Shuangshuang Li,Xin Jiang,Chi Zhao,Yuan Ren,Lixin Luo
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.
Pan Ye,Da-Mao Xu,Qing-Jun Meng,En-Wei Cao,Xue-Qiang Zhu
o-Chlorotoluene ( o -CT) is a representative organic pollutant that poses potential risks to ecosystems and human health. Currently, microbial degradation of o -CT remains inefficient and requires improvement. Therefore, in this study, two novel o-chlorotoluene-degrading bacteria— Raoultella planticola OCT-DM2 and Escherichia fergusonii OCT-DM4—were successfully isolated from chemically contaminated soil, and an efficient degrading bacterial community (OCT-MC) was constructed by combining these strains. After optimization, OCT-MC achieved an 80.5% degradation of o -CT under the following conditions: pH 7, 35 °C, 15% (v/v) inoculum, and an initial o -CT concentration of 200 mg L −1 . Gas chromatography-mass spectrometry (GC-MS) analysis identified five key metabolites, based on which a degradation pathway of o -CT by the consortium OCT-MC was proposed. In this pathway, o -CT was initially transformed into toluene via reductive dechlorination, followed by aromatic ring cleavage and oxidative reactions, ultimately leading to complete mineralization. Integrated genomic and transcriptomic analyses further revealed that redox-related genes within OCT-MC acted synergistically to facilitate o -CT degradation. Notably, genes encoding key enzymes, such as benzylsuccinate synthase (BSS), were significantly upregulated at the transcriptional level, providing molecular-level insights into the high degradation efficiency of the OCT-MC consortium. Overall, the constructed consortium OCT-MC exhibits considerable potential for the bioremediation of o-chlorotoluene–contaminated environments and offers a theoretical basis for elucidating the molecular mechanisms underlying chlorinated aromatic hydrocarbon degradation by mixed microbial consortia.
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 E 180 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.
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