Individual or synchronous biodegradation of di-n-butyl phthalate and phenol by Rhodococcus ruber strain DP-2

Mechanistic insight into degradation of dibutyl phthalate by microorganism in sediment-water environment: Metabolic pathway, community succession, keystone phylotypes and functional genes

Despite extensive studies on dibutyl phthalate (DBP) degradation in isolated bacterial cultures, the primary degraders, community dynamics, and metabolic pathways involved in its biotransformation within complex sediment microbial communities remain poorly understood. In this study, we aimed to investigate the biotransformation mechanism of DBP by microorganisms in a sediment-water system by employing gas chromatography-mass spectrometry, 16S rRNA gene sequencing, metagenomic analysis, and bacterial isolation techniques. We observed that DBP biotransformation has three distinct phases: lag, degradative, and stationary. During the degradative phase, DBP gets progressively degraded by microorganisms, resulting in a microbial community with reduced stability and ambiguous boundaries. DBP, primarily metabolised by key phylotypes into monobutyl phthalate (MBP), phthalic acid (PA), and protocatechuic acid, subsequently enters the tricarboxylic acid (TCA) cycle. Through metagenomic analysis, ten functional genes from five genera were identified as crucial for DBP metabolism. Firstly, Arthrobacter degrades DBP into MBP and PA using pheA. Subsequently, Acinetobacter, Massilia, and Arthrobacter convert PA into TCA cycle intermediates using phtBAaAbAcAd and pcaCH. Concurrently, Hydrogenophaga and Acidovorax degrade PA to TCA cycle intermediates through pht1234 and ligAB. Genes related to amino acid synthesis, ABC transporters, and two-component regulatory systems also contribute significantly. Thus, the listed key bacteria, along with their diverse functional genes, collectively exhibit a high capacity for DBP degradation. This study provides insights into the bacterial responses to DBP degradation and offers a theoretical basis for the prevention and control of this pollutant.

Risk assessment of China's Eastern Route of the South-to-north Water Diversion Project from the perspective of Phthalate Esters occurrence in the impounded lakes

Phthalate esters (PAEs) are widely utilized and can accumulate in lacustrine ecosystems, posing significant ecological and human health hazards. Most studies on PAEs focus on individual lakes, lacking a comprehensive and systematic perspective. In response, we have focused our investigation on characteristic lakes situated along the Eastern Route of the South-to-north Water Diversion Project (SNWDP-ER) in China. We have detected 16 PAE compounds in the impounded lakes of the SNWDP-ER by collecting surface water samples using solid-phase extraction followed by gas chromatography analysis. The concentration of PAEs were found to between 0.80 to 12.92 μg L-1. Among them, Bis (2-ethylhexyl) phthalate (DEHP) was the most prevalent, with mean concentration of 1.56 ± 0.62 μg L-1 (48.44%), followed by Diisobutyl phthalate (DIBP), 0.64 ± 1.40 μg L-1 (19.87%). Spatial distribution showed an increasing trend in the direction of water flow. Retention of DEHP and DIBP has led to increased environmental risks. DEHP, Dimethyl phthalate (DMP) etc. determined by agriculture and human activities. Additionally, Dibutyl phthalate (DBP) and DIBP mainly related to the use of agricultural products. To mitigate the PAEs risk, focusing on integrated management of the lakes, along with the implementation of stringent regulations to control the use of plasticizes in products.

Adaptive changes of swimming crab (Portunus trituberculatus) associated bacteria helping host against dibutyl phthalate toxification

The pollution of dibutyl phthalate (DBP) in aquatic environments is becoming an extensive environmental problem and detrimental to aquatic animals. Here, we quantified the response pattern of the bacterial community and metabolites of swimming crab (Portunus trituberculatus) juveniles exposed to 0.2, 2, and 10 mg/L DBP using 16 S rRNA gene amplicon sequencing coupled with metabolomic technique. The results showed that DBP changed the bacterial community compositions in a concentration-dependent pattern and decreased the Shannon index at the second developmental stage of the swimming crabs. The Rhodobacteraceae taxa were specifically enriched by crabs when challenged by 2 and 10 mg/L DBP, with an increased in Shannon index and enhanced drift in its assembly. Moreover, DBP changed the metabolic profiling of the swimming crab, highlighted by increased levels of lactate, valine, methionine, lysine, and phenylalanine in the 10 mg/L DBP-exposed crabs. Rhodobacteraceae presented the most considerable contribution to the metabolic potentials in phthalate and benzoate degradation, lactate production, and amino acid biosynthesis. Overall, our results indicated an adaptive change of crab-associated bacteria helped the host resist DBP stress. The findings extend our insights into the relationship between the microbiota and its host metabolism under DBP stress and reveal the potential microbiota modalities for DBP detoxification.

