Degradation and O-methylation of chlorinated phenolic compounds by Rhodococcus and Mycobacterium strains

Chemotaxis-mediated degradation of PAHs and heterocyclic PAHs under low-temperature stress by Pseudomonas fluorescens S01: Insights into the mechanisms of biodegradation and cold adaptation

As wellknown persistent contaminants, polycyclic aromatic hydrocarbons (PAHs) and heterocyclic polyaromatic hydrocarbons (Heterocyclic PAHs)'s fates in cryogenic environments are remains uncertain. Herein, strain S01 was identified as Pseudomonas fluorescens, a novel bacterium tolerant to low temperature and capable of degrading PAHs and heterocyclic PAHs. Strain S01 exhibited growth at 5-40 ℃ and degradation rate of mixed PAHs and heterocyclic PAHs reached 52% under low-temperature. Through comprehensive metabolomic, genomic, and transcriptomic analyses, we reconstructed the biodegradation pathway for PAHs and heterocyclic PAHs in S01 while investigating its response to low temperature. Further experiments involving deletion and replacement of methyl-accepting chemotaxis protein (MCP) confirmed its crucial role in enabling strain S01's adaptation to dual stress of low temperature and pollutants. Additionally, our analysis revealed that MCP was upregulated under cold stress which enhanced strain S01's motility capabilities leading to increased biofilm formation. The establishment of biofilm promoted preservation of distinct cellular membrane stability, thereby enhancing energy metabolism. Consequently, this led to heightened efficiency in pollutant degradation and improved cold resistance capabilities. Our findings provide a comprehensive understanding of the environmental fate of both PAHs and heterocyclic PAHs under low-temperature conditions while also shedding light on cold adaptation mechanism employed by strain S01.

A study into the diversity of coral-associated bacteria using culture-dependent and culture-independent approaches in coral Dipsastraea favus from the Gulf of Kutch

Corals harbour ~25 % of the marine diversity referring to biodiversity hotspots in marine ecosystems. Global efforts to find ways to restore the coral reef ecosystem from various threats can be complemented by studying coral-associated bacteria. Coral-associated bacteria are vital components of overall coral wellbeing. We explored the bacterial diversity associated with coral Dipsastraea favus (D. favus) collected from the Gulf of Kutch, India, using both culture-dependent and metagenomic approaches. In both approaches, phylum Proteobacteria, Firmicutes, and Actinobacteria predominated, comprising the genera Vibrio, Bacillus, Shewanella, Pseudoalteromonas, Exiguobacterium and Streptomyces. Moreover, the majority of culturable isolates showed multiple antibiotic resistance index ≥0.2. In this study, specific bacterial diversity associated with coral sp. D. favus and its possible role in managing coral health was established. Almost 43 strains from the samples were successfully cultured, creating a base for exploring these microbes for their potential use in coral conservation methods.

A critical review on environmental risk and toxic hazards of refractory pollutants discharged in chlorolignin waste of pulp and paper mills and their remediation approaches for environmental safety

Agro-based pulp and paper mills (PPMs) inevitably produce numerous refractory pollutants in their wastewater, including chlorolignin, chlorophenols, chlorocatechols, chloroguaiacol, cyanide, furan, dioxins, and other organic compounds, as well as various heavy metals, such as nickel (Ni), zinc (Zn), chromium (Cr), iron (Fe), lead (Pb), arsenic (As), etc. These pollutants pose significant threats to aquatic and terrestrial life due to their cytogenotoxicity, mutagenicity, impact on sexual organs, hormonal interference, endocrine disruption, and allergenic response. Consequently, it is crucial to reclaim pulp paper mill wastewater (PPMW) with high loads of refractory pollutants through effective and environmentally sustainable practices to minimize the presence of these chemicals and ensure environmental safety. However, there is currently no comprehensive published review providing up-to-date knowledge on the fate of refractory pollutants from PPMW in soil and aquatic environments, along with valuable insights into the associated health hazards and remediation methods. This critical review aims to shed light on the potential adverse effects of refractory pollutants from PPMW on natural ecosystems and living organisms. It explores existing effective treatment technologies for remediating these pollutants from wastewater, highlighting the advantages and disadvantages of each approach, all in pursuit of environmental safety. Special emphasis is placed on emerging technologies used to decontaminate wastewater discharged from PPMs, ensuring the preservation of the environment. Additionally, this review addresses the major challenges and proposes future research directions for the proper disposal of PPMW. It serves as a comprehensive source of knowledge on the environmental toxicity and risks associated with refractory pollutants in PPMW, making it a valuable reference for policymakers and researchers when selecting appropriate technologies for remediation. The scientific community, concerned with mitigating the widespread risks posed by refractory pollutants from PPMs, is expected to take a keen interest in this review.

A review on triclosan in wastewater: Mechanism of action, resistance phenomenon, environmental risks, and sustainable removal techniques

Triclosan, belonging to the bisphenols, is a known antiseptic broad-spectrum biocide. It has a very wide range of applications, both in health care and in the household. Triclosan enters the environment, both water bodies and soil, because of its high prevalence and the ability to accumulation. Excessive use of antimicrobial formulations may cause the generation of resistance among microorganisms. Reduced susceptibility to triclosan is observed more frequently and in an expanded group of microorganisms and is conditioned by a number of different mechanisms occurring on the molecular level. Conventional wastewater treatment processes are not always able to provide a reliable barrier to triclosan. Therefore, additional advanced treatment technologies are being considered in areas, where a triclosan contamination problem has been identified. Removal of triclosan from wastewater is carried out using different biological and chemical techniques; however, it should be pointed out that physico-chemical methods often generate toxic by-products. Toxicity of triclosan and its degradation products, bacterial resistance to this compound, and evident problems with triclosan elimination from wastewater are currently the main problems faced by companies creating products containing triclosan. PRACTITIONER POINTS: Triclosan is an emerging pollutant in the environment because of its ability to accumulation and high prevalence. Reduced susceptibility to triclosan is being observed more frequently. Conventional wastewater treatment processes are not always able to provide a reliable barrier to triclosan. Additional advanced treatment technologies should be implemented to remove triclosan from wastewater.

Novel and Simple Method for Quantification of 2,4,6-Trichlorophenol with Microbial Conversion to 2,4,6-Trichloroanisole

Contamination with 2,4,6-trichloroanisole (TCA) often causes taste and odor (T&O) problems in drinking water due to its low odor threshold concentration. Microbial O-methylation of the precursor 2,4,6-trichlorophenol (TCP) would be the dominant mechanism for TCA formation. Simple and rapid measurement of TCP in the low concentration range is necessary to control the problems induced by TCA. In this study, the combination of microbial conversion and instrumental analysis was proposed as a method of TCP quantification. Fungi and bacteria were isolated from various water samples and examined for their ability to produce TCA from TCP. As a result, a strain exhibiting quantitative TCA production and a high growth rate was obtained and named Mycolicibacterium sp. CB14. The conversion rate of TCP to TCA by this strain was found to be high and stable (85.9 ± 5.3%), regardless of the applied TCP concentration, although within the range of 0.1-10 µg/L. The limits of detection and quantification for TCP by this proposed method were determined to be 5.2 ng/L and 17.3 ng/L, respectively. By improving the methods, Mycolicibacterium sp. CB14 could be used for the quantification of TCP at very low concentration levels, which is sufficient to manage the T&O problem caused by TCA.

