Volatile organic compound pollution caused by toluene has become a global issue. In order to solve this problem, biodegradation of toluene has been applied all over the world. This study investigated the effects of Fe³⁺ on toluene degradation by the Rhodococcus sp. TG-1. The results show that 1 mg L⁻¹ Fe³⁺ increased the degradation rate of 600 mg L⁻¹ toluene from 61.9% to 87.2% at 16 h. The acceleration mechanism of Fe³⁺ was explicated using transmission electron microscope (TEM) and energy-dispersive X-ray spectroscopy (EDX) analyses, coupled plasma optical emission spectroscopy, an enzyme activity assay, and transcriptome analysis. Four genes were detected to be significantly up-regulated under Fe³⁺ induction, suggesting that Fe³⁺ might be implicated in toluene degradation. Meanwhile, Fe³⁺ was a component of the active center of catechol 1,2-dioxygenase (C12O) and significantly improved the enzyme activity of C12O. The mechanism by which Fe³⁺ accelerates toluene degradation was proposed based on the transcription levels of degradation genes and the enzyme activity of C12O. This study provided an improved method for enhancing the degradation effect of toluene and furthered our comprehension of the mechanism of toluene degradation.

Polycyclic aromatic hydrocarbons (PAHs) are a class of persistent organic pollutants composed of two or more fused benzene rings, posing serious threats to ecological environments and human health. Biodegradation is an efficient, economical, and sustainable approach for remediating PAHs pollution. In our previous work, we isolated and characterized a PAH-degrading bacterium, Burkholderia sp. FM-2. FM-2 demonstrated strong tolerance and efficient degradation capacity toward various PAHs, achieving 81.98% degradation of 2 mM phenanthrene within 3 days, and over 58% degradation of 2 mM fluorene, dibenzofuran, and dibenzothiophene under the same conditions. Through combined genomic and transcriptomic analyses, a putative PAH degradation gene cluster was identified in the FM-2 genome. Phylogenetic and domain architecture analyses were conducted on seven oxygenase genes within the cluster. Using AlphaFold 3, we predicted the three-dimensional structure of the downstream transport protein OmpW and proposed a potential transmembrane channel for PAHs uptake. To eliminate the phenanthrene degradation intermediate 1-hydroxy-2-naphthoic acid, a genetically engineered strain FM-2::nahG was constructed by heterologous expression of the salicylate hydroxylase gene (nahG). The modified strain completely abolished the accumulation of 1-hydroxy-2-naphthoic acid and achieved complete mineralization of phenanthrene. This study not only reveals the molecular basis of PAHs degradation in Burkholderia sp. FM-2 but also demonstrates the potential of metabolic engineering to enhance biodegradation ability, providing a promising microbial candidate for the bioremediation of PAH-polluted environments.

Aniline and crude oil are common environmental pollutants that present a significant risk to both the ecological and human health environments. The implementation of efficacious bioremediation strategies is imperative for the elimination of these contaminants. In this study, a bacterial strain designated DH-2 was isolated from soil contaminated with aniline. The strain was identified as belonging to the genus Rhodococcus. The optimal conditions for the growth and aniline degradation by strain DH-2 were determined to be pH 8.0 and 35 °C, respectively. Under these conditions, the degradation rate of aniline at a concentration of 1000 mg/L exceeded 90% within 36 h. Even in the presence of 4% NaCl, the degradation rate remained above 60%. HPLC–MS analysis revealed that the aniline degradation pathway of strain DH-2 follows the catechol pathway. Additionally, strain DH-2 is capable of utilizing crude oil as the sole carbon source, achieving a degradation rate of 91.0% for 2% crude oil concentration within 4 days. In soil modeling experiments, strain DH-2 was observed to degrade aniline and crude oil under triple stress conditions, including 1000 mg/L aniline, 2% crude oil, and 20 mg/L Fe(II) or Pb(II). Complete degradation of aniline and crude oil was achieved after 3 days and 12 days, respectively. The addition of Fe(II) or Pb(II) ions was found to enhance the degradation ability of DH-2. These results demonstrate that strain DH-2 is an extremely effective biodegradable strain, with potential applications in the remediation of environments contaminated with aniline and crude oil, even in the presence of heavy metals.