Rhodococcus Strains from the Specialized Collection of Alkanotrophs for Biodegradation of Aromatic Compounds

The ability to degrade aromatic hydrocarbons, including (i) benzene, toluene, o-xylene, naphthalene, anthracene, phenanthrene, benzo[a]anthracene, and benzo[a]pyrene; (ii) polar substituted derivatives of benzene, including phenol and aniline; (iii) N-heterocyclic compounds, including pyridine; 2-, 3-, and 4-picolines; 2- and 6-lutidine; 2- and 4-hydroxypyridines; (iv) derivatives of aromatic acids, including coumarin, of 133 Rhodococcus strains from the Regional Specialized Collection of Alkanotrophic Microorganisms was demonstrated. The minimal inhibitory concentrations of these aromatic compounds for Rhodococcus varied in a wide range from 0.2 up to 50.0 mM. o-Xylene and polycyclic aromatic hydrocarbons (PAHs) were the less-toxic and preferred aromatic growth substrates. Rhodococcus bacteria introduced into the PAH-contaminated model soil resulted in a 43% removal of PAHs at an initial concentration 1 g/kg within 213 days, which was three times higher than that in the control soil. As a result of the analysis of biodegradation genes, metabolic pathways for aromatic hydrocarbons, phenol, and nitrogen-containing aromatic compounds in Rhodococcus, proceeding through the formation of catechol as a key metabolite with its following ortho-cleavage or via the hydrogenation of aromatic rings, were verified.

Biodegradation of dibutyl phthalate by a novel endophytic Bacillus subtilis strain HB-T2 under in-vitro and in-vivo conditions

The environmental prevalence and potential toxicity of dibutyl phthalate (DBP) motivate the attempt to develop feasible strategies to deal with DBP contamination. In this study, a strain of endphytic bacteria HB-T2 was isolated from sorrel roots and identified as Bacillus sp. by analysing its morphology, physiology, biochemistry and 16S rDNA sequence. The degradation efficiency of DBP by HB-T2 was almost identical under the temperature of 30∼40°C, but was significantly enhanced as the culture pH and inoculum size increases from 6.0 to 8.0, and 1% to 5% respectively. The degradation kinetics of DBP could be well described by the first-order kinetic model, with the degradation half-life ranging from 1.59 to 7.61 h when the initial concentrations of DBP were in the range of 5-20 mg/L. LC-MS analysis of the culture samples taken at varying intervals revealed monobutyl phthalate, phthalic acid and protocatechuic acid as the major metabolic intermediates during the degradation process. HB-T2 exhibited an excellent capability to degrade a wide range of phthalate esters (PAEs), especially butyl benzyl phthalate (BBP), dipentyl phthalate (DPP), and diisobutyl phthalate (DIBP). Inoculation of HB-T2 into Chinese cabbage (Brassica chinensis L.) growing in DBP-contaminated soils could significantly reduce the DBP levels in plant tissues and relieve the phytotoxic effects of DBP. Results of this study highlighted the great potential of this novel endophytic Bacillus subtilis strain HB-T2 for bioremediation of PAEs contamination and improvement of agricultural product safety by reducing PAEs accumulation in edible crops.

Phthalate Esters Metabolic Strain Gordonia sp. GZ-YC7, a Potential Soil Degrader for High Concentration Di-(2-ethylhexyl) Phthalate

As commonly used chemical plasticizers in plastic products, phthalate esters have become a serious ubiquitous environmental pollutant, such as in soil of plastic film mulch culture. Microbial degradation or transformation was regarded as a suitable strategy to solve the phthalate esters pollution. Thus, a new phthalate esters degrading strain Gordonia sp. GZ-YC7 was isolated in this study, which exhibited the highest di-(2-ethylhexyl) phthalate degradation efficiency under 1000 mg/L and the strongest tolerance to 4000 mg/L. The comparative genomic analysis results showed that there exist diverse esterases for various phthalate esters such as di-(2-ethylhexyl) phthalate and dibutyl phthalate in Gordonia sp. GZ-YC7. This genome characteristic possibly contributes to its broad substrate spectrum, high degrading efficiency, and high tolerance to phthalate esters. Gordonia sp. GZ-YC7 has potential for the bioremediation of phthalate esters in polluted soil environments.

Synchronous degradation of phenol and aniline by Rhodococcus sp.strain PB-1entrapped in sodium alginate-bamboo charcoal-chitosan beads

The biodegradation of benzene series compounds is a difficult problem in environment pollution control, which is attributed to the deficiency of high efficiency bacteria and suitable embedding materials. In this study, the immobilized cells Rhodococcussp. strain PB-1 was used to synchronously biodegrade phenol and aniline by entrapped in sodium alginate (SA)-bamboo charcoal (BC)-chitosan acetate (CA) beads. The free cells of the strain PB-1 could completely degrade 1500 mg/L phenol or 800 mg/L aniline within 48 h, while the degradation rate of 2000 mg/L phenol and 1500 mg/L aniline was 35.76% and 68.06% at 72 h, respectively. The ortho-cleavage pathway was used to degrade phenol and aniline by strain PB-1. However, after entrapped with SA-BC-CA beads,the removal rate of 2000 mg/L phenol was 100% at 108 h, 1500 mg/L aniline was 100% at 62 h and 2000-3000 mg/L total toxic compounds was over 95% at 120 h. These beads could be used four times and were more effective than SA or SA-BC beads. The SA-BC-CA beads could remarkably improve the stability and degradation efficiency of strain PB-1, and thus provide a potential application in the removal of phenol and aniline in wastewater.