Biotreatment efficiency, degradation mechanism and bacterial community structure in an immobilized cell bioreactor treating triclosan-rich wastewater

Biotreatment of triclosan is mainly performed in conventional activated sludge systems, which, however, are not capable of completely removing this antibacterial agent. As a consequence, triclosan ends up in surface and groundwater, constituting an environmental threat, due to its toxicity to aquatic life. However, little is known regarding the diversity and mechanism of action of microbiota capable of degrading triclosan. In this work, an immobilized cell bioreactor was setup to treat triclosan-rich wastewater. Bioreactor operation resulted in high triclosan removal efficiency, even greater than 99.5%. Nitrogen assimilation was mainly occurred in immobilized biomass, although nitrification was inhibited. Based on Illumina sequencing, Bradyrhizobiaceae, followed by Ferruginibacter, Thermomonas, Lysobacter and Gordonia, were the dominant genera in the bioreactor, representing 38.40 ± 0.62% of the total reads. However, a broad number of taxa (15 genera), mainly members of Xanthomonadaceae, Bradyrhizobiaceae and Chitinophagaceae, showed relative abundances between 1% and 3%. Liquid Chromatography coupled to Quadrupole Time-Of-Flight Mass Spectrometry (LC-QTOF-MS) resulted in the identification of catabolic routes of triclosan in the immobilized cell bioreactor. Seven intermediates of triclosan were detected, with 2,4-dichlorophenol, 4-chlorocatechol and 2-chlorohydroquinone being the key breakdown products of triclosan. Thus, the immobilized cell bioreactor accommodated a diverse bacterial community capable of degrading triclosan.

Triclosan and triclocarban as potential risk factors of colitis and colon cancer: Roles of gut microbiota involved

In recent decades there has been a dramatic increase in the incidence and prevalence of inflammatory bowel disease (IBD), a chronic inflammatory disease of the intestinal tissues and a major risk factor of developing colon cancer. While accumulating evidence supports that the rapid increase of IBD is mainly caused by exposure to environmental risk factors, the identities of the risk factors, as well as the mechanisms connecting environmental exposure with IBD, remain largely unknown. Triclosan (TCS) and triclocarban (TCC) are high-volume chemicals that are used as antimicrobial ingredients in consumer and industrial products. They are ubiquitous contaminants in the environment and are frequently detected in human populations. Recent studies showed that exposure to TCS/TCC, at human exposure-relevant doses, increases the severity of colitis and exacerbates colon tumorigenesis in mice, suggesting that they could be risk factors of IBD and associated diseases. The gut toxicities of these compounds require the presence of gut microbiota, since they fail to induce colonic inflammation in mice lacking the microbiota. Regarding the functional roles of the microbiota involved, gut commensal microbes and specific microbial β-glucuronidase (GUS) enzymes mediate colonic metabolism of TCS, leading to metabolic reactivation of TCS in the colon and contributing to its subsequent gut toxicity. Overall, these results support that these commonly used compounds could be environmental risk factors of IBD and associated diseases through gut microbiota-dependent mechanisms.

Efficient biodegradation of tetrabromobisphenol A by the novel strain Enterobacter sp. T2 with good environmental adaptation: Kinetics, pathways and genomic characteristics

T2, a gram-positive bacterium capable of rapidly degrading tetrabromobisphenol A (TBBPA), and affiliated with the genus Enterobacter, was isolated for the first time from sludge that had been contaminated for several years. The TBBPA degradation data fitted the first-order model well. Under optimal conditions (pH of 7, temperature of 31 °C, TBBPA concentration of 5 mg L^-1, and inoculum size of 5%), 99.4% of the initially added TBBPA was degraded after 48 h. TBBPA degradation fitted the first-order model with the half-life of 3.3 h. These results illustrated that the TBBPA degradation capability of strain T2 was significantly better than that of previously reported bacteria. A total of 17 intermediates were detected, among which five were reported for the first time. Whole-genome sequencing revealed that strain T2 had a chromosome with the total length of 4 854 376 bp and a plasmid with the total length of 21 444 bp. It harbored essential genes responsible for debromination, such as cyp450, gstB, gstA, and HADH, and genes responsible for subsequent complete mineralization, such as bioC, yrrM, Tam, and Ubil. A key protein of haloacid dehalogenases responsible for the biodegradation of TBBPA may also be involved in the regulation of TBBPA degradation in natural environment. In soil bioremediation experiments, strain T2 showed excellent environmental adaptation. It was able to biodegrade TBBPA and its typical intermediate bisphenol A efficiently. Therefore, it could potentially be applied to treat TBBPA-contaminated sites.

Biotransformation of halophenols into earthy-musty haloanisoles: Investigation of dominant bacterial contributors in drinking water distribution systems

Microorganisms in drinking water distribution systems (DWDSs) can O-methylate toxic halophenols (HPs) into earthy-musty haloanisoles (HAs). However, the dominant HA-producing bacterial species and their O-methylation properties are still unknown. In this study, eight bacterial strains from DWDS were isolated and the community abundances of the related genera in bulk water and biofilms as well as their O-methylation properties were investigated. Among the genera discovered in this study, Sphingomonas and Pseudomonas are dominant and play important roles in DWDSs. All bacteria could simultaneously convert five HPs to the corresponding HAs. Two Sphingomonas ursincola strains mainly produced 2,3,6-trichloroanisole (2,3,6-TCA) (2.48 × 10^-9-1.18 × 10^-8 ng/CFU), 2,4,6-trichloroanisole (2,4,6-TCA) (8.12 × 10^-10-3.11 × 10^-9 ng/CFU) and 2,4,6-tribromoanisole (2,4,6-TBA) (2.95 × 10^-9-3.21 × 10^-9 ng/CFU), while two Pseudomonas moraviensis strains preferred to generate 2-monochloroanisole (2-MCA) (1.19 × 10^-9-3.70 × 10^-9 ng/CFU) and 2,4-dichloroanisole (2,4-DCA) (3.81 × 10^-9-1.20 × 10^-8 ng/CFU). Among the chloramphenicol-susceptible strains, four strains contained inducible O-methyltransferases (OMTs), while the O-methylations of the others were expressed constitutively. All bacteria could use S-adenosyl methionine as methyl donor. Potential taste and odor (T & O) risks of five HAs in DWDS followed an order of 2,4,6-TBA > 2,4,6-TCA > 2,3,6-TCA > 2,4-DCA > 2-MCA. The recommended 2,4,6-TCP criteria for T & O control is 0.003-0.07 mg/L.

