Crystal structure of 3-chlorocatechol 1,2-dioxygenase key enzyme of a new modified ortho-pathway from the Gram-positive Rhodococcus opacus 1CP grown on 2-chlorophenol

Protein3D: Enabling analysis and extraction of metal-containing sites from the Protein Data Bank with molSimplify

Metalloenzymes catalyze a wide range of chemical transformations, with the active site residues playing a key role in modulating chemical reactivity and selectivity. Unlike smaller synthetic catalysts, a metalloenzyme active site is embedded in a larger protein, which makes interrogation of electronic properties and geometric features with quantum mechanical calculations challenging. Here we implement the ability to fetch crystallographic structures from the Protein Data Bank and analyze the metal binding sites in the program molSimplify. We show the usefulness of the newly created protein3D class to extract the local environment around non-heme iron enzymes containing a two histidine motif and prepare 372 structures for quantum mechanical calculations. Our implementation of protein3D serves to expand the range of systems molSimplify can be used to analyze and will enable high-throughput study of metal-containing active sites in proteins.

Intradiol ring cleavage dioxygenases from herbivorous spider mites as a new detoxification enzyme family in animals

Background

Generalist herbivores such as the two-spotted spider mite Tetranychus urticae thrive on a wide variety of plants and can rapidly adapt to novel hosts. What traits enable polyphagous herbivores to cope with the diversity of secondary metabolites in their variable plant diet is unclear. Genome sequencing of T. urticae revealed the presence of 17 genes that code for secreted proteins with strong homology to “intradiol ring cleavage dioxygenases (DOGs)” from bacteria and fungi, and phylogenetic analyses show that they have been acquired by horizontal gene transfer from fungi. In bacteria and fungi, DOGs have been well characterized and cleave aromatic rings in catecholic compounds between adjacent hydroxyl groups. Such compounds are found in high amounts in solanaceous plants like tomato, where they protect against herbivory. To better understand the role of this gene family in spider mites, we used a multi-disciplinary approach to functionally characterize the various T. urticae DOG genes.

Results

We confirmed that DOG genes were present in the T. urticae genome and performed a phylogenetic reconstruction using transcriptomic and genomic data to advance our understanding of the evolutionary history of spider mite DOG genes. We found that DOG expression differed between mites from different plant hosts and was induced in response to jasmonic acid defense signaling. In consonance with a presumed role in detoxification, expression was localized in the mite’s gut region. Silencing selected DOGs expression by dsRNA injection reduced the mites’ survival rate on tomato, further supporting a role in mitigating the plant defense response. Recombinant purified DOGs displayed a broad substrate promiscuity, cleaving a surprisingly wide array of aromatic plant metabolites, greatly exceeding the metabolic capacity of previously characterized microbial DOGs.

Conclusion

Our findings suggest that the laterally acquired spider mite DOGs function as detoxification enzymes in the gut, disarming plant metabolites before they reach toxic levels. We provide experimental evidence to support the hypothesis that this proliferated gene family in T. urticae is causally linked to its ability to feed on an extremely wide range of host plants.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01323-1.

Optimization and reconstruction of two new complete degradation pathways for 3-chlorocatechol and 4-chlorocatechol in Escherichia coli

Chlorinated aromatic compounds are a serious environmental concern because of their widespread occurrence throughout the environment. Although several microorganisms have evolved to gain the ability to degrade chlorinated aromatic compounds and use them as carbon sources, they still cannot meet the diverse needs of pollution remediation. In this study, the degradation pathways for 3-chlorocatechol (3CC) and 4-chlorocatechol (4CC) were successfully reconstructed by the optimization, synthesis, and assembly of functional genes from different strains. The addition of a ¹³C-labeled substrate and functional analysis of different metabolic modules confirmed that the genetically engineered strains can metabolize chlorocatechol similar to naturally degrading strains. The strain containing either of these artificial pathways can degrade catechol, 3CC, and 4CC completely, although differences in the degradation efficiency may be noted. Proteomic analysis and scanning electron microscopy observation showed that 3CC and 4CC have toxic effects on Escherichia coli, but the engineered bacteria can significantly eliminate these inhibitory effects. As core metabolic pathways for the degradation of chloroaromatics, the two chlorocatechol degradation pathways constructed in this study can be used to construct pollution remediation-engineered bacteria, and the related technologies may be applied to construct complete degradation pathways for complex organic hazardous materials.