Overexpression of Capsular Polysaccharide Biosynthesis Protein in Lactobacillus plantarum P1 to Enhance Capsular Polysaccharide Production for Di-n-butyl Phthalate Adsorption

Exopolysaccharides (EPSs) such as capsular polysaccharide (CPS) are important bioactive carbohydrate compounds and are often used as bioenrichment agents and bioabsorbers to remove environmental pollutants like di-n-butyl phthalate (DBP). Among the EPS-producing bacteria, lactic acid bacteria (LAB) have gained the most attention. As generally recognized as safe (GRAS) microorganisms, LAB can produce EPSs having many different structures and no health risks. However, EPS production by LAB does not meet the needs of large-scale application on an industrial scale. Here, the capA gene (encoding CPS biosynthesis protein) was overexpressed in Lactobacillus plantarum P1 to improve the production of EPSs and further enhance the DBP adsorption capability. Compared with P1, the CPS production in capA overexpressed strain was increased by 11.3 mg/l, and the EPS thickness was increased from 0.0786 ± 0.0224 μm in P1 to 0.1160 ± 0.0480 μm in P1-capA. These increases caused the DBP adsorption ratio of P1-capA to be doubled. Overall, the findings in this study provide a safe method for the adsorption and removal of DBP.

High-efficiency degradation of phthalic acid esters (PAEs) by Pseudarthrobacter defluvii E5: Performance, degradative pathway, and key genes

Phthalic acid esters (PAEs) are a class of biologically accumulated carcinogenic and teratogenic toxic chemicals that exist widely in the environment. This study, Pseudarthrobacter defluvii E5 was isolated from agricultural soils and showed efficient PAEs-degradation and -mineralization abilities for five PAEs, and encouraging PAEs tolerance and bioavailable range for dibutyl phthalate (DBP) and bis(2-ethylhexyl) phthalate (DEHP) (0.25-1200 mg/L). The complete catalytic system in E5 genome enables PAEs to be degraded into monoester, phthalate (PA) and Protocatechuic acid (PCA), which eventually enter the tricarboxylic acid cycle (TCA cycle). The preferred PAEs-metabolic pathway in soil by E5 is the metabolism induced by enzymes encoded by pehA, mehpH, pht Operon and pca Operon. For the first time, two para-homologous pht gene clusters were found to coexist on the plasmid and contribute to PAEs degradation. Further study showed that P. defluvii E5 has a broad application prospect in microplastics-contaminated environments.

The conversion of the nutrient condition alter the phenol degradation pathway by Rhodococcus biphenylivorans B403: A comparative transcriptomic and proteomic approach

Highly toxic phenol causes a threat to the ecosystem and human body. The development of bioremediation is a crucial issue in environmental protection. Herein, Rhodococcus biphenylivorans B403, which was isolated from the activated sludge of the sewage treatment plant, exhibited a good tolerance and removal efficiency to phenol. The degradation efficiency of phenol increased up to 62.27% in the oligotrophic inorganic medium (MM) containing 500-mg/L phenol at 18 h. R. biphenylivorans B403 cultured in the MM medium showed a higher phenol degradation efficiency than that in the eutrophic LB medium. On the basis of the transcriptomic and proteomic analysis, a total of 799 genes and 123 proteins showed significantly differential expression between two different culture conditions, especially involved in phenol degradation, carbon metabolism, and nitrogen metabolism. R. biphenylivorans B403 could alter the phenol degradation pathway by facing different culture conditions. During the phenol removal in the oligotrophic inorganic medium, muconate cycloisomerase, acetyl-CoA acyltransferase, and catechol 1,2-dioxygenase in the ortho-pathway for phenol degradation showed upregulation compared with those in the eutrophic organic medium. Our study provides novel insights into the possible pathway underlying the response of bacterium to environmental stress for phenol degradation.

