Neorhizobium petrolearium OS53 combined with alfalfa (Medicago sativa L.) for remediation of petroleum-contaminated soil

Abstract:

【Objective】 To explore the mechanism of Neorhizobium petrolearium OS53 combined with alfalfa (Medicago sativa L.) in the remediation of petroleum-contaminated soil. 【Methods】 Illumina and Nanopore were employed to sequence the whole genome of N. petrolearium OS53, and the complete genome map of the strain was constructed. Gene prediction and functional annotation were carried out to analyze the genes involved in nodulation and oil degradation. The abilities of strain OS53 to produce indole acetic acid (IAA), secrete siderophore, and solubilize phosphorus and potassium were tested. The activities of urease, dehydrogenase, polyphenol oxidase, and lipase in soil and the levels of chlorophyll, malondialdehyde, proline, soluble protein, soluble sugar, and superoxide dismutase in alfalfa were measured by kits. 【Results】 The genome of strain OS53 consisted of a circular chromosome of 5.56 Mb and two plasmids of 0.92 Mb and 0.38 Mb, respectively, with the G+C content of 60.2%. The genome encoded a total of 6 968 genes. The strain OS53 and N. petrolearium DSM 26482^T showed the 16S rRNA gene sequence similarity of 99.86%, and formed stable branches on the phylogenetic tree, indicating that strain OS53 and N. petrolearium were the same species. Therefore, OS53 was named as N. petrolearium OS53. The strain OS53 had the ability to produce IAA, and the related genes were identified in the genome. After 120 days of remediation of the soil with the initial oil content of (4 403.30±222.10) mg/kg, OS53 and alfalfa showed the remediation efficiency up to 57.53%, which was 44.26%, 41.69%, and 8.84% higher than that of no inoculation of strain OS53, inoculation of OS53 only, and planting alfalfa only, respectively. In the combined remediation system, alfalfa showed elevated the levels of chlorophyll, soluble protein, and soluble sugar and lowered levels of malondialdehyde, proline, and superoxide dismutase, and the soil showed increased activities of polyphenol oxidase, dehydrogenase, lipase, and urease. 【Conclusion】 The strain OS53 had the ability to produce IAA to promote the growth of alfalfa in the petroleum-contaminated soil, which increased the activity of enzymes involved in oil degradation in the soil. Finally, the combined system improved the remediation efficiency of the soil.