Biodegradation of phenol and 4-chlorophenol by the yeast Candida tropicalis

Co-metabolic biodegradation of 4-chlorophenol by photosynthetic bacteria

ABSTRACTEnvironmental contamination by 4-chlorophenol (4-CP) is a major concern. Photosynthetic bacteria have the ability to biodegrade 4-CP under dark aerobic conditions. In this study, we found that using different carbon sources (i.e. glucose, sodium acetate, sodium propionate sucrose, and malic acid) as co-metabolic substrates accelerated the biodegradation of 4-CP, and this acceleration was especially pronounced in the glucose treatment. A maximum degradation rate of 96.99% was reached under a concentration of 3.0 g·L^-1 after 6 days of culture. The optimum conditions were pH 7.5, a temperature of 30°C, and a rotation speed of 135 rpm. The biodegradation of 4-CP was achieved at a range of salinities (0-3.0% NaCl, w/v). The biodegradation kinetics agreed with the Haldane model, and the kinetic constants were r_max = 0.14 d^-1, K_m = 33.9 mg·L^-1, and K_i = 159.6 mg·L^-1. Additionally, the coexistence of phenol or 2,4-dichlorophenol (2, 4-DCP) had a certain impact on the degradation of 4-CP under dark aerobic conditions. When the coexisting phenol concentration reached 100 mg·L^-1, the maximum degradation rate of 4-CP reached 90.20%. The degradation rate of 4-CP decreased as the concentration of coexisting 2, 4-DCP increased.

Phenol biodegradation by Acinetobacter radioresistens APH1 and its application in soil bioremediation

Phenol accounts for a large proportion of the contamination in industrial wastewater discharged from chemical plants due to its wide use as a raw chemical. Residual phenol waste in water and soil significantly endangers human health and the natural environment. In this study, an Acinetobacter radioresistens strain, APH1, was isolated and identified for its efficient capability of utilizing phenol as sole carbon source for growth. A draft genome sequence containing 3,290,330 bases with 45 contigs was obtained, and 22 genes were found to be involved in phenol metabolism and 51 putative drug-resistance genes were annotated by genomic analysis. The optimal conditions for cell culture and phenol removal were determined to be 30 °C, pH 6.0, and a phenol concentration of 500 mg/L; the upper limit of phenol tolerance was 950 mg/L. Based on GC-MS analysis, the key metabolites including cis,cis-muconic acid, catechol, and succinic acid were detected. During bioremediation experiment using 450 mg/kg (dry weight) of phenol-contaminated soil, the strain APH1 removed 99% of the phenol within 3 days. According to microbial diversity analysis, the microbial abundance of Chungangia, Bacillus, Nitrospira, Lysinibacillus, and Planomicrobium increased after the addition of phenol. Furthermore, at day 23, the abundance of strain APH1 was greatly reduced, and the microbial diversity and structure of the whole microbial community were gradually recovered, indicating that strain APH1 would not affect this microbial ecosystem. These findings provide insights into the bioremediation of soil contaminated with phenol.

Biodegradation of high concentration phenol using sugarcane bagasse immobilized Candida tropicalis PHB5 in a packed-bed column reactor

Biodegradation of phenolic compounds in wastewater can be effectively carried out in packed bed reactors (PBRs) employing immobilized microorganisms. A low-cost, reusable immobilization matrix in PBR can provide economic advantages in large scale removal of high concentration phenol. In this study, we evaluated the efficiency and reusability of sugarcane bagasse (SCB) as a low-cost immobilization support for high strength phenol removal in recirculating upflow PBR. An isolated yeast Candida tropicalis PHB5 was immobilized onto the SCB support and packed into the reactor to assess phenol biodegradation at various influent flow rates. Scanning electron microscopy exhibited substantial cell attachment within the pith and onto the fibrous strand surface of the SCB support. The PBR showed 97% removal efficiency at the initial phenol concentration of 2400 mg L^-1 and 4 mL min^-1 flow rate within 54 h. Biodegradation kinetic studies revealed that the phenol biodegradation rate and biodegradation rate constant were dependent on the influent flow rate. A relatively higher rate of biodegradation (64.20 mg g^-1 h^-1) was found at a flow rate of 8 mL min^-1, indicating rapid phenol removal in the PBR. Up to six successive batches (phenol removal >94%) were successfully applied in the PBR using an initial phenol concentration of 400-2400 mg L^-1 at a flow rate of 4 mL min^-1 indicating the reusability of the PBR system. The SCB-immobilized C. tropicalis could be employed as a cost-effective packing material for removal of high strength phenolic compounds in real scale PBR.