Modification of the Pseudomonas aeruginosa toxin 2-heptyl-1-hydroxyquinolin-4(1H)-one and other secondary metabolites by methyltransferases from mycobacteria

The opportunistic pathogen Pseudomonas aeruginosa, one of the most prevalent species in infections of the cystic fibrosis lung, produces a range of secondary metabolites, among them the respiratory toxin 2-heptyl-1-hydroxyquinolin-4(1H)-one (2-heptyl-4-hydroxyquinoline N-oxide, HQNO). Cultures of the emerging cystic fibrosis pathogen Mycobacteroides abscessus detoxify HQNO by methylating the N-hydroxy moiety. In this study, the class I methyltransferase MAB_2834c and its orthologue from Mycobacterium tuberculosis, Rv0560c, were identified as HQNO O-methyltransferases. The P. aeruginosa exoproducts 4-hydroxyquinolin-2(1H)-one (DHQ), 2-heptylquinolin-4(1H)-one (HHQ), and 2-heptyl-3-hydroxyquinolin-4(1H)-one (the 'Pseudomonas quinolone signal', PQS), some structurally related (iso)quinolones, and the flavonol quercetin were also methylated; however, HQNO was by far the preferred substrate. Both enzymes converted a benzimidazole[1,2-a]pyridine-4-carbonitrile-based compound, representing the scaffold of antimycobacterial substances, to an N-methylated derivative. We suggest that these promiscuous methyltransferases, newly termed as heterocyclic toxin methyltransferases (Htm), are involved in cellular response to chemical stress and possibly contribute to resistance of mycobacteria toward antimicrobial natural compounds as well as drugs. Thus, synthetic antimycobacterial agents may be designed to be unamenable to methyl transfer. ENZYMES: S-adenosyl-l-methionine:2-heptyl-1-hydroxyquinolin-4(1H)-one O-methyl-transferase, EC 2.1.1.

Removal and transformation pathways of benzothiazole and benzotriazole in membrane bioreactors treating synthetic municipal wastewater

Lab-scale membrane bioreactors (MBRs), with aerated activated sludge and internal microfiltration module, were used for the treatment of municipal wastewater containing high, yet environmentally relevant, concentrations of benzothiazole (BT) and benzotriazole (BTA). These high production volume compounds are commonly used in the industry and households, and therefore occur ubiquitously in municipal wastewater and the aquatic environment. The aim of this study was to assess the removal of BT and BTA from synthetic municipal wastewater in MBRs and to estimate the contribution of elimination processes and to identify potential biotransformation products. The overall removal of BT and BTA was high, and after the adaptation period, it reached 99.8% and 97.2%, respectively, but recurring periods of unstable BTA removal occurred. The removal due to biotransformation was 88% for BT and 84% for BTA and the disposal with waste sludge accounted for only <1% of the removed load. The remaining fraction of the removed load of BT and BTA was attributed to be retained by phenomena associated with membrane fouling. The adaptation process was reflected in multifold increase in biodegradation kinetic coefficient (k_biol) for BT (reported for the first time) and BTA. Biodegradation was attributed to catabolic mechanism rather than to cometabolism. Hydroxylation was observed to be the main transformation reaction for BT, whereas for BTA hydroxylation, methylation and cleavage of benzene ring were noted. This study has shown the feasibility of treating municipal wastewater with high concentrations of BT and BTA in MBRs and identified potential challenges for the removal of BTA.

Pollutants released from the pulp paper industry: Aquatic toxicity and their health hazards

The pulp paper industries release wastewater containing very complex organic and inorganic pollutants. These pollutants are discharged mainly pulping and bleaching process during paper manufacturing. The main gaseous pollutants hydrogen sulfides, sodium sulfide, methyl mercaptan, sulfur, and chlorine dioxide is reported for chronic, respiratory disorder and irritation to skin, eyes and cardiac problem along with nausea and headache. The major inorganic pollutants include ferrous, copper, zinc, nickel, and magnesium, which is reported for neurotoxicity, toxic to juvenile channel catfish (Ictalurus punctatus) and Accumulation to gill > liver > ovary > muscle. The detected major organic and inorganic pollutants are hexadecanoic acids, octacosane, β-sitosterol trimethylsilyl ether, 1-tetradecane, 2-methoxy phenol, trichlorocatechol, tetrachlorocatechol, chlorophenols, chloroguaiacols, chlorosyringols, chlorocatechols, terpenes, methanol, phenol, alkylated phenols, decalone, benzoic acid, abietic acid, and dehydroabietic acid. Several of these compounds are reported as endocrine-disrupting chemicals (EDCs). Therefore, direct toxicity of effluent to the reproductive system in aquatic flora and fauna are reported. Several reports have highlighted reduced gonad size, change in secondary sexual character, delayed maturity and suppression of sex hormone in fish rainbow trout (Oncorhynchus mykiss) and mosquitofish (Gambusia holbrooki) further the in-vitro studies of organic compounds on fish, Salmonella typhimurium, Vibrio fischeri, and Saccharomyces have shown inhibition in growth and luminescence properties. The presence of organic and inorganic pollutants in pulp paper industry wastewater causes phytotoxicity chromosomal aberration in Allium cepa. Thus the manuscript has concluded that detected pollutants produced foul odors and cause hermaphroditism in fish, hepatotoxicity and mutagenic effect. In addition, the growth of coliform bacteria in River and other aquatic resources has been reported due to contamination of PPI effluent. The studies also highlighted the presence of tannins, chlorophenols, dioxins, furans, biocide, fatty acids, and resin acids along with chlorolignine compounds as persistent organic pollutants (POP), which needs special attention for pollution prevention of rivers, lakes and other aquatic resources.

Transformation of tetrabromobisphenol A by Rhodococcus jostii RHA1: Effects of heavy metals

Tetrabromobisphenol A (TBBPA) is one of the most widely used brominated flame retardants in the world but it is also a pollutant of global concern. In the present study, we studied the transformation of ¹⁴C-labeled TBBPA by a polychlorinated-biphenyl-degrading bacterium, Rhodococcus jostii RHA1 (RHA1), under oxic conditions. During the 5-day incubation, TBBPA was biotransformed rapidly first to its monomethyl ether MeO-TBBPA and then to its more hydrophobic but less toxic dimethyl ether diMeO-TBBPA. The biotransformation followed pseudo-first-order decay kinetics, with a half-life of TBBPA of 0.32 days and only 0.6% of the initially added amount being mineralized. Considering the frequent co-occurrence of TBBPA with heavy metals in the natural environment, we also investigated the effects of three heavy metals (Cd, Cu, and Fe) on the transformation of TBBPA by strain RHA1. While TBBPA transformation was not significantly altered by Cd, it was accelerated by Cu and Fe, presumably due to the effects of these two essential metals on O-methyltransferase activity. Overall, the present study showed that RHA1 is an effective transformer of TBBPA and that certain essential metals, including Cu and Fe, promote the transformation.

Removal and metabolism of triclosan by three different microalgal species in aquatic environment

Triclosan, an antimicrobial additive widely used in personal care products, has caused the contamination of various aquatic environment. Biodegradation was proved to play a vital role in the treatment of triclosan in wastewater. However, there is limited information about the metabolic pathway. In this study, three common freshwater microalgae including Chlorella pyrenoidosa (C. pyrenoidosa), Desmodesmus sp., and Scenedesmus obliquus (S. obliquus) were applied to remove and biodegrade triclosan in aqueous culture medium. High removal rate up to 99.7% was observed during the treatment of 400μgL^-1 triclosan by the three microalgae for 1day. The removal of triclosan attributed to cellular uptake by C. pyrenoidosa, and biotransformation by Desmodesmus sp. and S. obliquus. Simultaneously, triclosan metabolites resulted from hydroxylation, reductive dechlorination, or ether bond cleavage and their conjugates produced through glucosylation and/or methylation were detected in the biodegradation samples. Metabolic pathway of triclosan by algae were firstly proposed in this work, shedding light on the environmental fate of triclosan.