Acinetobacter tandoii ZM06 Assists Glutamicibacter nicotianae ZM05 in Resisting Cadmium Pressure to Preserve Dipropyl Phthalate Biodegradation

Dipropyl phthalate (DPrP) coexists with cadmium as cocontaminants in environmental media. A coculture system including the DPrP-degrading bacterium Glutamicibacter nicotianae ZM05 and the nondegrading bacterium Acinetobacter tandoii ZM06 was artificially established to degrade DPrP under Cd(II) stress. Strain ZM06 relieved the pressure of cadmium on strain ZM05 and accelerated DPrP degradation in the following three ways: first, strain ZM06 adsorbed Cd(II) on the cell surface (as observed by scanning electron microscopy) to decrease the concentration of Cd(II) in the coculture system; second, the downstream metabolites of ZM05 were utilized by strain ZM06 to reduce metabolite inhibition; and third, strain ZM06 supplied amino acids and fatty acids to strain ZM05 to relieve stress during DPrP degradation, which was demonstrated by comparative transcriptomic analysis. This study provides an elementary understanding of how microbial consortia improve the degradation efficiency of organic pollutants under heavy metals contamination.

Network-directed isolation of the cooperator Pseudomonas aeruginosa ZM03 enhanced the dibutyl phthalate degradation capacity of Arthrobacter nicotianae ZM05 under pH stress

Dibutyl phthalate (DBP), widely used as plasticizer, is a typical soil contaminant. A new isolate, Arthrobacter nicotianae ZM05, is efficient at degrading DBP but lacks stress resistance to adverse environments. In this study, to isolate effective cooperators of strain ZM05 under pH stress and explore the effects of DBP on the bacterial community structure and interaction between bacteria, a microcosm experiment was conducted by supplying the exogenous DBP-degrading bacteria ZM05. 16S rRNA gene sequencing analysis showed that DBP contamination decreased microbial community diversity and weakened potential interactions between microorganisms, evidenced by fewer links, lower average degree, and lower average clustering coefficients in the cooccurrence network. Furthermore, the subnetworks showed that DBP shifted the interactions between strain ZM05 and other microbes. Based on the prediction of the network, the nondegrading bacterium Pseudomonas aeruginosa ZM03 was isolated and proven through coculture experiments to have a positive interaction with strain ZM05 during DBP degradation under pH stress. Strain ZM03 could utilize downstream acidic metabolites to alleviate acid inhibition and accelerate degradation. This study provides solid evidence that bacterial communities adjust their interactions to adapt to DBP stress and provides new insight into the prediction of microbes that are cooperative with degrading bacteria.

Remediation strategies for mitigation of phthalate pollution: Challenges and future perspectives

Phthalates are a group of emerging xenobiotic compounds commonly used as plasticizers. In recent times, there has been an increasing concern over the risk of phthalate exposure leading to adverse effects to human health and the environment. Therefore, it is necessary to not only understand the current status of phthalate pollution, their sources, exposure routes and health impacts, but also identify remediation technologies for mitigating phthalate pollution. Present review article aims to inform its readers about the ever increasing data on health burdens posed by phthalates and simultaneously highlights the recent advancements in research to alleviate phthalate contamination from environment. The article enumerates the major phthalates in use today, traces their environmental fate, addresses their growing health hazard concerns and largely focus on to provide an in-depth understanding of the different physical, chemical and biological treatment methods currently being used or under research for alleviating the risk of phthalate pollution, their challenges and the future research perspectives.

Biostimulation of Rhodovulum sp., for enhanced degradation of di-n-butyl phthalate under optimum conditions

Di-butyl phthalate (DBP) is an extensively applied synthetic plasticizer, toxic organic compound with elevated concentrations in aquatic and terrestrial ecosystem that cause serious risk to the human health. A marine bacterium Rhodovulum sp. DBP07 isolated from sea water with proficient of efficiently degrading DBP. The maximum DBP degradation (70.2%) and the cell growth (1.3 OD_600nm) were observed at 600 mg/L. The DBP degradation characteristics of the isolate Rhodovulum sp. DBP07 with diverse preliminary concentrations of DBP was found to be 200 ˃ 400 ˃ 600 ˂ 800 ˂ 1000 mg/L DBP. Glucose was identified as most favorable nutrient factor for the enhanced growth and showed 79.8 and 77.4% of degradation rate at 5.0 and 2.0 g/L respectively. The influence of the carbon sources on DBP degradation was found to be Glucose ˃ fructose ˃ sucrose ˃ maltose ˃ lactose ˃ citric acid ˃ starch. Box-Behnken (BBD) statistical optimization results showed enhanced DBP biodegradation rate (91.1%) at pH 7.0, 3% of NaCl concentration with 3 days of incubation. Two intermediate compounds were observed in the retention times of 10.8 and 12.2 which are identified as diethyl phthalate (DEP) and mono-nbutyl phthalate (MBP) using Gas chromatography mass spectroscopy (GC-MS). Furthermore, the phthalate (pht) gene expression pattern under DBP stress was analyzed using RT-qPCR and the maximum fold change (5.7 fold) was observed at 3 day of incubation. Overall, the observed results indicate the possibility of utilizing Rhodovulum sp. for remediation of DBP contaminated environment.

