Inoculum pretreatment affects bacterial survival, activity and catabolic gene expression during phytoremediation of diesel contaminated soil

Plant–bacteria partnership is a promising approach for remediating soil contaminated with organic pollutants. The colonization and metabolic activity of an inoculated microorganism depend not only on environmental conditions but also on the physiological condition of the applied microorganisms. This study assessed the influence of different inoculum pretreatments on survival, gene abundance and catabolic gene expression of an applied strain (Pantoea sp. strain BTRH79) in the rhizosphere of ryegrass vegetated in diesel contaminated soil. Maximum bacterium survival, gene abundance and expression were observed in the soil inoculated with bacterial cells that had been pregrown on complex medium, and hydrocarbon degradation and genotoxicity reduction were also high in this soil. These findings propose that use of complex media for growing plant inocula may enhance bacterial survival and colonization and subsequently the efficiency of pollutant degradation.

► Inoculum growth medium affects bacterial colonization and metabolic activity.
► Starvation and acclimation of inocula did not affect colonization and activity.
► Bacterial inoculation enhanced hydrocarbon degradation and toxicity reduction.
► Hydrocarbon degradation was correlated with gene abundance and gene expression.
► LB-grown bacterial cells exhibited maximum hydrocarbon degradation.