Biological Inspirations: Iron Complexes Mimicking the Catechol Dioxygenases

Within the broad group of Fe non-heme oxidases, our attention was focused on the catechol 1,2- and 2,3-dioxygenases, which catalyze the oxidative cleavage of aromatic rings. A large group of Fe complexes with N/O ligands, ranging from N₃ to N₂O₂S, was developed to mimic the activity of these enzymes. The Fe complexes discussed in this work can mimic the intradiol/extradiol catechol dioxygenase reaction mechanism. Electronic effects of the substituents in the ligand affect the Lewis acidity of the Fe center, increasing the ability to activate dioxygen and enhancing the catalytic activity of the discussed biomimetic complexes. The ligand architecture, the geometric isomers of the complexes, and the substituent steric effects significantly affect the ability to bind the substrate in a monodentate and bidentate manner. The substrate binding mode determines the preferred mechanism and, consequently, the main conversion products. The preferred mechanism of action can also be affected by the solvents and their ability to form the stable complexes with the Fe center. The electrostatic interactions of micellar media, similar to SDS, also control the intradiol/extradiol mechanisms of the catechol conversion by discussed biomimetics.

Challenges and opportunities for the biodegradation of chlorophenols: Aerobic, anaerobic and bioelectrochemical processes

Chlorophenols (CPs) are highly toxic and refractory contaminants which widely exist in various environments and cause serious harm to human and environment health and safety. This review provides comprehensive information on typical CPs biodegradation technologies, the most green and benign ones for CPs removal. The known aerobic and anaerobic degradative bacteria, functional enzymes, and metabolic pathways of CPs as well as several improving methods and critical parameters affecting the overall degradation efficiency are systematically summarized and clarified. The challenges for CPs mineralization are also discussed, mainly including the dechlorination of polychlorophenols (poly-CPs) under aerobic condition and the ring-cleavage of monochlorophenols (MCPs) under anaerobic condition. The coupling of functional materials and degraders as well as the operation of sequential anaerobic-aerobic bioreactors and bioelectrochemical system (BES) are promising strategies to overcome some current limitations. Future perspective and research gaps in this field are also proposed, including the further understanding of microbial information and the specific role of materials in CPs biodegradation, the potential application of innovative biotechnologies and new operating modes to optimize and maximize the function of the system, and the scale-up of bioreactors towards the efficient biodegradation of CPs.

Coupling the phenolic oxidation capacities of a bacterial consortium and in situ-generated manganese oxides in a moving bed biofilm reactor (MBBR)

Phenolic wastewater containing phenol and 4-chlorophenol pose a risk to the environment and to human health. Treating them using chemical-biological coupling method is challenging. In this study, manganese oxidizing bacteria (MnOB) were enriched in moving bed biofilm reactor (MBBR) using synthetic phenol wastewater (800 mg L^-1) to facilitate in situ production of biogenic manganese oxides (BioMnOx) after 90 days of operation. Then, 4-chlorophenol (4-CP) was added to the MBBR to simulate mixed phenolic wastewater. Comparing the MBBR (R1) without feeding Mn(II) and the MBBR with BioMnOx (R2) production, R2 exhibited robust phenol and 4-CP removal performance. 16S rRNA gene sequencing was employed to determine the microbial community. Subsequently, a batch experiment demonstrated that partly purified BioMnOx does not exhibits a capacity for phenol removal, but can efficiently remove 4-CP. Interestingly, 5-chloro-2-hydroxymuconic semialdehyde was found in the products of 4-CP degradation, which was the unique product of 4-CP degradation by catechol 2,3-dioxygenase (C23O). In both reactors, only catechol 1,2-dioxygenase (C12O) activity from microbes can be detected, indicating that the existence of BioMnOx provide an alternative pathway in addition to microbe driven 4-CP degradation. Overall, MBBR based MnOB enrichment under high phenol concentration was achieved, and 4-CP/phenol removal can be accelerated by in situ-formed BioMnOx. Considering the C23O-like activity of BioMnOx, our results suggest a new coupling strategy that involves nanomaterials and a microbial consortium.

