Effect of diesel contamination on bacterial populations in a pristine soil during rhizoremediation

Abstract Background and aims Contamination of soils with hydrocarbons such as diesel is of major concern as use and transport increases. In order to obtain a better understanding of how soil microorganisms face diesel during rhizoremediation of a natural soil will help us improve remediation processes. Methods We conducted microcosm experiments with a pristine soil contaminated or not with diesel and planted with clover, clover/ryegrass or non-planted controls. We measured the aromatic fraction of diesel by HPLC-DAD along time under the different experimental conditions and determined the bacterial communities in soil and the rhizosphere by amplicon sequencing of the 16S rRNA gene. Results The presence of clover accelerates the disappearance of the aromatic components of diesel but not significantly so. The bacterial diversity is lowered by diesel contamination although this decline is mitigated by the presence of plants. Bacterial community structure is mostly affected by soil type and then by diesel contamination. Actinobacteriota and Gemmatimonadota decline while Firmicutes, Bacteroidota and Proteobacteria increase with diesel contamination and in the rhizosphere. Amplified sequence variants (ASVs) belonging to Novosphingobium and Sphingomonas are especially abundant in diesel contaminated bulk soil and ASVs belonging to Azospirillum , Rhizobium , Ohtaekwangia Faecalibacterium , and Subdoligranulum are especially abundant in diesel contaminated rhizosphere. Conclusion Clover helps dissipate diesel aromatic compounds faster from a pristine soil. Clover and ryegrass mitigate the decline of bacterial diversity in soil due to diesel contamination and certain bacterial taxa which are enriched with the contaminant are identified which may play a role to remediate diesel contamination.