Biodegradability of di-(2-ethylhexyl) phthalate by a newly isolated bacterium Achromobacter sp. RX

Di-(2-ethylhexyl) phthalate (DEHP) is a chemical plasticizer that has been commonly used in the manufacture of polyvinyl chloride. DEHP is one of the environmental pollution sources. In this study, a gram-negative strain RX bacterium utilizing DEHP as sole carbon source was isolated from activated sludge through screening test. This strain RX was identified as Achromobacter sp. RX based on its morphology, physiological properties and 16S rRNA gene sequence analysis. The results showed that the optimal conditions for the DEHP degradation were 30.0 °C and pH 7.0. The DEHP degradation induced by strain RX demonstrated nitrogen source dependent, while followed a decreasing degradation rate under the source of: NO₃^- > NH₄⁺ > NO₂^-. The biodegradability of Achromobacter sp. RX was enhanced with Masson pine seed powder as a co-metabolic substrate and Tween-80 as a solubilizing agent. Meanwhile, the degrading kinetics analysis was performed in the condition of DEHP as sole carbon source. The DEHP degradation curves fitted well with the first-order kinetic model at 50-300 mg/L of DEHP, with the half-life ranging from 13.0 to 16.4 h. During the biodegradation of DEHP, mono-(2-ehtylhexyl) phthalate (MEHP) was firstly generated through de-esterification, followed by the formation of phthalic acid and benzoic acid after further de-esterification of MEHP. Benzoic acid was finally mineralized to CO₂ and H₂O. The decontamination of DEHP-contaminated soil by Achromobacter sp. RX was investigated using a rotating-drum bioreactor. Evolution of total organic carbon from the contaminated soil showed that 86.4%-91.7% of DEHP was mineralized at pH 7.0 and 30.0 °C within 96 h. Reusability of Achromobacter sp. RX and its lifetime were observed over six consecutive cycles. Thus, Achromobacter sp. RX possessed high DEHP biodegradability, which provided a good potential in dealing with DEHP-contaminated soil.

Biodegradation of Di (2-Ethylhexyl) Phthalate by a novel Enterobacter spp. Strain YC-IL1 Isolated from Polluted Soil, Mila, Algeria

Di-(2-ethylhexyl) phthalate (DEHP) is one of the phthalic acid ester representatives and is mainly used as a plasticizer to endow polyvinyl chloride plastics with desirable physical properties. It is synthesized in massive amounts worldwide. Many studies have proved the adverse effects of DEHP on human health and wildlife. DEHP is labeled as an endocrine disruptor which causes human reproductive problems. Enterobacter spp. YC-IL1, a novel isolated strain from contaminated soil, was identified by 16S rRNA gene analysis and electronic microscope. It is capable of efficiently degrading DEHP (100%) and a wide range of phthalic acid ester PAEs, particularly those containing side chains with branches, or ring structures such as dutylbenzyl phthalate and dicyclohexyl phthalate, which are hard to degrade, with, respectively, 81.15% and 50.69% degradation after 7 days incubation. YC-IL1 is an acido-tolerant strain which remained in pH values lower than pH 5.0 with the optimum pH 7.0 and temperature 30 °C. The DEHP metabolites were detected using HPLC-QQQ and then the degradation pathway was tentatively proposed. Strain YC-IL1 showed high DEHP degradation rate in artificially contaminated soil with 86% removed in 6 days. These results indicate the application potential of YC-IL1 in bioremediation of PAE-polluted sites, even the acidic ones.

Efficient degradation of ivermectin by newly isolated Aeromonas taiwanensis ZJB-18,044

Ivermectin (IVM) is a widely used antiparasitic agent and acaricide. Despite its high efficiency against nematodes and arthropods, IVM may pose a threat to the environment due to its ecotoxcity. In this study, degradation of IVM by a newly isolated bacterium Aeromonas taiwanensis ZJB-18,044 was investigated. Strain ZJB-18,044 can completely degrade 50 mg/L IVM in 5 d with a biodegradation ability of 0.42 mg/L/h. Meanwhile, it exhibited high tolerance (50 mg/L) to doramectin, emamectin, rifampicin, and spiramycin. It can also efficiently degrade doramectin, emamectin, and spiramycin. The IVM degradation of strain ZJB-18,044 can be inhibited by erythromycin, azithromycin, spiramycin or rifampicin. However, supplement of carbonyl cyanide m-chlorophenylhydrazone, an uncoupler of oxidative phosphorylation, can partially recover the IVM degradation. Moreover, strain ZJB-18,044 cells can pump out excess IVM to maintain a low intracellular IVM concentration. Therefore, the IVM tolerance of strain ZJB-18,044 may be due to the regulation of the intracellular IVM concentration by the activated macrolide efflux pump(s). With the high IVM degradation efficiency, A. taiwanensis ZJB-18,044 may serve as a bioremediation agent for IVM and other macrolides in the environment.

