Halo-tolerant rhizospheric Arthrobacter woluwensis AK1 mitigates salt stress and induces physio-hormonal changes and expression of GmST1 and GmLAX3 in soybean

In the present study rhizospheric bacteria were isolated from sand dune-dwelling Artemisia princeps, Chenopodium ficifolium, Oenothera biennis, and Echinochloa crus-galli and evaluated the ability of the bacterial isolates to produce jasmonic acid (JA) and abscisic acid (ABA) under NaCl-induced salt stress. We observed that 7 of 126 bacterial isolates were capable of producing siderophores, gibberellic acid (GA), indole-3-acetic acid (IAA), phosphate solubilisation, organic acids e.g., quinic acid, succinic acid, acetic acid and butyric acid. A bioassay of the seven selected isolates on rice showed that the isolate AK1 significantly promoted rice growth. Moreover, AK1 produced IAA and ABA in broth spiked with elevated levels of NaCl (100mM, 200mM, 300mM, and 400mM). The isolate AK1 was further investigated for plant growth promotion and mitigation of NaCl-induced salt stress in soybean grown under 100mM, 200mM, and 300mM stress. Application of AK1 upregulated the expression of GmLAXs, and GmST genes in plants exposed to salt stress as compared to uninoculated plants. Interestingly, the bacteria-treated soybean showed significant increase in growth attributes with or without salinity stress. The endogenous ABA and JA level of inoculated soybean plants declined under elevated salt stress, thus showing an enhanced stress mitigation. A similar ameliorative trend was observed for total proteins, polyphenol oxidase, and peroxidase activity under saline conditions. The isolate AK1 was identified as Arthrobacter woluwensis AK1 based on its 16S rDNA gene sequencing and subsequent phylogenetic analysis.