Polycyclic aromatic hydrocarbons (PAHs) are environmentally persistent pollutants that pose threats to both the environment and human health. Recently, bioremediation has emerged as a promising strategy for PAH pollution. NADH plays a crucial role in microbial metabolism and participates in PAH degradation. However, the mechanism underlying the influence of NADH on polycyclic aromatic hydrocarbon degradation remains unclear. The bacterium Novosphingobium pentaromativorans US6-1 degrades PAHs efficiently, and exogenous NADH supplementation promoted both cell growth and phenanthrene degradation. Promoter activity assays revealed that NADH upregulates the expression of PAH-degrading enzyme genes salA and xylE and enhanced the in vivo activity of the XylE enzyme. Since NADH did not act as a direct cofactor of XylE in cell-free assays, this enhancement is likely attributed to transcription upregulation and optimized intracellular conditions. Furthermore, NADH reduced intracellular reactive oxygen species (ROS) levels more effectively than antioxidant glutathione (GSH), suggesting that NADH supports cell fitness through mechanisms that extend beyond simple chemical ROS scavenging. Interestingly, NADH boosted the intracellular electron flux, and enhancing the electron transport system through either gene overexpression or FAD supplementation similarly improved PAH degradation. In conclusion, NADH promotes PAH degradation in N. pentaromativorans US6-1 through a multifaceted mechanism involving upregulating the key catabolic genes, enhancing in vivo critical enzyme activity, reducing intracellular ROS accumulation, and increasing electron flux. Our findings elucidate novel regulatory pathways of NADH in PAH degradation, thus highlighting its potential as a target for optimizing PAH bioremediation strategies.IMPORTANCEThe oxidation of polycyclic aromatic hydrocarbons (PAHs) by degrading bacteria generates toxic intermediates. Accumulation of these compounds disrupts intracellular redox balance, exacerbating cellular toxicity. Furthermore, microbial PAH degradation imposes high energy demands and depletes essential redox cofactors. Despite the critical role of NADH as a central energy currency and reductant in cellular metabolism, the specific mechanisms underlying the influence of NADH on PAH biodegradation, particularly its interplay with redox homeostasis, remain poorly understood. This study has elucidated that NADH enhances PAH degradation efficiency by alleviating oxidative stress due to PAH oxidation. This study provides insights critical for advancing engineered bioremediation solutions.

The transcriptional repressor PheR regulates uptake and catabolism of phenanthrene in Sphingobium sp. SHPJ-2

The persistence and hazardous potential of polycyclic aromatic hydrocarbons (PAHs), with compounds such as anthracene and phenanthrene, raise significant concerns about human health and environmental safety. PAHs are ubiquitous environmental pollutants originating from natural processes and anthropogenic activities, notably fossil fuel combustion. Due to their stability, they tend to accumulate in ecosystems, posing risks to wildlife and human health through bioaccumulation and potential carcinogenicity. Conventional remediation techniques, such as physical adsorption and biological treatment, often fall short in their efficiency and long-term sustainability. Thus, there is an urgent need for innovative methods that can effectively degrade these persistent organic pollutants. Here, we reviewed recent advancements in the photocatalytic degradation of anthracene and phenanthrene, with a focus on metal oxide-based nanocomposites. The major points were: (1) Metal oxides such as TiO2, ZnO, and CuO, recognized for their photocatalytic properties (they show significantly enhanced efficiency when utilized as a part of nanocomposites, primarily due to the improved charge separation, increased surface area, and numerous active sites); (2) The review of the photocatalytic mechanisms involved in PAH degradation, particularly through the generation of reactive oxygen species that can break down anthracene and phenanthrene into less harmful compounds; and (3) The insights into the formed intermediates and reaction pathways, which can help to deepen the understanding of PAH breakdown and support the design of more efficient catalytic systems for future environmental remediation applications.

Phenanthrene Degradation by <i>Bacillus cereus</i> Strain S2 Isolated from an Oil-Contaminated Mangrove Forest