Chemical Modification and Detoxification of the Pseudomonas aeruginosa Toxin 2-Heptyl-4-hydroxyquinoline N-Oxide by Environmental and Pathogenic Bacteria

2-Heptyl-4-hydroxyquinoline N-oxide (HQNO), a major secondary metabolite and virulence factor produced by the opportunistic pathogen Pseudomonas aeruginosa, acts as a potent inhibitor of respiratory electron transfer and thereby affects host cells as well as microorganisms. In this study, we demonstrate the previously unknown capability of environmental and pathogenic bacteria to transform and detoxify this compound. Strains of Arthrobacter and Rhodococcus spp. as well as Staphylococcus aureus introduced a hydroxyl group at C-3 of HQNO, whereas Mycobacterium abscessus, M. fortuitum, and M. smegmatis performed an O-methylation, forming 2-heptyl-1-methoxy-4-oxoquinoline as the initial metabolite. Bacillus spp. produced the glycosylated derivative 2-heptyl-1-(β-d-glucopyranosydyl)-4-oxoquinoline. Assaying the effects of these metabolites on cellular respiration and on quinol oxidase activity of membrane fractions revealed that their EC₅₀ values were up to 2 orders of magnitude higher than that of HQNO. Furthermore, cellular levels of reactive oxygen species were significantly lower in the presence of the metabolites than under the influence of HQNO. Therefore, the capacity to transform HQNO should lead to a competitive advantage against P. aeruginosa. Our findings contribute new insight into the metabolic diversity of bacteria and add another layer of complexity to the metabolic interactions which likely contribute to shaping polymicrobial communities comprising P. aeruginosa.

Triclosan exposure, transformation, and human health effects

Triclosan (TCS) is an antimicrobial used so ubiquitously that 75% of the US population is likely exposed to this compound via consumer goods and personal care products. In September 2016, TCS was banned from soap products following the risk assessment by the US Food and Drug Administration (FDA). However, TCS still remains, at high concentrations, in other personal care products such as toothpaste, mouthwash, hand sanitizer, and surgical soaps. TCS is readily absorbed into human skin and oral mucosa and found in various human tissues and fluids. The aim of this review was to describe TCS exposure routes and levels as well as metabolism and transformation processes. The burgeoning literature on human health effects associated with TCS exposure, such as reproductive problems, was also summarized.

Why Small Differences Matter: Elucidation of the Mechanisms Underlying the Transformation of 2OH- and 3OH-Carbamazepine in Contact with Sand Filter Material

Carbamazepine (CBZ) is a worldwide used antiepileptic drug, which is metabolized to a large extent in the human body to several metabolites, including 10,11-dihydroxy-10,11-dihydrocarbamazepine (DiOHCBZ), 2-hydroxycarbamazepine (2OHCBZ), and 3-hydroxycarbamazepine (3OHCBZ). 2OHCBZ and 3OHCBZ were previously detected in raw and treated wastewater revealing their widespread emission into the aquatic environment, eventually leading to the contamination of drinking water resources. Sand filtration is frequently applied in drinking water treatment for the removal of inorganic species and suspended particles but has been shown to be capable of removing trace organic contaminants. This study focuses on the elucidation of the (bio)transformation mechanisms of 2OHCBZ and 3OHCBZ in contact with material taken from a rapid sand filter of a German waterworks. Despite their similar structure, which differs only in the position of the phenolic OH moiety, both compounds underwent distinct transformation reactions leading to the formation of a variety of transformation products (TPs). The main biochemical reactions thereby included enzymatic transformation of 2OHCBZ resulting in the formation of a reactive iminoquinone intermediate (2OHCBZ) and nitration via peroxynitrite (2OHCBZ and 3OHCBZ) as well as formation of radicals leading to dimerization (3OHCBZ). Further transformation reactions included hydroxylation, ring cleavage, loss of carbamoyl group, and decarboxylation, as well as O-methylation.

Refractory organic pollutants and toxicity in pulp and paper mill wastewaters

This review describes medium and high molecular weight organic material found in wastewaters from pulp and paper industry. The aim is to review the versatile pollutants and the analysis methods for their determination. Among other pollutants, biocides, extractives, and lignin-derived compounds are major contributors to harmful effects, such as toxicity, of industrial wastewaters. Toxicity of wastewaters from pulp and paper mills is briefly evaluated including the methods for toxicity analyses. Traditionally, wastewater purification includes mechanical treatment followed by chemical and/or biological treatment processes. A variety of methods are available for the purification of industrial wastewaters, including aerobic and anaerobic processes. However, some fractions of organic material, such as lignin and its derivatives, are difficult to degrade. Therefore, novel chemical methods, including electrochemical and oxidation processes, have been developed for separate use or in combination with biological treatment processes.

Fate and metabolism of tetrabromobisphenol A in soil slurries without and with the amendment with the alkylphenol degrading bacterium Sphingomonas sp. strain TTNP3

Transformation of ring-(14)C-labelled tetrabromobisphenol-A (TBBPA) was studied in an oxic soil slurry with and without amendment with Sphingomonas sp. strain TTNP3, a bacterium degrading bisphenol-A. TBBPA degradation was accompanied by mineralization and formation of metabolites and bound-residues. The biotransformation was stimulated in the slurry bio-augmented with strain TTNP3, via a mechanism of metabolic compensation, although this strain did not grow on TBBPA. In the absence and presence of strain TTNP3, six and nine metabolites, respectively, were identified. The initial O-methylation metabolite (TBBPA-monomethyl ether) and hydroxytribromobisphenol-A were detected only when strain TTNP3 was present. Four primary metabolic pathways of TBBPA in the slurries are proposed: oxidative skeletal rearrangements, O-methylation, ipso-substitution, and reductive debromination. Our study provides for the first time the information about the complex metabolism of TBBPA in oxic soil and suggests that type II ipso-substitution could play a significant role in the fate of alkylphenol derivatives in the environment.

"Rational" management of dichlorophenols biodegradation by the microalga Scenedesmus obliquus

The microalga Scenedesmus obliquus exhibited the ability to biodegrade dichlorophenols (dcps) under specific autotrophic and mixotrophic conditions. According to their biodegradability, the dichlorophenols used can be separated into three distinct groups. Group I (2,4-dcp and 2,6 dcp – no meta-substitution) consisted of quite easily degraded dichlorophenols, since both chloride substituents are in less energetically demanding positions. Group II (2,3-dcp, 2,5-dcp and 3,4-dcp – one meta-chloride) was less susceptible to biodegradation, since one of the two substituents, the meta one, required higher energy for C-Cl-bond cleavage. Group III (3,5-dcp – two meta-chlorides) could not be biodegraded, since both chlorides possessed the most energy demanding positions. In general, when the dcp-toxicity exceeded a certain threshold, the microalga increased the energy offered for biodegradation and decreased the energy invested for biomass production. As a result, the biodegradation per cell volume of group II (higher toxicity) was higher, than group I (lower toxicity) and the biodegradation of dichlorophenols (higher toxicity) was higher than the corresponding monochlorophenols (lower toxicity). The participation of the photosynthetic apparatus and the respiratory mechanism of microalga to biodegrade the group I and the group II, highlighted different bioenergetic strategies for optimal management of the balance between dcp-toxicity, dcp-biodegradability and culture growth. Additionally, we took into consideration the possibility that the intermediates of each dcp-biodegradation pathway could influence differently the whole biodegradation procedures. For this reason, we tested all possible combinations of phenolic intermediates to check cometabolic interactions. The present contribution bring out the possibility of microalgae to operate as “smart” bioenergetic “machines”, that have the ability to continuously “calculate” the energy reserves and “use” the most energetically advantageous dcp-biodegradation strategy. We tried to manipulate the above fact, changing the energy reserves and as a result the chosen strategy, in order to take advantage of their abilities in detoxifying the environment.