Structural and functional characterization of an intradiol ring-cleavage dioxygenase from the polyphagous spider mite herbivore Tetranychus urticae Koch

Genome analyses of the polyphagous spider mite herbivore Tetranychus urticae (two-spotted spider mite) revealed the presence of a set of 17 genes that code for secreted proteins belonging to the "intradiol dioxygenase-like" subgroup. Phylogenetic analyses indicate that this novel enzyme family has been acquired by horizontal gene transfer. In order to better understand the role of these proteins in T. urticae, we have structurally and functionally characterized one paralog (tetur07g02040). It was demonstrated that this protein is indeed an intradiol ring-cleavage dioxygenase, as the enzyme is able to cleave catechol between two hydroxyl-groups using atmospheric dioxygen. The enzyme was characterized functionally and structurally. The active site of the T. urticae enzyme contains an Fe³⁺ cofactor that is coordinated by two histidine and two tyrosine residues, an arrangement that is similar to those observed in bacterial homologs. However, the active site is significantly more solvent exposed than in bacterial proteins. Moreover, the mite enzyme is monomeric, while almost all structurally characterized bacterial homologs form oligomeric assemblies. Tetur07g02040 is not only the first spider mite dioxygenase that has been characterized at the molecular level, but is also the first structurally characterized intradiol ring-cleavage dioxygenase originating from a eukaryote.

Crystal structure of hydroxyquinol 1,2-dioxygenase PnpC from Pseudomonas putida DLL-E4 and its role of N-terminal domain for catalysis

Hydroxyquinol 1,2-dioxygenase is a key enzyme in the hydroxyquinol pathway of p-nitrophenol (PNP) degradation, and catalyzes the ring cleavage of benzenetriol to maleylacetate. Here, we report the first structure of a hydroxyquinol 1,2-dioxygenase from the Gram-negative bacterium Pseudomonas putida DLL-E4 (PnpC) at the resolution of 2.1 Å. The tertiary structure of PnpC resembles that of the homologous intradiol dioxygenases. The catalytic Fe(III) is pentacoordinated by the conserved Tyr160, Tyr194, His218 and His220, the citrate anion and one water molecule. Among the residues expected to interact with the substrate, structural comparison with the (chloro)catechol dioxygenases suggested that Asp80, Thr81 and Val248 are responsible for the substrate specificity. Moreover, truncation of the N-terminal α-helix of PnpC suggested the N-terminal domain is required for its soluble expression and enzyme catalysis. Our results might provide insights in the substrate recognition and rational design of this enzyme class to be used in bioremediation.

Overcoming antibiotic resistance: Is siderophore Trojan horse conjugation an answer to evolving resistance in microbial pathogens?

Comparative study of siderophore biosynthesis pathway in pathogens provides potential targets for antibiotics and host drug delivery as a part of computationally feasible microbial therapy. Iron acquisition using siderophore models is an essential and well established model in all microorganisms and microbial infections a known to cause great havoc to both plant and animal. Rapid development of antibiotic resistance in bacterial as well as fungal pathogens has drawn us at a verge where one has to get rid of the traditional way of obstructing pathogen using single or multiple antibiotic/chemical inhibitors or drugs. 'Trojan horse' strategy is an answer to this imperative call where antibiotic are by far sneaked into the pathogenic cell via the siderophore receptors at cell and outer membrane. This antibiotic once gets inside, generates a 'black hole' scenario within the opportunistic pathogens via iron scarcity. For pathogens whose siderophore are not compatible to smuggle drug due to their complex conformation and stiff valence bonds, there is another approach. By means of the siderophore biosynthesis pathways, potential targets for inhibition of these siderophores in pathogenic bacteria could be achieved and thus control pathogenic virulence. Method to design artificial exogenous siderophores for pathogens that would compete and succeed the battle of intake is also covered with this review. These manipulated siderophore would enter pathogenic cell like any other siderophore but will not disperse iron due to which iron inadequacy and hence pathogens control be accomplished. The aim of this review is to offer strategies to overcome the microbial infections/pathogens using siderophore.

