Metabolism of tetralin (1,2,3,4-tetrahydronaphthalene) in Corynebacterium sp. strain C125

Development of Highly Potent, G-Protein Pathway Biased, Selective, and Orally Bioavailable GPR84 Agonists

Orphan G-protein-coupled receptor 84 (GPR84) is a receptor that has been linked to cancer, inflammatory, and fibrotic diseases. We have reported DL-175 as a biased agonist at GPR84 which showed differential signaling via Gαi/cAMP and β-arrestin, but which is rapidly metabolized. Herein, we describe an optimization of DL-175 through a systematic structure-activity relationship (SAR) analysis. This reveals that the replacement of the naphthalene group improved metabolic stability and the addition of a 5-hydroxy substituent to the pyridine N-oxide group, yielding compounds 68 (OX04528) and 69 (OX04529), enhanced the potency for cAMP signaling by 3 orders of magnitude to low picomolar values. Neither compound showed detectable effects on β-arrestin recruitment up to 80 μM. Thus, the new GPR84 agonists 68 and 69 displayed excellent potency, high G-protein signaling bias, and an appropriate in vivo pharmacokinetic profile that will allow investigation of GPR84 biased agonist activity in vivo.

Nitrification activity in the presence of 2-chlorophenol using whole nitrifying cells and cell-free extracts: batch and SBR assays

Kinetic assays with a nitrifying consortium with whole nitrifying cells amended with 5 mg 2-CP-C/L and 100, 200, 300, or 500 mg NH4+-N/L were carried out in batch and nitrifying sequencing batch reactor (SBR) cultures. No nitrification activity was observed in batch assays with 100 mg NH4+-N/L and 5 mg 2-CP-C/L. Nevertheless, increasing the ammonium concentration from 200 to 500 mg NH4+-N/L allowed simultaneous ammonium and nitrite oxidation even in the presence of 5 mg 2-CP-C/L plus the halogenated compound consumption. Under these conditions, the ammonium monooxygenase enzyme participated in 2-CP consumption. Complete nitrification and simultaneous elimination of 5 mg 2-CP-C/L were achieved in the SBR amended with 200-500 mg NH4+-N/L. The inhibitory effect of 2-CP on the nitrite oxidation process completely disappeared under these conditions. Assays with nitrifying cell-free extracts, ammonium (100 mg NH4+-N/L), and 2-CP (5 mg 2-CP-C/L) were also conducted. In the absence of 2-CP, the nitrifying cell-free extracts maintained up to 60% of the nitrifying activity compared to whole-cells. Contrary to whole-cell assays, cell-free extracts were capable of simultaneously oxidizing ammonium and consuming 2-CP. However, the inhibitory effect of 2-CP on nitrification was still present as lower specific rates of ammonium consumption and nitrate production were obtained. Thus, these assays indicate that the presence of 2-CP affects both, the ammonium transport mechanism and the activity of nitrifying enzymes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03764-z.

Biodegradation of Tetralin: Genomics, Gene Function and Regulation

Tetralin (1,2,3,4-tetrahydonaphthalene) is a recalcitrant compound that consists of an aromatic and an alicyclic ring. It is found in crude oils, produced industrially from naphthalene or anthracene, and widely used as an organic solvent. Its toxicity is due to the alteration of biological membranes by its hydrophobic character and to the formation of toxic hydroperoxides. Two unrelated bacteria, Sphingopyxis granuli strain TFA and Rhodococcus sp. strain TFB were isolated from the same niche as able to grow on tetralin as the sole source of carbon and energy. In this review, we provide an overview of current knowledge on tetralin catabolism at biochemical, genetic and regulatory levels in both strains. Although they share the same biodegradation strategy and enzymatic activities, no evidences of horizontal gene transfer between both bacteria have been found. Moreover, the regulatory elements that control the expression of the gene clusters are completely different in each strain. A special consideration is given to the complex regulation discovered in TFA since three regulatory systems, one of them involving an unprecedented communication between the catabolic pathway and the regulatory elements, act together at transcriptional and posttranscriptional levels to optimize tetralin biodegradation gene expression to the environmental conditions.