Fate of triclosan in field soils receiving sewage sludge

The anti-microbial substance triclosan can partition to sewage sludge during wastewater treatment and subsequently transfer to soil when applied to land. Here, we describe the fate of triclosan in a one-year plot experiment on three different soils receiving sludge. Triclosan and methyl-triclosan concentrations were measured in soil samples collected monthly from three depths. A large fraction of triclosan loss appeared to be explained by transformation to methyl-triclosan. After 12 months less than 20% of the initial triclosan was recovered from each soil. However, the majority was recovered as methyl-triclosan. Most of the chemical recovered at the end of the experiment (both triclosan and methyl-triclosan) was still in the top 10 cm layer, although there was translocation to lower soil horizons in all three soils. Between 16.5 and 50.6% of the applied triclosan was unaccounted for after 12 months either as a consequence of degradation or the formation of non-extractable residues.

Microbially mediated O-methylation of bisphenol A results in metabolites with increased toxicity to the developing zebrafish (Danio rerio) embryo

Bisphenol A (BPA) is used in the manufacture of plastics, and has been identified in various environmental matrices, including human serum and breast milk. The prevalence of BPA in the environment and the potential exposure to humans underscores the need to more fully understand the fate of BPA in the environment and the resulting effects and toxicity to humans and other organisms. Here we demonstrate that Mycobacterium species, including Mycobacterium vanbaalenii strain PYR-1, are able to O-methylate BPA to its mono- and dimethyl ether derivatives (BPA MME and BPA DME, respectively). The O-methylation of BPA results in metabolites with increased toxicity as shown from differences in survival and occurrence of developmental lesions in developing zebrafish embryos exposed to BPA, BPA MME, and BPA DME. The mono- and dimethyl ether derivatives were more toxic than BPA, resulting in increased mortality at 5 (LC(50) = 0.66 and 1.2 mg L(-1)) and 28 (LC(50) = 0.38, <0.5 mg L(-1)) days post fertilization. Furthermore, exposure to either of the O-methylated metabolites resulted in an increase in the incidence of developmental lesions as compared to BPA exposure. These data illustrate a new mechanism for microbial transformation of BPA, producing metabolites warranting further study to understand their prevalence and effects in the environment.

Biodegradation of triclosan and formation of methyl-triclosan in activated sludge under aerobic conditions

Triclosan is an antimicrobial agent which is widely used in household and personal care products. Widespread use of this compound has led to the elevated concentrations of triclosan in wastewater, wastewater treatment plants (WWTPs) and receiving waters. Removal of triclosan and formation of triclosan-methyl was investigated in activated sludge from a standard activated sludge WWTP equipped with enhanced biological phosphorus removal. The removal was found to occur mainly under aerobic conditions while under anoxic (nitrate reducing) and anaerobic conditions rather low removal rates were determined. In a laboratory-scale activated sludge reactor 75% of the triclosan was removed under aerobic conditions within 150 h, while no removal was observed under anaerobic or anoxic conditions. One percent of the triclosan was converted to triclosan-methyl under aerobic conditions, less under anoxic (nitrate reducing) and none under anaerobic conditions.

The microbiota of an unpolluted calcareous soil faces up chlorophenols: Evidences of resistant strains with potential for bioremediation

To highlight the effects of a variety of chlorophenols (CP) in relation to the response of an indigenous bacterial community, an agricultural Mediterranean calcareous soil has been studied in microcosms incubated under controlled laboratory conditions. Soil samples were artificially polluted with 2-monochlorophenol (MCP), 2,4,6-trichlorophenol (TCP) and pentachlorophenol (PCP), at concentrations ranging from 0.1 up to 5000 mg kg(-1). Both activity and composition of the microbial community were assessed during several weeks, respectively, by respirometric methods and PCR-DGGE analysis of extracted DNA and RNA. Significant decreases in soil respirometric values and changes in the bacterial community composition were observed at concentrations above 1000 mg kg(-1) MCP and TCP, and above 100 mg kg(-1) PCP. However, the persistence of several active bacterial populations in soil microcosms contaminated with high concentration of CP, as indicated by DGGE fingerprints, suggested the capacity of these native bacteria to survive in the presence of the pollutants, even without a previous adaptation or contact with them. The isolation of potential CP degraders was attempted by culture plating from microcosms incubated with high CP concentrations. Twenty-three different isolates were screened for their resistance to TCP and PCP. The most resistant isolates were identified as Kocuria palustris, Lysobacter gummosus, Bacillus sp. and Pseudomonas putida, according to 16S rRNA gene homology. In addition, these four isolates also showed the capacity to reduce the concentration of TCP and PCP from 15% to 30% after 5d of incubation in laboratory assays (initial pollutant concentration of 50 mg L(-1)). Isolate ITP29, which could be a novel species of Bacillus, has been revealed as the first known member in this bacterial group with potential for CP bioremediation applications, usually wide-spread in the soil natural communities, which has not been reported to date as a CP degrader.

Biodegradation potential of the genus Rhodococcus

A large number of aromatic compounds and organic nitriles, the two groups of compounds covered in this review, are intermediates, products, by-products or waste products of the chemical and pharmaceutical industries, agriculture and the processing of fossil fuels. The majority of these synthetic substances (xenobiotics) are toxic and their release and accumulation in the environment pose a serious threat to living organisms. Bioremediation using various bacterial strains of the genus Rhodococcus has proved to be a promising option for the clean-up of polluted sites. The large genomes of rhodococci, their redundant and versatile catabolic pathways, their ability to uptake and metabolize hydrophobic compounds, to form biofilms, to persist in adverse conditions and the availability of recently developed tools for genetic engineering in rhodococci make them suitable industrial microorganisms for biotransformations and the biodegradation of many organic compounds. The peripheral and central catabolic pathways in rhodococci are characterized for each type of aromatics (hydrocarbons, phenols, halogenated, nitroaromatic, and heterocyclic compounds) in this review. Pathways involved in the hydrolysis of nitrile pollutants (aliphatic nitriles, benzonitrile analogues) and the corresponding enzymes (nitrilase, nitrile hydratase) are described in detail. Examples of regulatory mechanisms for the expression of the catabolic genes are given. The strains that efficiently degrade the compounds in question are highlighted and examples of their use in biodegradation processes are presented.