Empirical power laws for the radii of gyration of protein oligomers

The radius of gyration is a fundamental structural parameter that is particularly useful for describing polymers. It has been known since Flory's seminal work in the mid-20th century that polymers show a power-law dependence, where the radius of gyration is proportional to the number of residues raised to a power. The power-law exponent has been measured experimentally for denatured proteins and derived empirically for folded monomeric proteins using crystal structures. Here, the biological assemblies in the Protein Data Bank are surveyed to derive the power-law parameters for protein oligomers having degrees of oligomerization of 2-6 and 8. The power-law exponents for oligomers span a narrow range of 0.38-0.41, which is close to the value of 0.40 obtained for monomers. This result shows that protein oligomers exhibit essentially the same power-law behavior as monomers. A simple power-law formula is provided for estimating the oligomeric state from an experimental measurement of the radius of gyration. Several proteins in the Protein Data Bank are found to deviate substantially from power-law behavior by having an atypically large radius of gyration. Some of the outliers have highly elongated structures, such as coiled coils. For coiled coils, the radius of gyration does not follow a power law and instead scales linearly with the number of residues in the oligomer. Other outliers are proteins whose oligomeric state or quaternary structure is incorrectly annotated in the Protein Data Bank. The power laws could be used to identify such errors and help prevent them in future depositions.

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.

Ormosil gels doped with engineered catechol 1,2 dioxygenases for chlorocatechol bioremediation

Enzymes entrapped in wet, nanoporous silica gel have great potential as bioreactors for bioremediation because of their improved thermal, chemical, and mechanical stability with respect to enzymes in solution. The B isozyme of catechol 1,2 dioxygenase from Acinetobacter radioresistens and its mutants of Leu69 and Ala72, designed for an increased reactivity toward the environmental pollutant chlorocatechols, were encapsulated using alkoxysilanes and alkyl alkoxysilanes as precursors in varying proportions. Encapsulation of the mutants in a hydrophobic tetramethoxysilane/dimethoxydimethylsilane-based matrix yielded a remarkable 10- to 12-fold enhancement in reactivity toward chlorocatechols. These gels also showed a fivefold increase in relative reactivity toward chlorocatechols with respect to the natural substrate catechol, thus compensating for their relatively low activity for these substrates in solution. The encapsulated enzyme, unlike the enzyme in solution, proved resilient in assays carried out in urban wastewater and bacteria-contaminated solutions mimicking environmentally relevant conditions. Overall, the combination of a structure-based rational design of enzyme mutants, and the selection of a suitable encapsulation material, proved to be a powerful approach for the production and optimization of a potential bioremediation device, with increased activity and resistance toward bacterial degradation.

Fusion of dioxygenase and lignin-binding domains in a novel secreted enzyme from cellulolytic Streptomyces sp. SirexAA-E

Streptomyces sp. SirexAA-E is a highly cellulolytic bacterium isolated from an insect/microbe symbiotic community. When grown on lignin-containing biomass, it secretes SACTE_2871, an aromatic ring dioxygenase domain fused to a family 5/12 carbohydrate-binding module (CBM 5/12). Here we present structural and catalytic studies of this novel fusion enzyme, thus providing insight into its function. The dioxygenase domain has the core β-sandwich fold typical of this enzyme family but lacks a dimerization domain observed in other intradiol dioxygenases. Consequently, the x-ray structure shows that the enzyme is monomeric and the Fe(III)-containing active site is exposed to solvent in a shallow depression on a planar surface. Purified SACTE_2871 catalyzes the O2-dependent intradiol cleavage of catechyl compounds from lignin biosynthetic pathways, but not their methylated derivatives. Binding studies show that SACTE_2871 binds synthetic lignin polymers and chitin through the interactions of the CBM 5/12 domain, representing a new binding specificity for this fold-family. Based on its unique structural features and functional properties, we propose that SACTE_2871 contributes to the invasive nature of the insect/microbial community by destroying precursors needed by the plant for de novo lignin biosynthesis as part of its natural wounding response.