Co-biodegradation of anthracene and naphthalene by the bacterium Acinetobacter johnsonii

NAP (Naphthalene) and ANT (anthracene) usually co-exist in environment and possessed interactional effects on their biodegradation in environment. Presently, a strain of Acinetobacter johnsonii was employed to degrade NAP and ANT in single- and dual-substrate systems. NAP was utilized as prefer substrate by cells to accelerate ANT biodegradation. As much as 200 mg L^-1 ANT could be entirely degraded with 1,500 mg L^-1 NAP, which was beyond bacterial potential in single substrate system. Especially, the shortest biodegradation period (103 h) for ANT was observed with the presence of 50 mg L^-1 NAP. By contrast, ANT showed strong inhibition on NAP degradation, while the peak biodegradation of 1,950 mg L^-1 NAP with 50 mg L^-1 ANT could still proceed. By introducing an inhibition constant parameter to fit the inhibition on cells, modeling indicated the substrate inhibition for NAP and ANT over the concentrations of 174 and 49 mg L^-1, respectively. Furthermore, enzyme assay revealed the pathway of meta fission in NAP biodegradation due to the appearance of catechol 2,3-dioxygenase activity, and low-level lipase excretion was also found in both NAP and ANT biodegradation, but hardly affect NAP and ANT biodegradation in the present study. To research the interplay of NAP and ANT is conducive to targeted decontamination.

[Yeasts from the CTG clade (Candida clade): Biology, impact in human health, and biotechnological applications]

Among the subdivision of Saccharomycotina (ascomycetes budding yeasts), the CTG clade (formerly the Candida clade) includes species that display a particular genetic code. In these yeasts, the CTG codon is predominantly translated as a serine instead of a leucine residue. It is now well-known that some CTG clade species have a major impact on human and its activities. Some of them are recognized as opportunistic agents of fungal infections termed candidiasis. In addition, another series of species belonging to the CTG clade draws the attention of some research groups because they exhibit a strong potential in various areas of biotechnology such as biological control, bioremediation, but also in the production of valuable biocompounds (biofuel, vitamins, sweeteners, industrial enzymes). Here we provide an overview of recent advances concerning the biology, clinical relevance, and currently tested biotechnological applications of species of the CTG clade. Future directions for scientific research on these particular yeasts are also discussed.

Efficacy of free and encapsulated Bacillus lichenformis strain SL10 on degradation of phenol: A comparative study of degradation kinetics

The present study exemplifies phenol degradation efficacy of the free and encapsulated bacterial isolate, explored the degradation kinetics and storage stability in detail. In brief, isolation, identification and phenol degradation potential of the bacterial made from wastewater treated sludge samples. The organism identified as B. licheniformis demonstrates phenol degradation at a concentration more than 1500 ppm. Optimization of environmental parameters reduces the time taken for degradation considerably. The organism has further been encapsulated using whey protein and the efficacy of encapsulated species suggested that encapsulation protects the cells from high concentration of phenol and at the same time expedite the degradation of the chosen pollutant at appreciable level. The encapsulated species effectively degrade 3000 ppm concentration of phenol within 96 h of incubation. Both pH and temperature stability observed in the encapsulated species suggests the effectiveness of the encapsulation. The encapsulated cells displayed storage stability for a four week period at 4 C and reusability up to three exposures. Degradation effected through intracellular catechol 2,3 dioxygenase. In conclusion, encapsulation of B. licheniformis (i) protects the cells from direct exposure to toxic pollutants; (ii) facilitates the field scale application and (iii) eliminate the practical difficulties in handling wet biomass in field application and assures the best possible way of remediating the phenol contaminated soil.