Investigation of the biotransformation of pentachlorophenol and pulp paper mill effluent decolorisation by the bacterial strains in a mixed culture

Mixed culture of two bacterial strains Bacillus sp. and Serratia marcescens showed potential pentachlorophenol (PCP) degradation and decolorisation of pulp paper mill effluent. The physico-chemical quality of pulp paper mill effluent has been analyzed after 168 h incubation period degraded by mixed culture. The study revealed that it has decreased high load of BOD, COD, TS, TDS, TSS, sulphate, phosphate, total nitrogen, total phenols, metals and different salts (i.e. chloride, sodium, nitrate, potassium) at 168 h incubation period. PCP degradation in pulp paper mill effluent was confirmed by HPLC analysis. Mixed culture was found to degrade PCP up to (94%) present in pulp paper mill effluent with 1% glucose and 0.5% peptone (w/v) at 30+/-1 degrees C, pH 8.0+/-0.2 at 120 rpm in 168 h incubation period. The simultaneous release of chloride ion up to 1,200 mg/l at 168 h emphasized the bacterial dechlorination in the medium. The pulp paper mill effluent degradation was also supported by decline in pH, AOX (absorbable organic halides), color, D.O., BOD, COD and PCP. The analysis of pulp paper mill effluent degradation products by GC-MS analysis revealed the formation of low molecular weight compound like 2-chlorophenol (RT=3.8 min) and tetrachlorohydroquinone (RT=11.86 min) from PCP extracted degraded sample. Further, mixed culture may be used for bioremediation of PCP containing pulp paper mill waste in the environment.

Microbial O-methylation of the flame retardant tetrabromobisphenol-A

We demonstrated the O-methylation of tetrabromobisphenol-A (TBBPA) [4,4'-isopropylidenebis (2,6-dibromophenol)] to its mono- and dimethyl ether derivatives by microorganisms present in different sediments. A most probable number assay of a marsh sediment suggested that up to 10% of the total aerobic heterotrophs may be capable of O-methylation. Although TBBPA dimethyl ether is not produced in industry, it has been detected in terrestrial and aquatic sediments. Our study supports the hypothesis that TBBPA dimethyl ether is a product of microbial O-methylation. The O-methylation of TBBPA, as well as its analog, tetrachlorobisphenol-A (TCBPA), was also demonstrated in cultures of two chlorophenol-metabolizing bacteria, Mycobacterium fortuitum CG-2 and Mycobacterium chlorophenolicum PCP-1. These strains also mediated the O-methylation of 2,6-dibromophenol and 2,6-dichlorophenol, analogs of TBBPA and TCBPA, to their corresponding anisoles, but 2,6-fluorophenol was not transformed. Due to the addition of hydrophobic methyl groups, O-methylated derivatives are more lipophilic, increasing the probability of bioaccumulation in the food chain. Future research regarding the toxicological effects of the O-methylated derivatives of TBBPA is recommended and will further elucidate potential risks to environmental and human health.

Genomic analysis of polycyclic aromatic hydrocarbon degradation in Mycobacterium vanbaalenii PYR-1

Mycobacterium vanbaalenii PYR-1 is well known for its ability to degrade a wide range of high-molecular-weight (HMW) polycyclic aromatic hydrocarbons (PAHs). The genome of this bacterium has recently been sequenced, allowing us to gain insights into the molecular basis for the degradation of PAHs. The 6.5 Mb genome of PYR-1 contains 194 chromosomally encoded genes likely associated with degradation of aromatic compounds. The most distinctive feature of the genome is the presence of a 150 kb major catabolic region at positions 494 approximately 643 kb (region A), with an additional 31 kb region at positions 4,711 approximately 4,741 kb (region B), which is predicted to encode most enzymes for the degradation of PAHs. Region A has an atypical mosaic structure made of several gene clusters in which the genes for PAH degradation are complexly arranged and scattered around the clusters. Significant differences in the gene structure and organization as compared to other well-known aromatic hydrocarbon degraders including Pseudomonas and Burkholderia were revealed. Many identified genes were enriched with multiple paralogs showing a remarkable range of diversity, which could contribute to the wide variety of PAHs degraded by M. vanbaalenii PYR-1. The PYR-1 genome also revealed the presence of 28 genes involved in the TCA cycle. Based on the results, we proposed a pathway in which HMW PAHs are degraded into the beta-ketoadipate pathway through protocatechuate and then mineralized to CO2 via TCA cycle. We also identified 67 and 23 genes involved in PAH degradation and TCA cycle pathways, respectively, to be expressed as proteins.

Cloning of a gene cluster involved in the catabolism of p-nitrophenol by Arthrobacter sp. strain JS443 and characterization of the p-nitrophenol monooxygenase

The npd gene cluster, which encodes the enzymes of a p-nitrophenol catabolic pathway from Arthrobacter sp. strain JS443, was cloned and sequenced. Three genes, npdB, npdA1, and npdA2, were independently expressed in Escherichia coli in order to confirm the identities of their gene products. NpdA2 is a p-nitrophenol monooxygenase belonging to the two-component flavin-diffusible monooxygenase family of reduced flavin-dependent monooxygenases. NpdA1 is an NADH-dependent flavin reductase, and NpdB is a hydroxyquinol 1,2-dioxygenase. The npd gene cluster also includes a putative maleylacetate reductase gene, npdC. In an in vitro assay containing NpdA2, an E. coli lysate transforms p-nitrophenol stoichiometrically to hydroquinone and hydroxyquinol. It was concluded that the p-nitrophenol catabolic pathway in JS443 most likely begins with a two-step transformation of p-nitrophenol to hydroxy-1,4-benzoquinone, catalyzed by NpdA2. Hydroxy-1,4-benzoquinone is reduced to hydroxyquinol, which is degraded through the hydroxyquinol ortho cleavage pathway. The hydroquinone detected in vitro is a dead-end product most likely resulting from chemical or enzymatic reduction of the hypothetical intermediate 1,4-benzoquinone. NpdA2 hydroxylates a broad range of chloro- and nitro-substituted phenols, resorcinols, and catechols. Only p-nitro- or p-chloro-substituted phenols are hydroxylated twice. Other substrates are hydroxylated once, always at a position para to a hydroxyl group.

The recent evolution of pentachlorophenol (PCP)-4-monooxygenase (PcpB) and associated pathways for bacterial degradation of PCP

Man-made polychlorinated phenols such as pentachlorophenol (PCP) have been used extensively since the 1920s as preservatives to prevent fungal attack on wood. During this time, they have become serious environmental contaminants. Despite the recent introduction of PCP in the environment on an evolutionary time scale, PCP-degrading bacteria are present in soils worldwide. The initial enzyme in the PCP catabolic pathway of numerous sphingomonads, PCP-4-monooxygenase (PcpB), catalyzes the para-hydroxylation of PCP to tetrachlorohydroquinone and is encoded by the pcpB gene. This review examines the literature concerning pcpB and supports the suggestion that pcpB/PcpB should be considered a model system for the study of recent evolution of catabolic pathways among bacteria that degrade xenobiotic molecules introduced into the environment during the recent past.