Differential degradation of bicyclics with aromatic and alicyclic rings by Rhodococcus sp. strain DK17

The metabolically versatile Rhodococcus sp. strain DK17 is able to grow on tetralin and indan but cannot use their respective desaturated counterparts, 1,2-dihydronaphthalene and indene, as sole carbon and energy sources. Metabolite analyses by gas chromatography-mass spectrometry and nuclear magnetic resonance spectrometry clearly show that (i) the meta-cleavage dioxygenase mutant strain DK180 accumulates 5,6,7,8-tetrahydro-1,2-naphthalene diol, 1,2-indene diol, and 3,4-dihydro-naphthalene-1,2-diol from tetralin, indene, and 1,2-dihydronaphthalene, respectively, and (ii) when expressed in Escherichia coli, the DK17 o-xylene dioxygenase transforms tetralin, indene, and 1,2-dihydronaphthalene into tetralin cis-dihydrodiol, indan-1,2-diol, and cis-1,2-dihydroxy-1,2,3,4-tetrahydronaphthalene, respectively. Tetralin, which is activated by aromatic hydroxylation, is degraded successfully via the ring cleavage pathway to support growth of DK17. Indene and 1,2-dihydronaphthalene do not serve as growth substrates because DK17 hydroxylates them on the alicyclic ring and further metabolism results in a dead-end metabolite. This study reveals that aromatic hydroxylation is a prerequisite for proper degradation of bicyclics with aromatic and alicyclic rings by DK17 and confirms the unique ability of the DK17 o-xylene dioxygenase to perform distinct regioselective hydroxylations.

Oxidation of naphthenoaromatic and methyl-substituted aromatic compounds by naphthalene 1,2-dioxygenase

Oxidation of acenaphthene, acenaphthylene, and fluorene was examined with recombinant strain Pseudomonas aeruginosa PAO1(pRE695) expressing naphthalene dioxygenase genes cloned from plasmid NAH7. Acenaphthene underwent monooxygenation to 1-acenaphthenol with subsequent conversion to 1-acenaphthenone and cis- and trans-acenaphthene-1,2-diols, while acenaphthylene was dioxygenated to give cis-acenaphthene-1,2-diol. Nonspecific dehydrogenase activities present in the host strain led to the conversion of both of the acenaphthene-1,2-diols to 1,2-acenaphthoquinone. The latter was oxidized spontaneously to naphthalene-1,8-dicarboxylic acid. No aromatic ring dioxygenation products were detected from acenaphthene and acenaphthylene. Mixed monooxygenase and dioxygenase actions of naphthalene dioxygenase on fluorene yielded products of benzylic 9-monooxygenation, aromatic ring dioxygenation, or both. The action of naphthalene dioxygenase on a variety of methyl-substituted aromatic compounds, including 1,2,4-trimethylbenzene and isomers of dimethylnaphthalene, resulted in the formation of benzylic alcohols, i.e., methyl group monooxygenation products, which were subsequently converted to the corresponding carboxylic acids by dehydrogenase(s) in the host strain. Benzylic monooxygenation of methyl groups was strongly predominant over aromatic ring dioxygenation and essentially nonspecific with respect to the substitution pattern of the aromatic substrates. In addition to monooxygenating benzylic methyl and methylene groups, naphthalene dioxygenase behaved as a sulfoxygenase, catalyzing monooxygenation of the sulfur heteroatom of 3-methylbenzothiophene.

Sulfonate desulfurization in Rhodococcus from wheat rhizosphere communities

Organically bound sulfur makes up about 90% of the total sulfur in soils, with sulfonates often the dominant fraction. Actinobacteria affiliated to the genus Rhodococcus were able to desulfonate arylsulfonates in wheat rhizospheres from the Broadbalk long-term field wheat experiment, which includes plots treated with inorganic fertilizer with and without sulfate, with farmyard manure, and unfertilized plots. Direct isolation of desulfonating rhizobacteria yielded Rhodococcus strains which grew well with a range of sulfonates, and contained the asfAB genes, known to be involved in sulfonate desulfurization by bacteria. Expression of asfA in vitro increased >100-fold during growth of the Rhodococcus isolates with toluenesulfonate as sulfur source, compared with growth with sulfate. By contrast, the closely related Rhodococcus erythropolis and Rhodococcus opacus type strains had no desulfonating activity and did not contain asfA homologues. The overall actinobacterial community structure in wheat rhizospheres was influenced by the sulfur fertilization regime, as shown by specific denaturing gradient gel electrophoresis of PCR amplified 16S rRNA gene fragments, and asfAB clone library analysis identified nine different asfAB genotypes closely affiliated to the Rhodococcus isolates. However, asfAB-based multiplex restriction fragment length polymorphism (RFLP)/terminal-RFLP analysis of wheat rhizosphere communities revealed only slight differences between the fertilization regimes, suggesting that the desulfonating Rhodococcus community does not specifically respond to changes in sulfate supply.