Catabolism of Phenol and Its Derivatives in Bacteria: Genes, Their Regulation, and Use in the Biodegradation of Toxic Pollutants

Phenol and its derivatives (alkylphenols, halogenated phenols, nitrophenols) are natural or man-made aromatic compounds that are ubiquitous in nature and in human-polluted environments. Many of these substances are toxic and/or suspected of mutagenic, carcinogenic, and teratogenic effects. Bioremediation of the polluted soil and water using various bacteria has proved to be a promising option for the removal of these compounds. In this review, we describe a number of peripheral pathways of aerobic and anaerobic catabolism of various natural and xenobiotic phenolic compounds, which funnel these substances into a smaller number of central catabolic pathways. Finally, the metabolites are used as carbon and energy sources in the citric acid cycle. We provide here the characteristics of the enzymes that convert the phenolic compounds and their catabolites, show their genes, and describe regulatory features. The genes, which encode these enzymes, are organized on chromosomes and plasmids of the natural bacterial degraders in various patterns. The accumulated data on similarities and the differences of the genes, their varied organization, and particularly, an astonishingly broad range of intricate regulatory mechanism may be read as an exciting adventurous book on divergent evolutionary processes and horizontal gene transfer events inscribed in the bacterial genomes. In the end, the use of this wealth of bacterial biodegradation potential and the manipulation of its genetic basis for purposes of bioremediation is exemplified. It is envisioned that the integrated high-throughput techniques and genome-level approaches will enable us to manipulate systems rather than separated genes, which will give birth to systems biotechnology.

Experimental and kinetic study on the cometabolic biodegradation of phenol and 4-chlorophenol by psychrotrophic Pseudomonas putida LY1

This study investigated the kinetics of phenol and 4-chlorophenol (4-CP) biodegradation by a cold-adapted bacteria, Pseudomonas putida LY1, isolated from Songhua River sediment. The results showed that P. putida LY1 cannot grow on 4-CP as a sole carbon source. P. putida LY1 had the potential to cometabolic biodegrade phenol and 4-CP in a wide range of temperature (varying from 5 to 35 °C) with the optimal temperature around 25 °C. Mixture of phenol and 4-CP were completely removed at two 4-CP concentrations (15 and 40 mg/L) over a wide range of phenol (20-400 mg/L) concentrations, whereby the ratio of 4-CP/biomass (S 2/X) was lower than 0.03. The kinetic models of cometabolic biodegradation of phenol and 4-CP were proposed, considering the growth and nongrowth substrate inhibition. These models successfully simulate the processes of cometabolic degradation of phenol and 4-CP.

Kinetics of phenol biodegradation at high concentration by a metabolically versatile isolated yeast Candida tropicalis PHB5

A highly tolerant phenol-degrading yeast strain PHB5 was isolated from wastewater effluent of a coke oven plant and identified as Candida tropicalis based on phylogenetic analysis. Biodegradation experiments with C. tropicalis PHB5 showed that the strain was able to utilize 99.4% of 2,400 mg l(-1) phenol as sole source of carbon and energy within 48 h. Strain PHB5 was also observed to grow on 18 various aromatic hydrocarbons. Haldane model was used to fit the exponential growth data and the following kinetic parameters were obtained: μ max = 0.3407 h(-1), K S = 15.81 mg l(-1), K i = 169.0 mg l(-1) (R (2) = 0.9886). The true specific growth rate, calculated from μ max, was 0.2113. A volumetric phenol degradation rate (V max) was calculated by fitting the phenol consumption data with Gompertz model and specific degradation rate (q) was calculated from V max. The q values were fitted with Haldane model, yielding following parameters: q max = 0.2766 g g(-1) h(-1), K S ' = 2.819 mg l(-1), K i ' = 2,093 (R (2) = 0.8176). The yield factor (Y X/S ) varied between 0.185 to 0.96 g g(-1) for different initial phenol concentrations. Phenol degradation by the strain proceeded through a pathway involving production of intermediates such as catechol and cis,cis-muconic acid which were identified by enzymatic assays and HPLC analysis.