Amphipatic molecules affect the kinetic profile of Pseudomonas putida chlorocatechol 1,2-dioxygenase

Dioxygenases are nonheme iron enzymes that biodegrade recalcitrant compounds, such as catechol and derivatives, released into the environment by modern industry. Intradiol dioxygenases have attracted much attention due to the interest in their use for bioremediation, which has demanded efforts towards understanding their action mechanism and also how to control it. The role of unexpected amphipatic molecules, observed in crystal structures of intradiol dioxygenases, during catalysis has been poorly explored. We report results obtained with the intradiol enzyme chlorocatechol 1,2-dioxygenase (1,2-CCD) from Pseudomonas putida subjected to delipidation. The delipidated enzyme is more stable and shows more cooperative thermal denaturation. The kinetics changes from Michaelis-Menten to a cooperative scheme, indicating that conformational changes propagate between monomers in the absence of amphipatic molecules. Furthermore, these molecules inhibit catalysis, yielding lower v(max) values. To the best of our knowledge, this is the first report concerning the effects of amphipatic molecules on 1,2-CCD function.

X-ray crystallographic and molecular docking studies on a unique chloromuconolactone dehalogenase from Rhodococcus opacus 1CP

5-Chloromuconolactone dehalogenase (5-CMLD) is a unique enzyme that catalyzes the conversion of 5-chloromuconolactone into cis-dienelactone in the new modified ortho-pathway of the 3-chlorocatechol degradation by Rhodococcus opacus 1CP. In all other known chlorocatechol pathways the dehalogenation is a spontaneous secondary reaction of the unstable chloromuconate intermediate following the lactonization process catalyzed by the muconate cycloisomerases. The crystallographic structure of the decameric 5-CMLD was solved by Molecular Replacement, using the coordinates of the low resolution structure of the highly homologous muconolactone isomerase, an enzyme of the conventional ortho-pathway. Muconolactone isomerase catalyzes the endocyclic rearrangement of the double bond within the lactone ring of muconolactone to yield 3-oxoadipate enol lactone. Although both 5-CMLD and muconolactone isomerase share the ability to dechlorinate 5-chloromuconolactone, 5-CMLD shows a significant degree of specialization, having lost the capacity to convert its original substrate muconolactone. The active site of 5-CMLD was previously hypothesized to reside in a deep pocket at the interface of two different subunits, on the basis of a muconolactone isomerase structure analysis. In this study we also performed molecular docking calculations that confirmed these previous findings, and allowed us furthermore to determine the residues involved in the catalytic process.

An EPR, thermostability and pH-dependence study of wild-type and mutant forms of catechol 1,2-dioxygenase from Acinetobacter radioresistens S13

Intradiol dioxygenase are iron-containing enzymes involved in the bacterial degradation of natural and xenobiotic aromatic compounds. The wild-type and mutants forms of catechol 1,2-dioxygenase Iso B from Acinetobacter radioresistens LMG S13 have been investigated in order to get an insight on the structure-function relationships within this system. 4K CW-EPR spectroscopy highlighted different oxygen binding properties of some mutants with respect to the wild-type enzyme, suggesting that a fine tuning of the substrate-binding determinants in the active site pocket may indirectly result in variations of the iron reactivity. A thermostability investigation by optical spectroscopy, that reports on the state of the metal center, showed that the structural stability is more influenced by the type rather than by the position of the mutation. Finally, the influence of pH and temperature on the catalytic activity was monitored and discussed in terms of perturbations induced on the tertiary contact network of the enzyme.