Biodegradation of Phenol by Rhodococcus sp. Strain SKC: Characterization and Kinetics Study

This study focuses on the kinetics of a pure strain of bacterium Rhodococcus sp. SKC, isolated from phenol-contaminated soil, for the biodegradation of phenol as its sole carbon and energy source in aqueous medium. The kinetics of phenol biodegradation including the lag phase, the maximum phenol degradation rate, maximum growth rate (R_m) and maximum yield coefficient (Y) for each S_i (initial phenol concentration, mg/L) were fitted using the Gompertz and Haldane models of substrate inhibition (R² > 0.9904, RMSE < 0.00925). The values of these parameters at optimum conditions were μ_max = 0.30 h⁻¹, K_s = 36.40 mg/L, and K_i = 418.79 mg/L, and that means the inhibition concentration of phenol was 418.79 mg/L. By comparing with other strains of bacteria, Rhodococcus sp. SKC exhibited a high yield factor and tolerance towards phenol. This study demonstrates the potential application of Rhodococcus sp. SKC for the bioremediation of phenol contaminate.

Impacts of anthropogenic activities on spatial variations of phthalate esters in water and suspended particulate matter from China's lakes

In the largest developing country, China, plastic has become a serious environmental issue because of its overuse and non-treatment. In fact, plasticizers, such as phthalate esters (PAEs), are more toxic than plastic, and their global awareness is rising. To determine the response of sensitive PAE congeners to the anthropogenic activities in a typical lake ecosystem of China, in the present study, 12 PAEs in the water and the suspended particulate matter (SPM) phases of 46 lakes in China were measured. The concentrations of all the Σ₁₂ PAEs in water and SPM phases ranged from 3.647 to 65.618 μg/L and 0.175 to 10.921 μg/L, respectively. Di-n-butyl phthalate (DnBP) was the predominant PAEs in the water phase, whereas diisobutyl phthalate (DIBP), DnBP, and bis(2-ethylhexyl) phthalate (DEHP) were the dominating PAEs in the SPM phase. Forty-six lakes were divided into four groups based on the anthropogenic activity intensities. The PAEs in both the water and SPM phases had increasing tendency along the human activity gradient. DIBP appears to be a sensitive PAE indicator that could distinguish the lake regions with different human industrial and agricultural activities. Dimethyl phthalate (DMP) and diethyl phthalate (DEP) are intensely affected by industrial development. DnBP and DEHP were positively correlated with agricultural activities, including the use of films and pesticides. It is suggested to control the addition and usage of PAEs in agricultural activities and improve their removal rates in industrial wastewater to reduce the PAE pollution in the water bodies in the environment management of China.

Metabolic process of di-n-butyl phthalate (DBP) by Enterobacter sp. DNB-S2, isolated from Mollisol region in China

The accumulation of phthalate acid esters (PAEs) in the environment has aroused a global concern. Microbial degradation is the most promising method for removing PAEs from polluted environment. Di-n-butyl phthalate (DBP) is one of the most widely used PAEs. In this study, a highly efficient DBP-degrading strain, Enterobacter sp. DNB-S2 was isolated from Mollisol in northeast China, and the degradation rate of 500 mg L^-1 DBP reached 44.10% at 5 °C and 91.08% at 50 °C within 7 days. A new intermediate, n-butyl benzoate BP, was detected, implying a new degradation pathway. The complete genome of the strain DNB-S2 was successfully sequenced to comprehensively understand of the entire DBP catabolic process. Key genes were proposed to be involved in DBP degradation, such as esterases, 3,4-dihydroxybenzoate decarboxylase and catechol 2,3-dioxygenase genes. Intermediate-utilization tests and real-time quantitative polymerase chain reaction (RT-qPCR) validated the proposed DBP catabolic pathway. The aboriginal bacterium DNB-S2 is a promising germplasm for restoring PAE-contaminated Mollisol regions at low temperature. This study provides novel insight into the catabolic mechanisms and abundant gene resources of PAE biodegradation.

Advanced Rhodococcus Biocatalysts for Environmental Biotechnologies

The review is devoted to biocatalysts based on actinobacteria of the genus Rhodococcus, which are promising for environmental biotechnologies. In the review, biotechnological advantages of Rhodococcus bacteria are evaluated, approaches used to develop robust and efficient biocatalysts are discussed, and their relevant applications are given. We focus on Rhodococcus cell immobilization in detail (methods of immobilization, criteria for strains and carriers, and optimization of process parameters) as the most efficient approach for stabilizing biocatalysts. It is shown that advanced Rhodococcus biocatalysts with improved working characteristics, enhanced stress tolerance, high catalytic activities, human and environment friendly, and commercially viable are developed, which are suitable for wastewater treatment, bioremediation, and biofuel production.

