Determining the degradation mechanism and application potential of benzopyrene-degrading bacterium Acinetobacter XS-4 by screening

Enhanced biodegradation of benzo[a]pyrene with Trametes versicolor stimulated by citric acid

Polycyclic aromatic hydrocarbons (PAHs) are a class of persistent organic pollutants with carcinogenic, mutagenic and teratogenic effects. The white-rot fungi in the fungal group have significant degradation ability for high molecular weight organic pollutants. However, exogenous fungi are easily antagonized by indigenous microorganisms. Low molecular weight organic acids, a small molecular organic matter secreted by plants, can provide carbon sources for soil microorganisms. Combining organic acids with white rot fungi may improve the nutritional environment of fungi. In this study, immobilized Trametes versicolor was used to degrade benzo[a]pyrene in soil, and its effect on removing benzo[a]pyrene in soil mediated by different low molecular weight organic acids was investigated. The results showed that when the degradation was 35 days, the removal effect of the experimental group with citric acid was the best, reaching 43.7%. The degradation effect of Trametes versicolor on benzo[a]pyrene was further investigated in the liquid medium when citric acid was added, and the effects of citric acid on the biomass, extracellular protein concentration and laccase activity of Trametes versicolor were investigated by controlling different concentrations of citric acid. In general, citric acid can act as a carbon source for Trametes versicolor and promote its extracellular protein secretion and laccase activity, thereby accelerating the mineralization of benzo[a]pyrene by Trametes versicolor. Therefore, citric acid can be used as a biostimulant in the remediation of PAHs contaminated soil with Trametes versicolor.

Fulvic acid enhancing pyrene biodegradation by immobilized Stenotrophomonas maltophilia: Effect and mechanism

Immobilization technology is a promising way to improve effectiveness and stability of microbial remediation for polycyclic aromatic hydrocarbons (PAHs), in which carrier material is one of key factors restricting removal efficiency. In this study, fulvic acid-wheat straw biochar (FA/WS) composites were applied for immobilization of an efficient PAHs degrading bacterium Stenotrophomonas maltophilia (SPM). FA/WS&SPM showed superior degradation capacity than free bacteria and biochar-immobilized bacteria, with the removal efficiency of pyrene (20 mg L-1) reaching 90.5 % (7 days). Transcriptome analysis revealed that FA in the carrier materials can promote transportation and degradation of pyrene, and cell growth, as well as inhibit cell apoptosis. Enzyme activity and degradation products detection showed that SPM utilized both phthalic acid and salicylic acid metabolic pathways to degrade pyrene. Practicality of FA/WS&SPM for different kinds of PAHs remediation had been verified in contaminated soil, demonstrating a great potential in the field of PAHs polluted sites remediation.

A systematic review of polycyclic aromatic hydrocarbon pollution: A combined bibliometric and mechanistic analysis of research trend toward an environmentally friendly solution

Pollution caused by polycyclic aromatic hydrocarbons (PAHs) is a significant concern. This concern has become more problematic given the rapid modification of PAHs in the environment during co-contamination to form substituted PAHs. This review aims to integrate bibliometric analysis with a rigorous study of mechanistic insights, resulting in a more comprehensive knowledge of evolving research trends on PAH remediation. The results show that research in this field has progressed over the years and peaked in 2022, potentially due to the redirection of resources toward emerging pollutants, hinting at the dynamic nature of environmental research priorities. During this year, 158,147 documents were published, representing 7 % of the total publications in the field between 2000 and 2023. The different remediation methods used for PAH remediation were identified and compared. Bioremediation, having >90 % removal efficiency, has been revealed to be the best technique because it is cost-effective and easy to operate at large scale in situ and ex-situ. The current challenges in PAH remediation have been detailed and discussed. Implementing innovative and sustainable technologies that target pollutant removal and valuable compound recovery is necessary to build a more robust future for water management.

Biodegradation of penicillin G sodium by Sphingobacterium sp. SQW1: Performance, degradation mechanism, and key enzymes

Biodegradation is an efficient and cost-effective approach to remove residual penicillin G sodium (PGNa) from the environment. In this study, the effective PGNa-degrading strain SQW1 (Sphingobacterium sp.) was screened from contaminated soil using enrichment technique. The effects of critical operational parameters on PGNa degradation by strain SQW1 were systematically investigated, and these parameters were optimized by response surface methodology to maximize PGNa degradation. Comparative experiments found the extracellular enzyme to completely degrade PGNa within 60 min. Combined with whole genome sequencing of strain SQW1 and LC-MS analysis of degradation products, penicillin acylase and β-lactamase were identified as critical enzymes for PGNa biodegradation. Moreover, three degradation pathways were postulated, including β-lactam hydrolysis, penicillin acylase hydrolysis, decarboxylation, desulfurization, demethylation, oxidative dehydrogenation, hydroxyl reduction, and demethylation reactions. The toxicity of PGNa biodegradation intermediates was assessed using paper diffusion method, ECOSAR, and TEST software, which showed that the biodegradation products had low toxicity. This study is the first to describe PGNa-degrading bacteria and detailed degradation mechanisms, which will provide new insights into the PGNa biodegradation.