Crystallization and preliminary X-ray diffraction analysis of recombinant chlorocatechol 1,2-dioxygenase from Pseudomonas putida

Chlorocatechol 1,2-dioxygenase from the Gram-negative bacterium Pseudomonas putida (Pp 1,2-CCD) is considered to be an important biotechnological tool owing to its ability to process a broad spectrum of organic pollutants. In the current work, the crystallization, crystallographic characterization and phasing of the recombinant Pp 1,2-CCD enzyme are described. Reddish-brown crystals were obtained in the presence of polyethylene glycol and magnesium acetate by utilizing the vapour-diffusion technique in sitting drops. Crystal dehydration was the key step in obtaining data sets, which were collected on the D03B-MX2 beamline at the CNPEM/MCT - LNLS using a MAR CCD detector. Pp 1,2-CCD crystals belonged to space group P6(1)22 and the crystallographic structure of Pp 1,2-CCD has been solved by the MR-SAD technique using Fe atoms as scattering centres and the coordinates of 3-chlorocatechol 1,2-dioxygenase from Rhodococcus opacus (PDB entry 2boy) as the search model. The initial model, which contains three molecules in the asymmetric unit, has been refined to 3.4 Å resolution.

X-ray crystallography, mass spectrometry and single crystal microspectrophotometry: a multidisciplinary characterization of catechol 1,2 dioxygenase

Intradiol-cleaving catechol 1,2 dioxygenases are Fe(III) dependent enzymes that act on catechol and substituted catechols, including chlorocatechols pollutants, by inserting molecular oxygen in the aromatic ring. Members of this class are the object of intense biochemical investigations aimed at the understanding of their catalytic mechanism, particularly for designing mutants with selected catalytic properties. We report here an in depth investigation of catechol 1,2 dioxygenase IsoB from Acinetobacter radioresistens LMG S13 and its A72G and L69A mutants. By applying a multidisciplinary approach that includes high resolution X-rays crystallography, mass spectrometry and single crystal microspectrophotometry, we characterised the phospholipid bound to the enzyme and provided a structural framework to understand the inversion of substrate specificity showed by the mutants. Our results might be of help for the rational design of enzyme mutants showing a biotechnologically relevant substrate specificity, particularly to be used in bioremediation. This article is part of a Special Issue entitled: Protein Structure and Function in the Crystalline State.

Integron gene cassettes and degradation of compounds associated with industrial waste: the case of the Sydney tar ponds

Integrons are genetic platforms that accelerate lateral gene transfer (LGT) among bacteria. They were first detected on plasmids bearing single and multiple drug resistance determinants in human pathogens, and it is abundantly clear that integrons have played a major role in the evolution of this public health menace. Similar genetic elements can be found in nonpathogenic environmental bacteria and in metagenomic environmental DNA samples, and it is reasonable to suppose that integrons have facilitated microbial adaptation through LGT in niches outside infectious disease wards. Here we show that a heavily impacted estuary, exposed for almost a century to products of coal and steel industries, has developed a rich and unique cassette metagenome, containing genes likely to aid in the catabolism of compounds associated with industrial waste found there. In addition, we report that the most abundant cassette recovered in this study is one that encodes a putative LysR protein. This autoregulatory transcriptional regulator is known to activate transcription of linked target genes or unlinked regulons encoding diverse functions including chlorocatechol and dichlorophenol catabolism. Finally, only class 1 integrase genes were amplified in this study despite using different primer sets, and it may be that the cassettes present in the Tar Ponds will prove to be associated with class 1 integrase genes. Nevertheless, our cassette library provides a snapshot of a complex evolutionary process involving integron-meditated LGT likely to be important in natural bioremediation.

Specificity of catechol ortho-cleavage during para-toluate degradation by Rhodococcus opacus 1cp

Degradation of para-toluate by Rhodococcus opacus 1cp was investigated. Activities of the key enzymes of this process, catechol 1,2-dioxygenase and muconate cycloisomerase, are detected in this microorganism. Growth on p-toluate was accompanied by induction of two catechol 1,2-dioxygenases. The substrate specificity and physicochemical properties of one enzyme are identical to those of chlorocatechol 1,2-dioxygenase; induction of the latter enzyme was observed during R. opacus 1cp growth on 4-chlorophenol. The other enzyme isolated from the biomass grown on p-toluate exhibited lower rate of chlorinated substrate cleavage compared to the catechol substrate. However, this enzyme is not identical to the catechol 1,2-dioxygenase cloned in this strain within the benzoate catabolism operon. This supports the hypothesis on the existence of multiple forms of dioxygenases as adaptive reactions of microorganisms in response to environmental stress.