Whole Cell Actinobacteria as Biocatalysts

Production of fuels, therapeutic drugs, chemicals, and biomaterials using sustainable biological processes have received renewed attention due to increasing environmental concerns. Despite having high industrial output, most of the current chemical processes are associated with environmentally undesirable by-products which escalate the cost of downstream processing. Compared to chemical processes, whole cell biocatalysts offer several advantages including high selectivity, catalytic efficiency, milder operational conditions and low impact on the environment, making this approach the current choice for synthesis and manufacturing of different industrial products. In this review, we present the application of whole cell actinobacteria for the synthesis of biologically active compounds, biofuel production and conversion of harmful compounds to less toxic by-products. Actinobacteria alone are responsible for the production of nearly half of the documented biologically active metabolites and many enzymes; with the involvement of various species of whole cell actinobacteria such as Rhodococcus, Streptomyces, Nocardia and Corynebacterium for the production of useful industrial commodities.

The phyllosphere indigenous microbiota of Brassica campestris L. change its diversity in responding to di-n-butyl phthalate pollution

In this study, the effects of di-n-butyl phthalate (DBP) on the phyllosphere bacterial community of field mustard (Brassica campestris L.) at the five-leaf stage were investigated. The indigenous alpha-diversity of the phyllosphere bacteria was altered after spraying with different concentrations of DBP. Shannon diversity indices were significantly changed on day 5 after treatment at DBP concentrations > 400 mg L^-1 (P > 0.05). Nevertheless, the difference between treatment and control was not significant on day 9 after DBP treatment (P > 0.05). Exposure to DBP resulted in a decrease in Proteobacteria and Firmicutes, and an increase in Actinobacteria at all sampling intervals. These changes included significant increases in the relative abundance of Paracoccus and Rhodococcus, and significant decreases in that of Pseudomonas, Exiguobacterium, an unclassified genus of Pseudomonadaceae, and an unclassified genus of Enterobacteriaceae. This study provides new evidence for the possibility of using phyllosphere microbiota to remediate DBP contamination.

Biodegradation pathway of di-(2-ethylhexyl) phthalate by a novel Rhodococcus pyridinivorans XB and its bioaugmentation for remediation of DEHP contaminated soil

A novel bacterial strain designated as Rhodococcus pyridinivorans XB, capable of utilizing various endocrine disruptor phthalates or phthalic acid (PA) as sole source of carbon and energy, was isolated from activated sludge. Under the optimal culture conditions (pH 7.08, 30.4 °C, inoculum size (OD_{600 nm}) of 0.6) obtained by response surface methodology, di-(2-ethylhexyl) phthalate (DEHP, 200 mg/L) could be degraded by strain XB with a removal rate of 98% within 48 h. Under the observation of an atomic force microscope, it was confirmed that DEHP did not inhibit the growth of strain XB which might produce some extracellular polymeric substances as a response to DEHP stress, resulting in rapid degradation of DEHP. At initial concentrations of 50-800 mg/L DEHP, its degradation curves were well fitted with the first-order kinetic model, and the half-life of DEHP degradation varied from 5.44 to 23.5 h. The degradation intermediates of DEHP were identified by both GC-MS and high performance liquid chromatography-time of flight-mass spectrometry (HPLC-TOF-MS). Significant up-regulation was observed for the relative expression levels of genes (i.e., phthalate hydrolase, PA 3,4-dioxygenase, protocatechuate 3,4-α and 3,4-β dioxygenase) involved in DEHP degradation determined by real-time quantitative PCR (RT-qPCR). A DEHP biodegradation pathway by strain XB was proposed based on the identified intermediates and the degrading genes. Bioaugmentation of DEHP-contaminated soils with strain XB could efficiently promote DEHP removal, offering great potential in bioremediation of DEHP-contaminated environment.

Functional genomic analysis of phthalate acid ester (PAE) catabolism genes in the versatile PAE-mineralising bacterium Rhodococcus sp. 2G

Microbial degradation is considered the most promising method for removing phthalate acid esters (PAEs) from polluted environments; however, a comprehensive genomic understanding of the entire PAE catabolic process is still lacking. In this study, the repertoire of PAE catabolism genes in the metabolically versatile bacterium Rhodococcus sp. 2G was examined using genomic, metabolic, and bioinformatic analyses. A total of 4930 coding genes were identified from the 5.6 Mb genome of the 2G strain, including 337 esterase/hydrolase genes and 48 transferase and decarboxylase genes that were involved in hydrolysing PAEs into phthalate acid (PA) and decarboxylating PA into benzoic acid (BA). One gene cluster (xyl) responsible for transforming BA into catechol and two catechol-catabolism gene clusters controlling the ortho (cat) and meta (xyl &mhp) cleavage pathways were also identified. The proposed PAE catabolism pathway and some key degradation genes were validated by intermediate-utilising tests and real-time quantitative polymerase chain reaction. Our results provide novel insight into the mechanisms of PAE biodegradation at the molecular level and useful information on gene resources for future studies.