Functional identification of novel genes involved in the glutathione-independent gentisate pathway in Corynebacterium glutamicum

Corynebacterium glutamicum used gentisate and 3-hydroxybenzoate as its sole carbon and energy source for growth. By genome-wide data mining, a gene cluster designated ncg12918-ncg12923 was proposed to encode putative proteins involved in gentisate/3-hydroxybenzoate pathway. Genes encoding gentisate 1,2-dioxygenase (ncg12920) and fumarylpyruvate hydrolase (ncg12919) were identified by cloning and expression of each gene in Escherichia coli. The gene of ncg12918 encoding a hypothetical protein (Ncg12918) was proved to be essential for gentisate-3-hydroxybenzoate assimilation. Mutant strain RES167Deltancg12918 lost the ability to grow on gentisate or 3-hydroxybenzoate, but this ability could be restored in C. glutamicum upon the complementation with pXMJ19-ncg12918. Cloning and expression of this ncg12918 gene in E. coli showed that Ncg12918 is a glutathione-independent maleylpyruvate isomerase. Upstream of ncg12920, the genes ncg12921-ncg12923 were located, which were essential for gentisate and/or 3-hydroxybenzoate catabolism. The Ncg12921 was able to up-regulate gentisate 1,2-dioxygenase, maleylpyruvate isomerase, and fumarylpyruvate hydrolase activities. The genes ncg12922 and ncg12923 were deduced to encode a gentisate transporter protein and a 3-hydroxybenzoate hydroxylase, respectively, and were essential for gentisate or 3-hydroxybenzoate assimilation. Based on the results obtained in this study, a GSH-independent gentisate pathway was proposed, and genes involved in this pathway were identified.

Key enzymes of the protocatechuate branch of the beta-ketoadipate pathway for aromatic degradation in Corynebacterium glutamicum

Although the protocatechuate branch of the beta-ketoadipate pathway in Gram+ bacteria has been well studied, this branch is less understood in Gram+ bacteria. In this study, Corynebacterium glutamicum was cultivated with protocatechuate, p-cresol, vanillate and 4-hydroxybenzoate as sole carbon and energy sources for growth. Enzymatic assays indicated that growing cells on these aromatic compounds exhibited protocatechuate 3,4-dioxygenase activities. Data-mining of the genome of this bacterium revealed that the genetic locus ncg12314-ncg12315 encoded a putative protocatechuate 3,4-dioxygenase. The genes, ncg12314 and ncg12315, were amplified by PCR technique and were cloned into plasmid (pET21aP34D). Recombinant Escherichia coli strain harboring this plasmid actively expressed protocatechuate 3,4-dioxygenase activity. Further, when this locus was disrupted in C. glutamicum, the ability to degrade and assimilate protocatechuate, p-cresol, vanillate or 4-hydroxybenzoate was lost and protocatechuate 3,4-dioxygenase activity was disappeared. The ability to grow with these aromatic compounds and protocatechuate 3,4-dioxygenase activity of C. glutamicum mutant could be restored by gene complementation. Thus, it is clear that the key enzyme for ring-cleavage, protocatechuate 3,4-dioxygenase, was encoded by ncg12314 and ncg12315. The additional genes involved in the protocatechuate branch of the beta-ketoadipate pathway were identified by mining the genome data publically available in the GenBank. The functional identification of genes and their unique organization in C. glutamicum provided new insight into the genetic diversity of aromatic compound degradation.

Stable long-term indigo production by overexpression of dioxygenase genes using a chromosomal integrated cascade expression circuit

In our laboratory we have analyzed different factors to maximize the yield in heterologous protein expression for long-term cultivation, by combination of an efficient cascade expression system and stable integration in the bacterial chromosome. In this work, we have explored this system for the production of indigo dye as a model for biotechnological production, by expressing in Escherichia coli the thnA1A2A3A4 genes from Sphingomonas macrogolitabida strain TFA, which encode the components of a tetralin dioxygenase activity. We compared Ptac, and the Pm-based cascade expression circuit in a multicopy plasmid and stably integrated into the bacterial chromosome. Plasmid-based expression systems resulted in instability of indigo production when serially diluted batch experiments were performed without a selective pressure. This problem was solved by integrating the expression module in the chromosome. Despite the gene dosage reduction, the synergic effect of the cascade expression system produced comparable expression to the dioxygenase activity in the plasmid configuration but could be stably maintained for at least 5 days. Here, we show that the cascade amplification circuit integrated in the chromosome could be an excellent system for tight control and stable production of recombinant products.

