Enhancing Benzo[a]pyrene Degradation by Pantoea dispersa MSC14 through Biostimulation with Sodium Gluconate: Insights into Mechanisms and Molecular Regulation

Abstract

We investigated biostimulation as an effective strategy for enhancing the degradation efficiency of recalcitrant organic compounds, with MSC14 (a novel polycyclic aromatic hydrocarbon degrading bacterium Pantoea dispersa MSC14) as the study material. Here, we investigated the impact of sodium gluconate on MSC14-mediated degradation of B[a]p. This study focused on the application of sodium gluconate, a biostimulant, on MSC14, targeting Benzo[a]pyrene (B[a]p) as the model pollutant. In this study, the novel PAHs-degrading bacterium P. dispersa MSC14 demonstrated the capability to degrade 24.41% of B[a]p after 4 days. The addition of the selected sodium gluconate stimulant at a concentration of 4 g/L stimulated MSC14 to degrade 54.85% of B[a]p after 16 h. Intermediate metabolites were analyzed using gas chromatography-mass spectrometry to infer the degradation pathway. The findings indicated that sodium gluconate promoted the intracellular transport of B[a]p by MSC14, along with the secretion of biosurfactants, enhancing emulsification and solubilization capabilities for improved B[a]p dissolution and degradation. Further analysis through transmission electron microscopy (TEM) and scanning electron microscopy (SEM) revealed the formation of a biofilm by MSC14 and an increase in flagella as a response to B[a]p stress. Transcriptome profiling elucidated the interplay of quorum sensing systems, chemotaxis systems, and flagellar systems in the degradation mechanism. Additionally, the study uncovered the molecular basis of B[a]p transport, degradation pathways, metabolic changes, and genetic regulation. In summary, the addition of sodium gluconate promotes the degradation of B[a]p by P. dispersa MSC14, offering the advantages of being rapid, efficient, and cost-effective. This research provides an economically viable approach for the remediation of petroleum hydrocarbon pollution, with broad potential applications.

Keywords: Benzo[a]pyrene; Pantoea dispersa MSC14; biodegradation; sodium gluconate.

Figure 1

Screening of biostimulants.

Figure 2

(a) The optimal concentration of sodium gluconate on enhancing the ability of MSC14 to degrade B[a]p: the red bars presents the degradation rate of MSC14 to 20 mg/L B[a]p at different sodium gluconate concentrations after 4 days; (b) the optimal culture time of sodium gluconate on enhancing the ability of MSC14 to degrade B[a]p.

Figure 3

Metabolic pathways of B[a]p degradation by MSC14 as inferred from intermediate metabolites.

Figure 4

TEM (Left) and SEM (Right) scan for bacterial morphology. (A,D): blank group (the natural growth state of MSC14 without B[a]p stress); (B,E): control group (growth state of MSC14 under B[a]p stress); (C,F): Experimental group (growth state of MSC14 under B[a]p stress after adding sodium gluconate).

Figure 5

Analysis of surfactants in MSC14 products. (A) MSM+B[a]p; (B) MSM+ sodium gluconate; (C) MSM+B[a]p+sodium gluconate.

Figure 6

Transcriptional basic characteristics. Control represents the control group, SG represents the experimental group supplemented with sodium gluconate. (a) Statistics of the number of DEGs; (b) Venn diagram of inter-group expression levels: Analysis illustrates the overlap in gene expression between the experimental group treated with sodium gluconate and the control group during the degradation of B[a]p by MSC14. The brown area represents a total of 3998 genes expressed in common between the two groups. The experimental group (orange) and the control group (green) each have 4 and 2 uniquely expressed genes, respectively; (c) KEGG annotation classification of DEGs; (d) KEGG pathway enrichment analysis of DEGs; (e) RNA-seq and RT-qPCR. Figure 6 was created with biorender.com.

Figure 7

DEGs analysis of MSC14 stimulated by sodium gluconate. The genes highlighted within the red boxes in the figure indicate upregulated genes, while those within the blue boxes represent downregulated genes, the blue box represents substances related to metabolism, The brown box represents amino acids, Enlarged illustration of the Electron transport chain in the lower-right quadrant of the image. Figure 7 was created with biorender.com.

Figure 8

Regulation of MSC14 QS system stimulated by sodium gluconate. The genes highlighted within the red boxes in the figure indicate upregulated genes, while those within the blue boxes represent downregulated genes.