This study investigated the fluorene degradation ability and metabolic pathway of Burkholderia sp. FM-2. The FM-2 demonstrated a 72.16 % degradation rate of 300 mg/L fluorene over a period of three days. HPLC-MS analysis identified major metabolites including 9-fluorenol, 9-fluorenone, and phthalate. The impact of heavy metals on fluorene degradation was also assessed. FM-2 exhibited strong tolerance to heavy metals, with a minimum inhibitory concentration (MIC) of 1000 mg/L for Cd(II). The study found that the removal rate of 100 mg/L Cd(II) was 70.42 %, and it was observed that this concentration had a slightly enhancing effect on fluorene degradation. Proteomic analysis revealed that multicopper oxidases and proteins involved in metabolic pathways for instance glutathione metabolism, sulfur metabolism were up-regulated under Cd(II) stress, suggesting potential mechanisms for Cd(II) tolerance and co-metabolism. Moreover, the effect of biochar on FM-2 for the remediation of co-contamination with fluorene and Cd(II) was evaluated. After immobilizing FM-2 with modified biochar (BC-BW), the degradation efficiency of fluorene significantly increased from 72.58 % to 84.93 % and the removal efficiency of Cd(II) increased from 70.42 % to 84.50 %. In the contaminated soil remediation experiment, the removal rates of fluorene and Cd(II) by the immobilized bacteria were 72.59 % and 66.67 %, respectively. These findings demonstrate that modified biochar enhances the remediation efficiency of FM-2 in co-contaminated soils. This study provides theoretical support and practical guidance for the application of biochar-based immobilization techniques in microbial remediation of complex polluted environments.

Various surfactants have been applied for the remediation of polycyclic aromatic hydrocarbon (PAH)-contaminated environments, but their roles in bioremediation remain controversial. This study focused on rhamnolipid (a typical surfactant) and Burkholderia sp. FM-2 (a high-efficiency phenanthrene-degrading bacterium), investigating its effects on phenanthrene solubilization and biodegradation by analyzing cell surface characteristics and gene expression differences. Results showed that low concentrations of rhamnolipid (20–120 mg/L) promoted phenanthrene degradation, while high concentration (400 mg/L) exerted an inhibitory effect. At 20–56 mg/L, rhamnolipid altered the bacterial surface morphology and functional groups, facilitated lipopolysaccharide release, enhanced cell surface hydrophobicity, and increased zeta potential. When the rhamnolipid concentration was 20 mg/L, the phenanthrene degradation rates of cytoplasmic enzymes, periplasmic enzymes, and extracellular enzymes produced by the bacterium reached over 98% after 15 days of enzyme system culture, demonstrating its role in promoting enzyme production and activity. Transcriptomic analysis revealed that 56 mg/L (1 CMC) rhamnolipid enhanced degradation through multi-pathway regulation of gene expression: upregulating the gene encoding protocatechuate 3,4-dioxygenase to strengthen benzene ring cleavage; increasing the expression of genes related to ABC transporters and protein transport to promote phenanthrene transmembrane transport; and activating genes involved in metabolic processes such as pyruvate metabolism and the tricarboxylic acid (TCA) cycle to enhance central carbon metabolic flux. This regulatory mode optimizes energy supply and redox balance, and indirectly improves phenanthrene bioavailability by modulating membrane structure and function.

In this study, Bacillus amyloliquefaciens SQ-2, previously isolated from a commercial watercress paste, was investigated for its potential in promoting rice growth in Pb/Al-contaminated acidic soil, especially when used in conjunction with corn straw biochar. Firstly, the physiological properties of rice were enhanced, with the activities of catalase and superoxide dismutase increasing by 162.5% and 162.9%, respectively. Additionally, the total phenolic and chlorophyll contents of rice increased by 17.6% and 83.7%, respectively. Secondly, the nutrient content of the rice rhizosphere soil was improved. In particular, nitrate nitrogen, available potassium, and sucrase were enhanced by 9.4%, 45.9%, and 466.8%, respectively. Moreover, SQ-2–biochar was demonstrated to have a notable capacity for removing Pb²⁺ and Al³⁺. The mineralization of Pb²⁺ and Al³⁺ was achieved through the use of SQ-2–biochar, as revealed by SEM-EDS, XRD, XPS, and FT-IR analyses, with the main precipitates being Pb₃(PO₄)₂ and AlPO₄. Functional groups such as C-O-C, C=O, N-H, P-O, and -O-H on the microbial surface were found to be involved in the biosorption process of Pb²⁺ and Al³⁺. In summary, SQ-2–biochar can effectively mineralize Pb²⁺ and Al³⁺, enhance the physiological properties of rice, and improve soil nutrients, thereby augmenting the antioxidant capacity, photosynthesis, and stress resistance of rice and ultimately promoting rice growth.