Paddy seeds bacterization with ACC deaminase producing endophyte Alcaligenes faecalis SSP8 regulates physiology, leaves gas exchange parameters, PSII photochemistry and antioxidant enzymes metabolism in NaCl stressed seedlings

The endophytic microbes play crucial roles to crop development under stress environmental conditions. In this research, 36 endophytic bacterial strains having diverse morphology were isolated from exotic wild plant Croton bonplandianus. The strain SSP8 was selected for experimental study as it efficiently tolerate NaCl (0–1200 mM), produced Indole-3-acetic acid (IAA) (46 μg mL^-1) and 1-amino-1-cyclopropane-1-carboxylate (ACC) deaminase (176.70 nmol α-ketobutyrate mg^-1 protein h^-1). The SSP8 was identified as Alcaligenes faecalis with 16 S r-RNA gene sequencing and submitted to NCBI-USA with accession number OR225818. The A. faecalis SSP8 significantly enhanced paddy seeds germination percentage, seedlings vigour index and vegetative growth parameters under different NaCl (0–180 mM) regimes. The paddy seedlings chlorophyll contents, Chl-a fluorescence transient (PSII photochemistry), leaves gas exchange parameters were significantly enhanced in A. faecalis SSP8+NaCl (0–180 mM) conditions. The oxidative stress biomarkers and antioxidant enzymes activities were significantly declined in A. faecalis SSP8+NaCl (0–180 mM) treated seedlings. In conclusion, based on the above results the paddy seeds bacterization with A. faecalis SSP8 could be a bio-prospective tool to alleviate the NaCl stress and enhance the paddy crop agriculture productivity in salt affected marginal soils.