Polycyclic aromatic hydrocarbons (PAHs) are widespread pollutants and especially difficult to degrade under anoxic conditions. The non-substituted three-ring PAH phenanthrene is activated through carboxylation to 2-phenanthroic acid which is then ligated to Co-enzyme A to produce 2-phenanthroyl-CoA, followed by step-wise reduction of the aromatic rings. The first reduction reaction is catalyzed by 2-phenanthroyl-CoA reductase producing dihydro-2-phenanthroyl-CoA. In this study, we elucidated the second reductase enzyme in the pathway, catalyzing the reduction of dihydro-2-phenanthroyl-CoA to hexahydro-2-phenanthroyl-CoA. Dihydro-2-phenanthroyl-CoA reductase (AprC) was heterologously overproduced in Escherichia coli and purified and characterized. AprC has a specific activity of 15.8 ± 0.3 nmol min-1 mg-1 and an apparent Km value of 59.9 ± 3.8 nM at pH 7.5. Dithionite-reduced methyl viologen is the preferred in vitro electron donor for the four electron-reduction reaction, but it also functions with NADH but not with NADPH. The intermediate appearance of tetrahydro-2-phenanthroyl-CoA during the reduction to hexahydro-2-phenanthroyl-CoA indicates that AprC catalyzes two consecutive two-electron reduction steps. AprC is a monomeric enzyme with a molecular mass of ≈73 kDa and contains one FMN, one FAD, and one 4Fe-4S cluster, indicating that the reductase belongs to the type III aryl-CoA reductases of the old-yellow enzyme family. The high amino acid sequence similarity between dihydro-2-phenanthroyl-CoA reductase and 2-naphthoyl-CoA reductase, as well as the similar cofactor coordination in both enzymes, suggested that dihydro-2-phenanthroyl-CoA reductase follows the same biochemical principle as naphthalene ring reduction by 2-naphthoyl-CoA reductase. Quantum chemical calculation indicated that 5,6,7,8,9,10-hexahydro-2-phenanthroyl-CoA (isomer 6a) is the most stable product of AprC out of eight possible isomers, although the real isomer is not known. The reductase also performed a two-electron reduction of chemically synthesized 9,10-dihydro-2-phenanthroyl-CoA to tetrahydro-2-phenanthroyl-CoA but at much lower reaction rates indicating that the 9,10-dihydro-2-phenanthroyl-CoA isomer is not the natural substrate of the enzyme and, thus, also not the real product of 2-phenanthroyl-CoA reduction by 2-phenanthroyl-CoA reductase AprB. Since 9,10-dihydro-2-phenanthroyl-CoA has two non-conjugated benzene rings, this also indicates that, surprisingly, type III aryl-CoA reductases can reduce benzene ring structures without additional ATP requirement.IMPORTANCEPolycyclic aromatic hydrocarbons (PAHs) are highly toxic, persistent pollutants found in the environment. The anaerobic degradation of larger three-ring PAHs like phenanthrene is still poorly understood. Here, we show that after activation to a CoA-ester, the resonance energy of the aromatic ring system of phenanthrene is overcome by consecutive two-electron reduction steps catalyzed by ATP-independent type III aryl-CoA reductases belonging to the old-yellow enzyme family. This finding contributes to our understanding of the anaerobic degradation of PAHs with three or more rings.

Phenanthrene (Phe) and fluoranthene (Fla) are polycyclic aromatic hydrocarbons (PAHs) known for their significant toxicity and resistance to degradation, making them biohazardous substances. This study explains the efficient degradation of Phe and Fla using two bacterial isolates-Pseudomonas aeruginosa BB-BE3, and P. aeruginosa BBBJ. These isolates produced excellent amount of rhamnolipid-like glycolipid biosurfactant, with strong emulsification activity. The isolate BB-BE3 attained degradation rates of up to 93% for Phe and 73% for Fla, while BBBJ achieved degradation rate of 81% for Phe and 76% for Fla, respectively under in vitro conditions. Both isolates were found to produce catechol 1,2 dioxygenase and catechol 2,3 dioxygenase enzymes. In microcosm study, treatment of PAH-contaminated soil with biosurfactant-producing bacterial isolates in combination with their extracted biosurfactants resulted in substantially enhanced degradation efficiencies, achieving 89-99% PAHs removal across all experimental setups compared to the control. Soil enzyme activities, including dehydrogenase and fluorescein diacetate hydrolysis, were evaluated as indicators of microbial metabolic activity. Notably, soils inoculated with biosurfactant-producing bacteria along with extracted biosurfactants exhibited elevated enzyme activities at both 15 and 30days of incubation, reflecting sustained and robust microbial activity. Collectively, these findings demonstrate the strong potential of biosurfactant-producing bacterial isolates as an effective bioremediation strategy for the degradation of PAHs in contaminated soils.

Efficient activation of persulfate by iron nanoparticles supported on nitrogen-doped beet biochar for phenanthrene degradation: Synthesis, performance, synergistic mechanisms, and applications

Evidence for priming-enhanced microbial degradation of polycyclic aromatic hydrocarbons in marine sediments.

Synergistic division of labor in a bacterial consortium for enhanced phenanthrene mineralization under cadmium stress: mechanisms of degradation-detoxification coordination.

Polycyclic aromatic hydrocarbons (PAHs) pose a persistent threat to soil ecosystems due to their recalcitrant nature and widespread distribution. This study investigates the role of humic acids (HAs) in enhancing phenanthrene (PHE) degradation and electron transfer efficiency in soil bioelectrochemical systems (SBSs). A series of HAs-amended SBSs was constructed and systematically evaluated for electrochemical performance, PHE removal efficiency, and HA component evolution. Fluorescence excitation-emission matrix spectroscopy coupled with parallel factor analysis, Fourier transform infrared spectroscopy, two-dimensional correlation spectroscopy, and structural equation modeling were employed to reveal the redox transformation pathways of HAs and their interactions with microbial communities. The results revealed that Components C1 and C3 of HAs played distinct yet complementary roles in facilitating extracellular electron transfer (EET). C1, with its low molecular weight and high mobility, served as a diffusible electron shuttle promoting long-distance electron transport. C3, enriched with quinonoid moieties and a stable aromatic backbone, supported sustained redox cycling and long-term system stability. Although Component C2 did not directly contribute to EET, it underwent microbial- and electrochemically driven transformation into C1 and C3, reinforcing the formation of a robust electron transfer network. These findings highlight the functional differentiation and synergistic interactions between HA subcomponents in promoting PHE degradation. From an environmental perspective, this study offers a novel and practical strategy for enhancing in situ bioremediation of PAH-contaminated soils. The utilization of natural HAs as electron mediators not only improves remediation efficiency but also aligns with sustainable and eco-friendly treatment principles, providing theoretical support for the development of advanced soil bioelectrochemical remediation technologies.