Treatment of olive mill wastewater through employing sequencing batch reactor: performance and microbial diversity assessment

This work describes the performance of a sequencing batch reactor (SBR) and the involvement of a novel reconstituted bacterial consortium in olive mill wastewater (OMW) treatment. The organic loading rate applied to the SBR was serially increased in terms of initial COD from 10 to 75 g L^-1 to allow gradual acclimatization of activated sludge to high concentrations of toxic compounds in OMW. After the acclimatization period, up to 60% of the total COD content were effectively biodegraded from OMW at 75 g L^-1 COD within 30 day hydraulic retention time. The diversity and community composition of cultivable bacteria participating in the aerobic process of treating OMW were further assessed. A total of 91 bacterial strains were isolated from the reactor and analyzed by amplification of the 16S-23S rRNA internal transcribed spacer (ITS) region and by 16S rRNA gene sequencing. The most abundant phylum was Firmicutes (57.1%) followed by Proteobacteria (35.2%) and Actinobacteria (7.7%). The use of the Biolog® Phenotype Microarray system to evaluate the ability of isolated strains to utilize OMW phenolic compounds is reported in this work for the first time. Interestingly, results showed that all species tested were able to utilize phenolics as sole carbon and energy sources. The removals of COD and phenolics from undiluted OMW by the reconstituted bacterial consortium were almost similar to those obtained by the acclimatized activated sludge, which suggest that cultivable bacteria play the major role in OMW biodegradation. Phytotoxicity assays using tomato seeds showed a significant improvement of seed germination values for treated OMW. Our overall results suggest that the novel developed bacterial consortium could be considered as a good prospect for phenolics-rich wastewaters bioremediation applications.

Excellent Degradation Performance of a Versatile Phthalic Acid Esters-Degrading Bacterium and Catalytic Mechanism of Monoalkyl Phthalate Hydrolase

Despites lots of characterized microorganisms that are capable of degrading phthalic acid esters (PAEs), there are few isolated strains with high activity towards PAEs under a broad range of environmental conditions. In this study, Gordonia sp. YC-JH1 had advantages over its counterparts in terms of di(2-ethylhexyl) phthalate (DEHP) degradation performance. It possessed an excellent degradation ability in the range of 20–50 °C, pH 5.0–12.0, or 0–8% NaCl with the optimal degradation condition 40 °C and pH 10.0. Therefore, strain YC-JH1 appeared suitable for bioremediation application at various conditions. Metabolites analysis revealed that DEHP was sequentially hydrolyzed by strain YC-JH1 to mono(2-ethylhexyl) phthalate (MEHP) and phthalic acid (PA). The hydrolase MphG1 from strain YC-JH1 hydrolyzed monoethyl phthalate (MEP), mono-n-butyl phthalate (MBP), mono-n-hexyl phthalate (MHP), and MEHP to PA. According to molecular docking and molecular dynamics simulation between MphG1 and monoalkyl phthalates (MAPs), some key residues were detected, including the catalytic triad (S125-H291-D259) and the residues R126 and F54 potentially binding substrates. The mutation of these residues accounted for the reduced activity. Together, the mechanism of MphG1 catalyzing MAPs was elucidated, and would shed insights into catalytic mechanism of more hydrolases.

Carbon isotopic fractionation during biodegradation of phthalate esters in anoxic condition

Here we evaluate the quantitative relationship between carbon isotopic fractionation and anoxic biodegradation of phthalate esters (PAEs), a kind of endocrine disruptors. The stable carbon isotope delta values (δ(13)C) of 4 PAEs, i.e. di-methyl phthalate (DMP), di-ethyl phthalate (DEP), di-n-butyl phthalate (DBP), and di-iso-butyl phthalate (DiBP), were analyzed during biodegradation by a pure bacteria strain isolated from the shallow aquifer sediment in anoxic condition. Results showed that the carbon isotopic fractionation in the initial degradation of PAEs was well-described by the Rayleigh equation model with R(2) from 0.8885 to 0.9821. The carbon isotopic fractionation (ε) for DMP and DEP were -4.6±0.4‰ and -2.9±0.1‰, respectively, while DBP and DiBP showed limited isotopic fractionation. A linear relationship between ε values and the total carbon atoms present in straight-carbon-chain PAE molecules with R(2) of 0.9918. The apparent kinetic isotope effects (AKIEs) were calculated for proposed 4 initial transformation pathways of PAEs. The high carbon AKIEs of 1.048 and 1.036 were obtained for single enzymatic hydrolysis of DMP and DEP, respectively, and fell in the expected KIE range of 1.03-1.09. However, the intrinsic carbon isotope effects for enzymatic hydrolysis of DBP and DiBP might be masked.