Biostimulants promote biodegradation of n-hexadecane by Raoultella planticola: Generation of lipopeptide biosurfactants

Adding biostimulants is an effective means to improve the degradation efficiency of refractory organics such as petroleum hydrocarbons, and the mechanisms of biostimulants varies from their types. In this study, n-hexadecane was used as the target pollutant to explore the effects of different kinds of biostimulants on the degradation ability of Raoultella planticola. The results showed that sodium gluconate had the most remarkable enhanced effect with an increase of 241.7% within 10 days. Moreover, R. planticola was stimulated by sodium gluconate to secrete biosurfactants and it was confirmed as a non-ionic lipopeptide by structural characterization. Most biosurfactants existed in intracellular and the emulsion index E180 was 58.33%. The addition of the extracted biosurfactants as a biostimulant was validated and found to increase the degradation rate by 341.2% within 6 days. RNA sequencing (RNA-seq) and real-time quantitative PCR (RT-qPCR) were used to reveal the molecular basis of biosurfactants secretion and the results showed the up-regulation of genes for fatty acid and lipopeptide synthesis with the addition of sodium gluconate. In conclusion, this paper demonstrates that sodium citrate, seignette salt, sodium succinate, and sodium gluconate all had a good enhanced effect on R. planticola, and first reported that the promoting effect of sodium gluconate was mainly accomplished by stimulating R. planticola to produce biosurfactants. Direct use of inexpensive biostimulants to stimulate indigenous microorganisms to improve their degradation ability provides an economical idea for the remediation of petroleum hydrocarbon pollution, which will have great application prospects. [Display omitted] •Sodium gluconate increased R. planticola degradation of n-hexadecane.•Sodium gluconate stimulated R. planticola to produce biosurfactants.•The biosurfactants are non-ionic lipopeptide and mainly existed in intracellular.•The enhancement effect of lipopeptides on n-hexadecane degradation was 341.2 %.•RNA-seq and RT-qPCR revealed the production of biosurfactants.