Isolation, identification, degradation mechanism and exploration of active enzymes in the ochratoxin A degrading strain Acinetobacter pittii AP19

Ochratoxin A (OTA) is a polyketide mycotoxin that commonly contaminates agricultural products and causes significant economic losses. In this study, the efficient OTA-degrading strain AP19 was isolated from vineyard soil and was identified as Acinetobacter pittii. Compared with growth in nutrient broth supplemented with OTA (OTA-NB), strain AP19 grew faster in nutrient broth (NB), but the ability of the resulting cell lysates to remove OTA was weaker. After cultivation in NB, the cell lysate of strain AP19 was able to remove 100% of 1 mg/L OTA within 18 h. The cell lysate fraction > 30 kDa degraded 100% of OTA within 12 h, while the fractions < 30 kDa were practically unable to degrade OTA. Further anion exchange chromatography of the > 30 kDa fraction yielded two peaks exhibiting significant OTA degradation activity. The degradation product was identified as OTα. Amino acid metabolism exhibited major transcriptional trends in the response of AP19 to OTA. The dacC gene encoding carboxypeptidase was identified as one of the contributors to OTA degradation. Soil samples inoculated with strain AP19 showed significant OTA degradation. These results provide significant insights into the discovery of novel functions in A. pittii, as well as its potential as an OTA decomposer.

Molecular and metabolic characterization of petroleum hydrocarbons degrading Bacillus cereus

Hydrocarbon constituents of petroleum are persistent, bioaccumulated, and bio-magnified in living tissues, transported to longer distances, and exert hazardous effects on human health and the ecosystem. Bioaugmentation with microorganisms like bacteria is an emerging approach that can mitigate the toxins from environmental sources. The present study was initiated to target the petroleum-contaminated soil of gasoline stations situated in Lahore. Petroleum degrading bacteria were isolated by serial dilution method followed by growth analysis, biochemical and molecular characterization, removal efficiency estimation, metabolites extraction, and GC-MS of the metabolites. Molecular analysis identified the bacterium as Bacillus cereus, which exhibited maximum growth at 72 hours and removed 75% petroleum. Biochemical characterization via the Remel RapID™ ONE panel system showed positive results for arginine dehydrolase (ADH), ornithine decarboxylase (ODC), lysine decarboxylase (LDC), o-nitrophenyl-β-D-galactosidase (ONPG), p-nitrophenyl-β-D-glucosidase (βGLU), p-nitrophenyl-N-acetyl-β-D-glucosaminidase (NAG), malonate (MAL), adonitol fermentation (ADON), and tryptophane utilization (IND). GC-MS-based metabolic profiling identified alcohols (methyl alcohol, o-, p- and m-cresols, catechol, and 3-methyl catechol), aldehydes (methanone, acetaldehyde, and m-tolualdehyde), carboxylic acid (methanoic acid, cis,cis-muconic acid, cyclohexane carboxylic acid and benzoic acid), conjugate bases of carboxylic acids (benzoate, cis,cis-muconate, 4-hydroxybenzoate, and pyruvate) and cycloalkane (cyclohexene). It suggested the presence of methane, methylcyclohexane, toluene, xylene, and benzene degradation pathways in B. cereus.

Biodegradation of benzo[a]pyrene by a marine Chlorella vulgaris LH-1 with heterotrophic ability

In this study, a microalga, Chlorella vulgaris LH-1, with heterotrophic ability to degrade BaP was explored. The effect of BaP concentration on microalga growth was investigated, and the possible biodegradation mechanism of BaP was proposed. Results showed that low BaP concentration (<5 mg/L) had less negative influence on the growth of this microalga under mixotrophic condition, but high BaP concentration (>5 mg/L) had a significant inhibitory effect on its growth. During heterotrophic cultivation, low BaP concentration (<20 mg/L) promoted the growth of C. vulgaris LH-1, whereas high BaP concentration (>20 mg/L) inhibited its growth significantly. The degradation rates of mixotrophic and heterotrophic C. vulgaris LH-1 were 62.56 %-74.13 % and 52.07 %-71.67 %, respectively, when the BaP concentration ranged from 0.5 mg/L to 2 mg/L. The expression of functional enzyme genes of C. vulgaris LH-1 such as phenol 2-monooxygenase activity, protocatechuate 3,4-dioxygenase activity, catechol 1,2-dioxygenase activity, styrene degradation, and benzoate degradation were upregulated in the process of BaP degradation. C. vulgaris LH-1 may degrade BaP by monooxygenase and dioxygenase simultaneously. The degradation of BaP by this microalga under mixotrophic condition goes through the degradation pathway of phthalic acid, whereas it goes through the degradation pathway of benzoic acid under heterotrophic condition.