Lindane removal induction byStreptomyces sp. M7

Gamma-hexachlorocyclohexane (gamma-HCH or lindane), one of the most commonly used pesticides, has been mainly used in agriculture; this pesticide is known to be highly toxic and persistent, causing serious water and soil contamination. The objective of the present work is to study the effect of low glucose concentration and the addition of lindane at different growing time on the pesticide detoxification ability of Streptomyces M7. After 96 h of incubation in synthetic medium containing glucose 0.6 g l(-1) with the addition of lindane 100 microg l(-1) at 20 h of incubation, a typical diauxic curve was obtained: glucose was the preferred substrate until 24 h, at 48 h, when the carbohydrate was depleted, the microorganism consumed the pesticide like carbon source. On the other hand, lindane removal induction was observed, which was greater when the pesticide was added to the medium at 20 h than 6 h of incubation. Between 72 and 96 h, a maximum of approximately 86% of the Cl(-) was released when lindane was added to the medium at 20 h, whereas approximately 70% and 67% Cl(-) was released in the medium when the pesticide was added at 0 and 6 h of incubation respectively. This is the first report of chloride release from inoculated medium supplemented with lindane, suggesting that the pesticide was degraded by Streptomyces sp. under aerobic conditions.

Hydroxyquinol pathway for microbial degradation of halogenated aromatic compounds

Several peripheral metabolic pathways can be used by microorganisms to degrade toxic aromatic compounds that are known to pollute the environment. Hydroxyquinol (1,2,4-trihydroxybenzene) is one of the central intermediates in the degradative pathway of a large variety of aromatic compounds. The present review describes the microorganisms involved in the degradative pathway, the key enzymes involved in the formation and splitting of the aromatic ring of (chloro)hydroxyquinol as well as the central intermediates formed. An attempt was also made to provide some estimation for genetic basis of the hydroxyquinol pathway.

Identification and molecular characterization of a Bacillus subtilis IS13 strain involved in the biodegradation of 4,5,6-trichloroguaiacol

4,5,6-Trichloroguaiacol (4,5,6-TCG) is a recalcitrant organochlorine compound produced during pulp bleaching and a potential environmental hazard in paper mill effluents. We report here the identification by biochemical tests and molecular biological analysis, using 16S ribotyping, of a 4,5,6-TCG-degrading bacterium, identified as a strain of Bacillus subtilis that is most closely related according to the phylogenetic analysis to B. subtilis strain Lactipan (alignment score 99%). Biodegradation of 4,5,6-TCG by this organism in a mineral salts medium was shown to occur only when the inoculum was composed of cells in the stationary phase of growth and to be accelerated by an additional carbon source, such as glucose, sucrose, glycerol or molasses. An additional nitrogen source (as ammonium sulfate) did not affect the rate of 4,5,6-TGC removal. No plasmids were detected in the bacterial cells. This is the first strain of B. subtilis which degrades chlorophenols and shows that 4,5,6-TCG is not degraded by cometabolism and that the gene encoding this characteristic is probably located on the chromosome. The lack of requirement for additional nitrogen source, the ability to enhance biodegradation by adding cheap carbon sources such as molasses, and the fact the trait is likely to be stable since it is encoded on the cell chromosome, are all characteristics that make the organism an attractive possibility for treatment of wastes and environments polluted with organochlorine compounds.

Characterization of tetrachlorohydroquinone reductive dehalogenase from Sphingomonas sp. UG30

Tetrachlorohydroquinone reductive dehalogenase (PcpC) is the second of three enzymes that catalyze the initial degradation of pentachlorophenol in Sphingomonas sp. UG30 and several other bacterial strains. The UG30 PcpC shares a high degree (94%) of primary sequence identity with the well-studied PcpC from Sphingobium chlorophenolicum ATCC 39723. Significant differences, however, were observed between the two PcpC enzymes in some of their functional and kinetic properties. The temperature optimum of the UG30 PcpC is 10 degrees C higher and the pH optimum is approximately 2 units higher than the S. chlorophenolicum PcpC. In addition, the S. chlorophenolicum PcpC is subject to inhibition by the substrate tetrachlorohydroquinone (TCHQ), and this has necessitated the use of a mutant enzyme, which was not inhibited by TCHQ, for kinetic studies. In contrast, the UG30 PcpC was not inhibited by TCHQ and this may allow detailed kinetic and mechanistic studies using the wild-type enzyme.

Evidence for natural horizontal transfer of the pcpB gene in the evolution of polychlorophenol-degrading sphingomonads

The chlorophenol degradation pathway in Sphingobium chlorophenolicum is initiated by the pcpB gene product, pentachlorophenol-4-monooxygenase. The distribution of the gene was studied in a phylogenetically diverse group of polychlorophenol-degrading bacteria isolated from contaminated groundwater in Kärkölä, Finland. All the sphingomonads isolated were shown to share pcpB gene homologs with 98.9 to 100% sequence identity. The gene product was expressed when the strains were induced by 2,3,4,6-tetrachlorophenol. A comparative analysis of the 16S rDNA and pcpB gene trees suggested that a recent horizontal transfer of the pcpB gene was involved in the evolution of the catabolic pathway in the Kärkölä sphingomonads. The full-length Kärkölä pcpB gene allele had approximately 70% identity with the three pcpB genes previously sequenced from sphingomonads. It was very closely related to the environmental clones obtained from chlorophenol-enriched soil samples (M. Beaulieu, V. Becaert, L. Deschenes, and R. Villemur, Microbiol. Ecol. 40:345-355, 2000). The gene was not present in polychlorophenol-degrading nonsphingomonads isolated from the Kärkölä source.

Changing the substrate reactivity of 2-hydroxybiphenyl 3-monooxygenase from Pseudomonas azelaica HBP1 by directed evolution

The substrate reactivity of the flavoenzyme 2-hydroxybiphenyl 3-monooxygenase (EC, HbpA) was changed by directed evolution using error-prone PCR. In situ screening of mutant libraries resulted in the identification of proteins with increased activity towards 2-tert-butylphenol and guaiacol (2-methoxyphenol). One enzyme variant contained amino acid substitutions V368A/L417F, which were inserted by two rounds of mutagenesis. The double replacement improved the efficiency of substrate hydroxylation by reducing the uncoupled oxidation of NADH. With guaiacol as substrate, the two substitutions increased V(max) from 0.22 to 0.43 units mg(-1) protein and decreased the K'(m) from 588 to 143 microm, improving k'(cat)/K'(m) by a factor of 8.2. With 2-tert-butylphenol as the substrate, k'(cat) was increased more than 5-fold. Another selected enzyme variant contained amino acid substitution I244V and had a 30% higher specific activity with 2-sec-butylphenol, guaiacol, and the "natural" substrate 2-hydroxybiphenyl. The K'(m) for guaiacol decreased with this mutant, but the K'(m) for 2-hydroxybiphenyl increased. The primary structure of HbpA shares 20.1% sequence identity with phenol 2-monooxygenase from Trichosporon cutaneum. Structure homology modeling with this three-domain enzyme suggests that Ile(244) of HbpA is located in the substrate binding pocket and is involved in accommodating the phenyl substituent of the phenol. In contrast, Val(368) and Leu(417) are not close to the active site and would not have been obvious candidates for modification by rational design.