Kinetic and isotherm studies of adsorption and biosorption processes in the removal of phenolic compounds from aqueous solutions: comparative study

The phenolic compounds are known by their carcinogenicity and high toxicity as well as creating unpleasant taste and odor in water resources. The present study develops a cost-effective technology for the treatment of water contaminated with phenolic compounds, including Phenol (Ph), 2-chlorophenol (2-CP), and 4-chlorophenol (4-CP). So, two sorbents, rice bran ash (RBA) and biomass of brown algae, Cystoseiraindica, were used and results were compared with the commercially granular activated carbon (GAC). The phenolic compounds were determined using a high performance liquid chromatography (HPLC) under batch equilibrium conditions. The effects of contact time, pH, initial adsorbate concentration, and adsorbent dosages on the removal efficiency were studied. The adsorption data were simulated by isotherm and kinetic models. Results indicated that RBA and GAC had the lowest efficiency for the removal of 2-CP, while the order of removal efficiency for C. indica biomass was as follows: 2-CP > 4-CP > phenol. The efficiency of GAC was higher than those of other adsorbents for all of the phenolic compounds. Furthermore, the adsorption capacity of RBA was found to be higher than that of C. indica biomass. The optimal initial pH for the removal of phenol, 2-CP and 4-CP was determined to be 5, 7, and 7 for RBA, GAC, and algal biomass, respectively. Kinetic studies suggested that the pseudo-second order best fitted the kinetic data.

Treatment of substituted phenol mixtures in single phase and two-phase solid-liquid partitioning bioreactors

The biological treatment of phenolics is constrained by the inherent cytotoxicity of these compounds. One method to alleviate such toxicity is to add a sequestering phase to absorb, and subsequently release, the substrate(s) to the micro-organisms; such a system is termed a Two Phase Partitioning Bioreactor. Here we have compared the performance of a TPPB, relative to single phase operation, in which a small volume (5%, v/v) of beads of the polymer Hytrel 8206 was used to treat aqueous mixtures of 2,4-dimethylphenol and 4-nitrophenol. Hytrel 8206 was selected from a range of polymers that were tested for their partition coefficients (PCs) for the target molecules, with the more hydrophobic compound (2,4-dimethylphenol) having a higher PC value (201) than 4-nitrophenol (143). Significantly increased removal rates for both substrates were demonstrated in TPPB mode relative to single phase operation. Additionally, the differential release of the compounds to the aqueous phase and their distinct PC values changed the kinetic pattern of the biotreatment system, smoothing out the cellular oxygen demand. Release of the substrates by the polymer over 60 operating cycles was virtually complete (>97%) demonstrating the reusability and robustness of the use of polymers in overcoming cytotoxicity of phenolic substrates.

Performance Evaluation of AOP/Biological Hybrid System for Treatment of Recalcitrant Organic Compounds

Process water from nuclear fuel recovery unit operations contains a variety of toxic organic compounds. The use of decontamination reagents such asCCl4together with phenolic tar results in wastewater with a high content of chlorophenols. In this study, the extent of dehalogenation of toxic aromatic compounds was evaluated using a photolytic advanced oxidation process (AOP) followed by biodegradation in the second stage. A hard-to-degrade toxic pollutant, 4-chlorophenol (4-CP), was used to represent a variety of recalcitrant aromatic pollutants in effluent from the nuclear industry. A UV-assisted AOP/bioreactor system demonstrated a great potential in treatment of nuclear process wastewater and this was indicated by high removal efficiency (>98%) under various 4-CP concentrations. Adding hydrogen peroxide (H2O2) as a liquid catalyst further improved biodegradation rate but the effect was limited by the scavenging ofOH•radicals under high concentrations ofH2O2.