Cd distribution and phenanthrene degradation pathways in Cd-tolerant and phenanthrene-degrading bacteria under elevated Cd concentrations: A low-toxicity convergence strategy.

Birnessite-assisted ecological adaptation of Sphingomonas HDJX-2 accelerates phenanthrene degradation in contaminated soils

Deciphering the divergent roles of glycoside surfactants in alkali-activated persulfate remediation of phenanthrene: Mechanistic and practical implications.

In this study, the gradient pressure enrichment method was first used to screen out an environmental bacterium with the degradation ability of typical petroleum hydrocarbons such as phenanthrene and n-hexadecane, identified as Pseudomonas and named TB-1, from soil samples collected from 9 crude oil-contaminated sites; then, enhanced degradation of mixed organic pollutants, including petroleum and chlorinated hydrocarbons which are commonly coexistent, was achieved by a dual-bacteria system, with the addition of a laboratory storage strain Pseudomonas BL5. The degradation rate of phenanthrene and n-hexadecane by the dual-bacteria system was lower compared with the single bacterium Pseudomonas TB-1 under the tested conditions: phenanthrene degradation decreased from 44.2% to 23.1%, and n-hexadecane degradation decreased from 77.9% to 54.7% at a pollutant concentration of 100 mg/L after 7 days of cultivation. In contrast, the degradation ability of the dual-bacteria system against the mixed pollutants composed of petroleum and chlorinated hydrocarbons was good, with a degradation rate of 82.2% for phenanthrene, 89.2% for n-hexadecane, 73.1% for p-chlorobenzene, and 95.7% for dichloroethane with each concentration of 100 mg/L after 7 days. These results indicate that, although the dual-bacteria system does not enhance degradation under single-hydrocarbon conditions, its performance under chemically complex co-contamination suggests a potential cooperative or complementary interaction between the two strains. Such interactions are proposed here as a working hypothesis rather than a confirmed mechanism. Overall, the defined dual-Pseudomonas system shows promising potential for the treatment of environments co-contaminated with petroleum and chlorinated hydrocarbons.

Phenanthrene-Induced Proteomic Adaptations in Marine Pseudomonas oleovorans: Insights into PAH Biodegradation Mechanisms

Integrated multi-omics analysis reveals the mechanism of birnessite-enhanced phenanthrene degradation by Novosphingobium sp. HDJX-2 bacteria

Polycyclic aromatic hydrocarbons (PAH) are prevalent environmental contaminants, which exhibit the mutagenic, carcinogenic, and teratogenic properties. The growing demand for efficient PAH biodegradation (BD), particularly in wastewater treatment. This research investigates hydrocarbon degradation using Vreelandella piezotolerant DM1 across a various pH levels (4, 6, 7, 8, and 10) and its enzymatic capabilities. The study assessed the degradation potential of anthracene and phenanthrene under varying PAH concentrations and pH conditions. Optimal bacterial growth and degradation were observed at 300mg/L of both anthracene and phenanthrene at pH 8. To elucidate the degradation mechanisms, crucial intermediates were identified using gas chromatography mass-spectrometry (GC-MS). The hydrocarbon breakdown intermediates including anthracene-cis-1,2-dihydrodiol, (3Z)-4-[3-hydroxy(2-naphthyl)]-2-oxobut-3-enoic acid, 6,7-benzocoumarin, 1-hydroxy-2-naphthaldehyde, phenanthrene-cis-1,2-dihydrodiol, 1-hydroxy-2-naphthoic acid, and salicylic acid were observed during BD. Both intermediate compounds were conformed the salicylic acid pathway. GC-MS confirms the efficient degradation rates of 62% for anthracene, 82% for phenanthrene, and 83% for mixed hydrocarbons. These observations confirm that optimal conditions are obligatory for the enzymatic activity of the DM1 and a biodegradation pathway was proposed on the identified intermediates. In conculsion, V. piezotolerant DM1 serves as a potential candidate for hydrocarbon degradation in contaminated environment.

Enhanced catalytic efficiency of CeO2/BC@Fe3O4 magnetic catalyst in activating peroxymonosulfate for effective degradation of polycyclic aromatic hydrocarbons in water.

pH-dependent phenanthrene degradation by Fe(III)-sodium tripolyphosphate-activated H2O2: dominant reactive oxygen species and roles of ligands

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.