Evolution of a metabolic pathway for degradation of a toxic xenobiotic: the patchwork approach

The pathway for degradation of the xenobiotic pesticide pentachlorophenol in Sphingomonas chlorophenolica probably evolved in the past few decades by the recruitment of enzymes from two other catabolic pathways. The first and third enzymes in the pathway, pentachlorophenol hydroxylase and 2,6-dichlorohydroquinone dioxygenase, may have originated from enzymes in a pathway for degradation of a naturally occurring chlorinated phenol. The second enzyme, a reductive dehalogenase, may have evolved from a maleylacetoacetate isomerase normally involved in degradation of tyrosine. This apparently recently assembled pathway does not function very well: pentachlorophenol hydroxylase is quite slow, and tetrachlorohydroquinone dehalogenase is subject to severe substrate inhibition.

High biodegradation levels of 4,5,6-trichloroguaiacol by Bacillus sp. isolated from cellulose pulp mill effluent

An aerobic Gram positive spore-forming bacterium was isolated from cellulose pulp mill effluent. This microorganism, identified as Bacillus sp. and named IS13, was able to rapidly degrade the organic chlorinated compound 4,5,6-trichloroguaiacol (4,5,6-TCG) from a culture containing 50 mg/l, which corresponds to about 3x104 times the concentration found in the original effluent. The biodegradation of this compound, usually found in cellulose pulp mill effluents, was evaluated by spectrophotometry and gas chromatography analysis. During 4,5,6-TCG decreasing, the lack of by-products had shown by such analysis lead to verify the possibility of either adsorption or absorption of 4,5,6-TCG by the cells, instead of real biodegradation. There were no traces of 4,5,6-TCG after lysozyme and SDS cell disruption. Vigorous extraction was applied before spectrophotometry analysis and there was no release of residual 4,5,6-TCG. Plasmid isolation was attempted by using different protocols. The best results were reached by CTAB method, but no plasmid DNA was found in Bacillus sp. IS13. The results suggest that genes located at the bacterial chromosome might mediate the high decrease of 4,5,6-TCG. The importance of this work is that, in being a natural ocurring microorganism, Bacillus sp. IS13, can be used as inoculum in plant effluents to best organochlorinated compounds biodegradation.

Morpholine degradation pathway of Mycobacterium aurum MO1: direct evidence of intermediates by in situ 1H nuclear magnetic resonance

Resting Mycobacterium aurum MO1 cells were incubated with morpholine, a waste from the chemical industry. The kinetics of biodegradation was monitored by using in situ nuclear magnetic resonance (NMR). The incubation medium was directly analyzed by 1H NMR. This technique allowed the unambiguous identification of two intermediates of the metabolic pathway involved in the biodegradation process, glycolate and 2-(2-aminoethoxy)acetate. The latter compound, which was not commercially available, was synthesized, in three steps, from 2-(2-aminoethoxy)ethanol. Quantitative analysis of the kinetics of degradation of morpholine was performed by integrating the signals of the different metabolites in 1H-NMR spectra. Morpholine was degraded within 10 h. The intermediates increased during the first 10 h and finally disappeared after 20 h incubation. Assays of degradation were also carried out with glycolate and ethanolamine, hypothetical intermediates of the morpholine degradation pathway. They were degraded within 4 and 8 h, respectively. Until now, no tool for direct detection of intermediates or even morpholine has been available, consequently, only hypothetical pathways have been proposed. The approach described here gives both qualitative and quantitative information about the metabolic routes used in morpholine degradation by M. aurum MO1. It could be used to investigate many biodegradative processes.

Biodegradation of groundwater pollutants by a combined culture of Mycobacterium vaccae and a Rhodococcus sp

The catabolism of selected groundwater pollutants by a combined culture of Mycobacterium vaccae and a Rhodococcus sp. (strain R-22) was investigated. The M. vaccae-R-22 combined culture was five times more effective in mineralizing benzene than either organism alone. Mycobacterium vaccae oxidized benzene to phenol, and R-22 catabolized the phenol to cellular components and CO2. Benzene did not support growth of M. vaccae, R-22, or the combined culture. Optimization of ratios of the two species indicated that the maximum mineralization of benzene occurred at an initial ratio of 75% M. vaccae to 25% R-22. Cell fractionation of the combined culture after mineralization of [U-14C]benzene indicated that 10% of the benzene carbon was incorporated into cell material, and of this 45% was present in protein and 20% in nucleic acids. This suggested that minimally one species could utilize the products of benzene as a nutrient source. The M. vaccae-R-22 combined culture catabolized ethylbenzene and chlorobenzene without the accumulation of phenolic intermediates, which are inhibitory to M. vaccae's ability to degrade the parent compounds. This study demonstrates that defined mixed cultures may be useful in studying the effects of environmental pollutant degradation on microbial ecosystems and mineralization of these pollutants by the ecosystem.

In vivo levels of chlorinated hydroquinones in a pentachlorophenol-degrading bacterium

Sphingomonas chlorophenolica RA-2 is a soil microorganism that can grow on pentachlorophenol (PCP) as a sole carbon source. In this microorganism, PCP is converted to tetrachlorohydroquinone (TCHQ), trichlorohydroquinone, and 2,6-dichlorohydroquinone. The remainder of the pathway has not yet been defined. The ability to grow on PCP as a sole carbon source is remarkable because of the toxicity of PCP and its chlorinated hydroquinone metabolites. Experiments in which the levels of PCP and chlorinated hydroquinones were measured in cells metabolizing [U-14C]PCP revealed that the levels of chlorinated hydroquinones in the cytoplasm are in the low micromolar range. The toxicity of chlorinated hydroquinones was evaluated by exposure of Escherichia coli cells that had been treated with EDTA (to remove the outer membrane) to TCHQ. Significant toxicity due to TCHQ was not apparent until concentrations of 500 microM and higher. Thus, an important part of the explanation for why S. chlorophenolica RA-2 is able to grow on PCP as a sole carbon source is undoubtedly that it can process sufficient carbon for growth without accumulating high levels of toxic intermediates.

Straw compost and bioremediated soil as inocula for the bioremediation of chlorophenol-contaminated soil

We evaluated the use of straw compost and remediated soil as inocula for bioremediation of chlorophenol-contaminated soil. The in situ biotransformation of pentachlorophenol (PCP) and mineralization of radiolabeled [U-(sup14)C]PCP by straw compost and remediated soil were studied under field-simulating conditions before and after 3 months of adaptation with PCP in a percolator. After PCP adaptation, the straw compost mineralized up to 56% of the [(sup14)C]PCP. No partial dechlorination of PCP was found. The native straw compost did not mineralize PCP, but partial dechlorination of PCP occurred (i) at pH 8 under near-thermophilic conditions (45(deg)C) and (ii) at pH 7 under aerobic and mesophilic conditions. No biotransformation reactions occurred at room temperature (25(deg)C) at pH 8. Enrichment in the percolator enhanced the mineralization rate of remediated soil to 56% compared with that of the native remediated soil, which mineralized 24% of [(sup14)C]PCP added. Trace amounts of chloroanisoles as the only biotransformation products were detected in PCP-adapted remediated soil. Both inoculants studied here showed effective mineralization of PCP when they were adapted to PCP in the percolator. No harmful side reactions, such as extensive methylation, were observed.