Regulation of tetralin biodegradation and identification of genes essential for expression of thn operons

The tetralin biodegradation genes of Sphingomonas macrogolitabida strain TFA are clustered in two closely linked and divergent operons. To analyze expression of both operons under different growth conditions, transcriptional and translational gene fusions of the first genes of each operon to lacZ have been constructed in plasmids unable to replicate in Sphingomonas and integrated by recombination into the genome of strain TFA. Expression analysis indicated that the transcription of both genes is induced in similar ways by the presence of tetralin. Gene expression in both operons is also subjected to overimposed catabolic repression. Two additional genes named thnR and thnY have been identified downstream of thnCA3A4 genes. ThnR is similar to LysR-type regulators, and mutational analysis indicated that ThnR is strictly required for expression of the thn operons. Unlike other LysR-type regulators, ThnR does not repress its own synthesis. In fact, ThnR activates its own expression, since thnR is cotranscribed with the thnCA3A4 genes. ThnY is similar to the ferredoxin reductase components of dioxygenase systems and shows the fer2 domain, binding a Cys4[2Fe-2S] iron sulfur center, and the FAD-binding domain, common to those reductases. However, it lacks the NAD-binding domain. Intriguingly, ThnY has a regulatory role, since it is also strictly required for expression of the thn operons. Given the similarity of ThnY to reductases and the possibility of its being present in the two redox states, it is tempting to speculate that ThnY is a regulatory component connecting expression of the thn operons to the physiological status of the cell.

Identification and functional characterization of Sphingomonas macrogolitabida strain TFA genes involved in the first two steps of the tetralin catabolic pathway

Five genes involved in the two initial steps of the tetralin biodegradation pathway of Sphingomonas macrogolitabida strain TFA have been characterized. ThnA1A2 and ThnA3A4, components of the ring-hydroxylating dioxygenase, were encoded in divergently transcribed operons. ThnA1, ThnA2, and ThnA3 were essential for tetralin ring-hydroxylating dioxygenase activity. ThnB was identified as a dehydrogenase required for tetralin biodegradation.

Identification of a hydratase and a class II aldolase involved in biodegradation of the organic solvent tetralin

Two new genes whose products are involved in biodegradation of the organic solvent tetralin were identified. These genes, designated thnE and thnF, are located downstream of the previously identified thnD gene and code for a hydratase and an aldolase, respectively. A sequence comparison of enzymes similar to ThnE showed the significant similarity of hydratases involved in biodegradation pathways to 4-oxalocrotonate decarboxylases and established four separate groups of related enzymes. Consistent with the sequence information, characterization of the reaction catalyzed by ThnE showed that it hydrated a 10-carbon dicarboxylic acid. The only reaction product detected was the enol tautomer, 2,4-dihydroxydec-2-ene-1,10-dioic acid. The aldolase ThnF showed significant similarity to aldolases involved in different catabolic pathways whose substrates are dihydroxylated dicarboxylic acids and which yield pyruvate and a semialdehyde. The reaction products of the aldol cleavage reaction catalyzed by ThnF were identified as pyruvate and the seven-carbon acid pimelic semialdehyde. ThnF and similar aldolases showed conservation of the active site residues identified by the crystal structure of 2-dehydro-3-deoxy-galactarate aldolase, a class II aldolase with a novel reaction mechanism, suggesting that these similar enzymes are class II aldolases. In contrast, ThnF did not show similarity to 4-hydroxy-2-oxovalerate aldolases of other biodegradation pathways, which are significantly larger and apparently are class I aldolases.