Simultaneous degradation of organophosphates and 4-substituted phenols by Stenotrophomonas species LZ-1 with surface-displayed organophosphorus hydrolase

Organophosphorous hydrolase (OPH) was expressed onto the surface of a Stenotrophomonas species (LZ-1), capable of simultaneously degrading 4-substituted phenols, using the N- and C-terminal domains of ice nucleation protein (INPNC) as an anchoring motif for the first time. The engineered strain LZ-1 could degrade p-nitrophenyl-substituted organophosphates as well as their hydrolytic product, PNP, rapidly. Especially, addition of 4-CP (below 0.8 mM) significantly accelerated the complete degradation of above organophosphates (47.1, 34.0, and 40% reduction of time of paraoxon, parathion, and methyl-parathion, respectively) through the accelerated degradation of PNP due to enhanced cell growth supported by 4-CP as the carbon source. OPH could be surface-displayed at a high level without inhibition of cell growth and OPH activity in the presence of 4-CP. In soil samples, strain LZ-1 could also remove these compounds successfully. Functional display of heterologous proteins on the surface of indigenous bacteria could provide a promising technology for effective bioremediation of sites contaminated with mixed organic pollutants.

Phenol degradation by Aureobasidium pullulans FE13 isolated from industrial effluents

The degradation of phenol (2-30 mM) by free cells and by alginate-immobilized cells of Aureobasidium pullulans FE13 isolated from stainless steel effluents was studied in batch cultures with saline solution not supplemented with nutrients or yeast extract. The rate at which the immobilized cells degrade phenol was similar to the rate at which the suspended cells could degrade phenol, for a concentration of up to 16 mM of phenol. The maximum phenol volumetric degradation rate for 16 mM phenol was found to be 18.35 mg l(-1)h(-1) in the assays with free cells and 20.45 mg l(-1)h(-1) in the assays with alginate-immobilized cells, 18 mM phenol and cellular concentration of 0.176 g/l. At concentrations higher than this, an inhibitory effect was observed, resulting in the lowering of the phenol degradation rates. The immobilization was detrimental to the catechol 1,2-dioxygenase activity. However, the immobilized cells remained viable for a longer period, increasing the efficiency of phenol degradation. The yeast showed catechol 1,2-dioxygenase activity only after growth in the phenol, which was induced at phenol concentrations as low as 0.05 mM and up to 25 mM at 45 h of incubation at 30 degrees C. Phenol concentrations higher than 6mM were inhibitory to the enzyme. Addition of glucose, lactate, succinate, and benzoate reduced the rate at which phenol is consumed by cells. Our results suggest that inoculants based on immobilized cells of A. pullulans FE13 has potential application in the biodegradation of phenol and possibly in the degradation of other related aromatic compounds.

Stable isotope probing reveals Trichosporon yeast to be active in situ in soil phenol metabolism

The aim of this study was to extend the results of our previous stable isotope probing (SIP) investigation: we identified a soil fungus involved in phenol biodegradation at an agricultural field site. DNA extracts from our previous study were examined using fungi-specific PCR amplification of the 18S-28S internal transcribed spacer (ITS) region. We prepared an 80-member clone library using PCR-amplified, (13)C-labeled DNA derived from field soil that received 12 daily doses of (13)C-phenol. Restriction-fragment-length-polymorphism screening and DNA sequencing revealed a dominant clone (41% of the clone library), the ITS sequence of which corresponded to that of the fungal genus Trichosporon. We successfully grew and isolated a white, filamentous fungus from site soil samples after plating soil dilutions on mineral salts agar containing 250 p.p.m. phenol. Restreaking on both yeast extract-peptone-galactose and Sabouraud dextrose agar plates led to further purification of the fungus, the morphological characteristics of which matched those of the genus Trichosporon. The ITS sequence of our isolated fungus was identical to that of a clone from our SIP-based library, confirming it to be Trichosporon multisporum. High-performance liquid chromatography and turbidometeric analyses showed that the culture was able to metabolize and grow on 200 p.p.m. phenol in an aqueous mineral salts medium within 24 h at room temperature. Gas chromatography-mass spectrometry analysis of (13)CO(2) respiration from laboratory soil incubations demonstrated accelerated phenol mineralization in treatments inoculated with T. multisporum. These findings show that T. multisporum actively degraded phenol in our field-based, soil experiments.