Characterisation of Pseudomonas spp. and Ochrobactrum sp. isolated from volcanic soil

Soil bacteria may have properties of plant growth promotion but not be sufficiently beneficial for plants under stress conditions. This challenge has led researchers to extend their searches into extreme environments for potential soil bacteria with multiple plant beneficial traits as well as abiotic stress tolerance abilities. In the current study, an attempt was made to evaluate soil bacteria from an extreme environment, volcano soils, based on plant growth promoting and abiotic stress mitigating characteristics. The screening led to the isolation of eight (NBRISH4, NBRISH6, NBRISH10, NBRISH11, NBRISH13, NBRISH14, NBRISH16 and NBRISH26) bacterial isolates capable of withstanding stresses, namely temperature (up to 45 °C), salt (up to 2 M NaCl) and drought (up to 60% Poly Ethylene Glycol 6000) in vitro. Further, the selected isolates were notable for their in vitro temporal performance with regards to survival (in terms of colony count), phosphate solubilisation, biofilm formation, auxin, alginate and exo-polysaccharide production abilities under abiotic stresses i.e. 40 °C temperature; 500 mM NaCl salt and drought (PEG) conditions. In vivo seed treatments of individual selected bacteria to maize plants resulted into significant enhancement in root and shoot length, root and shoot fresh and dry weight and number of leaves per plant. Overall, the plant growth promoting and abiotic stress tolerance ability was most evident for bacterial isolate NBRISH6 which was identified as an Ochrobactrum sp. using 16S rRNA based phylogenetic analysis.