Monocyclic aromatic hydrocarbon degradation by Rhodococcus sp. strain DK17

Rhodococcus sp. strain DK17 was isolated from soil and analyzed for the ability to grow on o-xylene as the sole carbon and energy source. Although DK17 cannot grow on m- and p-xylene, it is capable of growth on benzene, phenol, toluene, ethylbenzene, isopropylbenzene, and other alkylbenzene isomers. One UV-generated mutant strain, DK176, simultaneously lost the ability to grow on o-xylene, ethylbenzene, isopropylbenzene, toluene, and benzene, although it could still grow on phenol. The mutant strain was also unable to oxidize indole to indigo following growth in the presence of o-xylene. This observation suggests the loss of an oxygenase that is involved in the initial oxidation of the (alkyl)benzenes tested. Another mutant strain, DK180, isolated for the inability to grow on o-xylene, retained the ability to grow on benzene but was unable to grow on alkylbenzenes due to loss of a meta-cleavage dioxygenase needed for metabolism of methyl-substituted catechols. Further experiments showed that DK180 as well as the wild-type strain DK17 have an ortho-cleavage pathway which is specifically induced by benzene but not by o-xylene. These results indicate that DK17 possesses two different ring-cleavage pathways for the degradation of aromatic compounds, although the initial oxidation reactions may be catalyzed by a common oxygenase. Gas chromatography-mass spectrometry and 300-MHz proton nuclear magnetic resonance spectrometry clearly show that DK180 accumulates 3,4-dimethylcatechol from o-xylene and both 3- and 4-methylcatechol from toluene. This means that there are two initial routes of oxidation of toluene by the strain. Pulsed-field gel electrophoresis analysis demonstrated the presence of two large megaplasmids in the wild-type strain DK17, one of which (pDK2) was lost in the mutant strain DK176. Since several other independently derived mutant strains unable to grow on alkylbenzenes are also missing pDK2, the genes encoding the initial steps in alkylbenzene metabolism (but not phenol metabolism) appear to be present on this approximately 330-kb plasmid.

Identification of a serine hydrolase which cleaves the alicyclic ring of tetralin

A gene designated thnD, which is required for biodegradation of the organic solvent tetralin by Sphingomonas macrogoltabidus strain TFA, has been identified. Sequence comparison analysis indicated that thnD codes for a carbon-carbon bond serine hydrolase showing highest similarity to hydrolases involved in biodegradation of biphenyl. An insertion mutant defective in ThnD accumulates the ring fission product which results from the extradiol cleavage of the aromatic ring of dihydroxytetralin. The gene product has been purified and characterized. ThnD is an octameric thermostable enzyme with an optimum reaction temperature at 65 degrees C. ThnD efficiently hydrolyzes the ring fission intermediate of the tetralin pathway and also 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid, the ring fission product of the biphenyl meta-cleavage pathway. However, it is not active towards the equivalent intermediates of meta-cleavage pathways of monoaromatic compounds which have small substituents in C-6. When ThnD hydrolyzes the intermediate in the tetralin pathway, it cleaves a C-C bond comprised within the alicyclic ring of tetralin instead of cleaving a linear C-C bond, as all other known hydrolases of meta-cleavage pathways do. The significance of this activity of ThnD for the requirement of other activities to mineralize tetralin is discussed.

Identification of an extradiol dioxygenase involved in tetralin biodegradation: gene sequence analysis and purification and characterization of the gene product

A genomic region involved in tetralin biodegradation was recently identified in Sphingomonas strain TFA. We have cloned and sequenced from this region a gene designated thnC, which codes for an extradiol dioxygenase required for tetralin utilization. Comparison to similar sequences allowed us to define a subfamily of 1, 2-dihydroxynaphthalene extradiol dioxygenases, which comprises two clearly different groups, and to show that ThnC clusters within group 2 of this subfamily. 1,2-Dihydroxy-5,6,7, 8-tetrahydronaphthalene was found to be the metabolite accumulated by a thnC insertion mutant. The ring cleavage product of this metabolite exhibited behavior typical of a hydroxymuconic semialdehyde toward pH-dependent changes and derivatization with ammonium to give a quinoline derivative. The gene product has been purified, and its biochemical properties have been studied. The enzyme is a decamer which requires Fe(II) for activity and shows high activity toward its substrate (V(max), 40.5 U mg(-1); K(m), 18. 6 microM). The enzyme shows even higher activity with 1, 2-dihydroxynaphthalene and also significant activity toward 1, 2-dihydroxybiphenyl or methylated catechols. The broad substrate specificity of ThnC is consistent with that exhibited by other extradiol dioxygenases of the same group within the subfamily of 1, 2-dihydroxynaphthalene dioxygenases.

