Evaluation of lipopeptides biosurfactant from Raoultella planticola for bioremediation in n-hexadecane-contaminated soil

Abstract

Biosurfactants combined with bioaugmentation for the remediation of petroleum hydrocarbon-contaminated soils proved to be one of the most effective ways. However, research on lipopeptides combined with bioaugmentation is rare, and the biological mechanisms are undefined. Therefore, the effect of Raoultella planticola and the lipopeptides it produces to restore contaminated soils was investigated using n-hexadecane as a model of petroleum hydrocarbons. After 60 d, n-hexadecane removal rate increased from 31.3% in contaminated soil to 39.9% with R. planticola alone and 59.0% with R. planticola together with 1.0 g intracellular lipopeptide (INLS) and 7.5 g sodium gluconate (SG)/kg dry soil. Meanwhile, the nitrogen and phosphorus components of the soil increased by 13.9% and 8% in the experimental group, respectively. Besides, DHA activity was 6.7 times that of the control group at 28 d, indicating a considerable increase in DHA activity. Microbial community analysis revealed a considerable increase in functional genera of Sphingomonas, Nocardia, Pseudoalteromonas, Povalibacter, Apiotrichum, Pseudallecheria, and Ascodesmis. The amount of fungus in the experimental group was more than 30 times that of the control group after 60 d. Microbial co-occurrence networks showed improved interactions of Firmicutes and Ascomycota, encouraging synergistic cooperation among microbes and thereby accelerating n-hexadecane breakdown. At once, the metabolic pathways ko00071 and ko00980 for n-hexadecane degradation were greatly elevated, indicating that functional genes such as alkane 1-monooxygenase and NADPH-cytochrome P450 reductase were activated. These results implied that combining hydrocarbon-degrading microbial with INLS was a promising bioremediation technique to remove soil petroleum hydrocarbons.