study was to study the impact of bioinoculants (individually and in combination) on the stress-busting community of ACC deaminase producers in the rhizosphere of pigeonpea (Cajanus cajan), as a part of risk assessment monitoring of the amendments. ACC deaminase is a pivotal plant growth promoting (PGP) property that aids the plant to encounter biotic and abiotic stresses. It specifically reduces the elevated levels of stress ethylene produced in a plant when it encounters any stress. To achieve this objective samples were taken from rhizospheres of C.cajan, from a plant growth experiment. Upon enumeration of ACC deaminase producing bacteria, treatment with chemical fertilizer was found to have a negative impact on the abundance of putative ACC deaminase positive bacteria, whereas the bioinoculants showed a positive impact. The isolates thus obtained were first screened quantitatively for ACC deaminase activity and subsequently for other desirable PGP properties, including salt tolerance. A potent isolate, which exhibited phylogenetic affiliation with Enterobacter sp., was shortlisted for plant growth experiment in vitro, and in field conditions for validation of their performance under salinity stress. Further, denaturing gradient gel electrophoresis and Illumina sequencing was performed for analysis of the impact of such an amendment on rhizospheric microbial community structure and function. Confirmation of ACC deaminase producing ability of the strain to be responsible for stress mitigation was performed by generation of ACC deaminase mutants and subsequent application in plant growth experiment. The polyphasic study comes up with an efficient ACC deaminase producing strain exerting multiple benefits towards plant growth promotion, hence opens up venues for its successful application in fields under stresses.