Genetic analysis of biodegradation of tetralin by a Sphingomonas strain

A strain designated TFA which very efficiently utilizes tetralin has been isolated from the Rhine river. The strain has been identified as Sphingomonas macrogoltabidus, based on 16S rDNA sequence similarity. Genetic analysis of tetralin biodegradation has been performed by insertion mutagenesis and by physical analysis and analysis of complementation between the mutants. The genes involved in tetralin utilization are clustered in a region of 9 kb, comprising at least five genes grouped in two divergently transcribed operons.

Bacterial transformations of 1,2,3,4-tetrahydrodibenzothiophene and dibenzothiophene

The transformations of 1,2,3,4-tetrahydrodibenzothiophene (THDBT) were investigated with pure cultures of hydrocarbon-degrading bacteria. Metabolites were extracted from cultures with dichloromethane (DCM) and analyzed by gas chromatography (GC) with flame photometric, mass, and Fourier transform infrared detectors. Three 1-methylnaphthalene (1-MN)-utilizing Pseudomonas strains oxidized the sulfur atom of THDBT to give the sulfoxide and sulfone. They also degraded the benzene ring to yield 3-hydroxy-2-formyl-4,5,6,7-tetrahydrobenzothiophene. A cell suspension of a cyclohexane-degrading bacterium oxidized the alicyclic ring to give a hydroxy-substituted THDBT and a ketone, and it oxidized the aromatic ring to give a phenol, but no ring cleavage products were detected. GC analyses with an atomic emission detector, using the sulfur-selective mode, were used to quantify the transformation products from THDBT and dibenzothiophene (DBT). The cyclohexane degrader oxidized 19% of the THDBT to three metabolites. The cometabolism of THDBT and DBT by the three 1-MN-grown Pseudomonas strains resulted in a much greater depletion of the condensed thiophenes than could be accounted for in the metabolites detected by GC analysis, but there was no evidence of sulfate release from DBT. These 1-MN-grown strains transiently accumulated 3-hydroxy-2-formylbenzothiophene (HFBT) from DBT, but it was subsequently degraded. On the other hand, Pseudomonas strain BT1d, which was maintained on DBT as a sole carbon source, accumulated 52% of the sulfur from DBT as HFBT over 7 days, and, in total, 82% of the sulfur from DBT was accounted for by the GC method used. Lyophilization of cultures grown on 1-MN with DBT and methyl esterification of the residues gave improved recoveries of total sulfur over that obtained by DCM extraction and GC analysis. This suggested that the further degradation of HFBT by these cultures leads to the formation of organosulfur compounds that are too polar to be extracted with DCM. We believe that this is the first attempt to quantify the products of DBT degradation by the so-called Kodama pathway.

Growth of rhodococcus S1 on anthracene

Three slow-growing bacteria were isolated from a mixed culture enriched for growth on anthracene, using creosote-contaminated soil as the inoculum. Organisms were shown to use anthracene by the production of a clear zone around the colony after a mineral salts agar plate was sprayed with anthracene. All three bacteria were nonmotile, nonsporulating, gram-positive rods and stained acid-fast. Physiological and biochemical tests, GC content, and cell wall lipid patterns of whole cell methanolysates indicated that they belonged to the Nocardia-Mycobacterium-Rhodococcus group. On the basis of these characteristics and pyrolysis gas chromatography, they were assigned to the genus Rhodococcus. Growth of the isolates was slow on crystalline anthracene, giving a doubling time of 1.5-3 days, and they grew mainly on the crystal surface. When anthracene was supplied by precipitation from a solvent, doubling time was reduced to 1 day. All three isolates mineralized anthracene but not phenanthrene or naphthalene, nor could they grow on naphthalene, phenanthrene, fluorene, fluoranthene, acenaphthene, pyrene, chrysene, or naphthacene as sole carbon source. One isolate, Rhodococcus S1, was able to use 2-methylanthracene or 2-chloroanthracene as carbon source but not 1- or 9-substituted analogs. These results suggest that the initial enzyme attacking anthracene in these isolates has a narrow substrate specificity.

Evidence for a novel pathway in the degradation of fluorene by Pseudomonas sp. strain F274

A fluorene-utilizing microorganism, identified as a species of Pseudomonas, was isolated from soil severely contaminated from creosote use and was shown to accumulate six major metabolites from fluorene in washed-cell incubations. Five of these products were identified as 9-fluorenol, 9-fluorenone, (+)-1,1a-dihydroxy-1-hydro-9-fluorenone, 8-hydroxy-3,4-benzocoumarin, and phthalic acid. This last compound was also identified in growing cultures supported by fluorene. Fluorene assimilation into cell biomass was estimated to be approximately 50%. The structures of accumulated products indicate that a previously undescribed pathway of fluorene catabolism is employed by Pseudomonas sp. strain F274. This pathway involves oxygenation of fluorene at C-9 to give 9-fluorenol, which is then dehydrogenated to the corresponding ketone, 9-fluorenone. Dioxygenase attack on 9-fluorenone adjacent to the carbonyl group gives an angular diol, 1,1a-dihydroxy-1-hydro-9-fluorenone. Identification of 8-hydroxy-3,4-benzocoumarin and phthalic acid suggests that the five-membered ring of the angular diol is opened first and that the resulting 2'-carboxy derivative of 2,3-dihydroxy-biphenyl is catabolized by reactions analogous to those of biphenyl degradation, leading to the formation of phthalic acid. Cell extracts of fluorene-grown cells possessed high levels of an enzyme characteristic of phthalate catabolism, 4,5-dihydroxyphthalate decarboxylase, together with protocatechuate 4,5-dioxygenase. On the basis of these findings, a pathway of fluorene degradation is proposed to account for its conversion to intermediary metabolites. A range of compounds with structures similar to that of fluorene was acted on by fluorene-grown cells to give products consistent with the initial reactions proposed.

Metabolism of styrene by Rhodococcus rhodochrous NCIMB 13259

Rhodococcus rhodochrous NCIMB 13259 grows on styrene, toluene, ethylbenzene, and benzene as sole carbon sources. Simultaneous induction tests with cells grown on styrene or toluene showed high rates of oxygen consumption with toluene cis-glycol and 3-methylcatechol, suggesting the involvement of a cis-glycol pathway. 3-Vinylcatechol accumulated when intact cells were incubated with styrene in the presence of 3-fluorocatechol to inhibit catechol dioxygenase activity. Experiments with 18O2 showed that 3-vinylcatechol was produced following a dioxygenase ring attack. Extracts contained a NAD-dependent cis-glycol dehydrogenase, which converted styrene cis-glycol to 3-vinylcatechol. Both catechol 1,2- and 2,3-dioxygenase activities were present, and these were separated from each other and from the activities of cis-glycol dehydrogenase and 2-hydroxymuconic acid semialdehyde hydrolase by ion-exchange chromatography of extracts. 2-Vinylmuconate accumulated in the growth medium when cells were grown on styrene, apparently as a dead-end product, and extracts contained no detectable muconate cycloisomerase activity. 3-Vinylcatechol was cleaved by catechol 2,3-dioxygenase to give a yellow compound, tentatively identified as 2-hydroxy-6-oxoocta-2,4,7-trienoic acid, and the action of 2-hydroxymuconic acid semialdehyde hydrolase on this produced acrylic acid. A compound with the spectral characteristics of 2-hydroxypenta-2,4-dienoate was produced by the action of 2-hydroxymuconic acid semialdehyde hydrolase on the 2,3-cleavage product of 3-methylcatechol. Extracts were able to transform 2-hydroxypenta-2,4-dienoate and 4-hydroxy-2-oxopentanoate into acetaldehyde and pyruvate.(ABSTRACT TRUNCATED AT 250 WORDS)

Biotransformations catalyzed by the genus Rhodococcus

Rhodococci display a diverse range of metabolic capabilities and they are a ubiquitous feature of many environments. They are able to degrade short-chain, long-chain, and halogenated hydrocarbons, and numerous aromatic compounds, including halogenated and other substituted aromatics, heteroaromatics, hydroaromatics, and polycyclic aromatic hydrocarbons. They possess a wide variety of pathways for degrading and modifying aromatic compounds, including dioxygenase and monooxygenase ring attack, and cleavage of catechol by both ortho- and meta-routes, and some strains possess a modified 3-oxoadipate pathway. Biotransformations catalyzed by rhodococci include steroid modification, enantioselective synthesis, and the transformation of nitriles to amides and acids. Tolerance of rhodococci to starvation, their frequent lack of catabolite repression, and their environmental persistence make them excellent candidates for bioremediation treatments. Some strains can produce poly(3-hydroxyalkanoate)s, others can accumulate cesium, and still others are the source of useful enzymes such as phenylalanine dehydrogenase and endoglycosidases. Other actual or potential applications of rhodococci include desulfurization of coal, bioleaching, use of their surfactants in enhancement of oil recovery and as industrial dispersants, and the construction of biosensors.