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PubMed2001

Isolation from agricultural soil and characterization of a Sphingomonas sp. able to mineralize the phenylurea herbicide isoproturon.

A soil bacterium (designated strain SRS2) able to metabolize the phenylurea herbicide isoproturon, 3-(4-isopropylphenyl)-1,1-dimethylurea (IPU), was isolated from a previously IPU-treated agricultural soil. Based on a partial analysis of the 16S rRNA gene and the cellular fatty acids, the strain was identified as a Sphingomonas sp. within the alpha-subdivision of the proteobacteria. Strain SRS2 was able to mineralize IPU when provided as a source of carbon, nitrogen, and energy. Supplementing the medium with a mixture of amino acids considerably enhanced IPU mineralization. Mineralization of IPU was accompanied by transient accumulation of the metabolites 3-(4-isopropylphenyl)-1-methylurea, 3-(4-isopropylphenyl)-urea, and 4-isopropyl-aniline identified by high-performance liquid chromatography analysis, thus indicating a metabolic pathway initiated by two successive N-demethylations, followed by cleavage of the urea side chain and finally by mineralization of the phenyl structure. Strain SRS2 also transformed the dimethylurea-substituted herbicides diuron and chlorotoluron, giving rise to as-yet-unidentified products. In addition, no degradation of the methoxy-methylurea-substituted herbicide linuron was observed. This report is the first characterization of a pure bacterial culture able to mineralize IPU.

Agriculture↗
PubMed2001

Specific growth rate plays a critical role in hydrogen peroxide resistance of the marine oligotrophic ultramicrobacterium sphingomonas alaskensis strain RB2256.

The marine oligotrophic ultramicrobacterium Sphingomonas alaskensis RB2256 has a physiology that is distinctly different from that of typical copiotrophic marine bacteria, such as Vibrio angustum S14. This includes a high level of inherent stress resistance and the absence of starvation-induced stress resistance to hydrogen peroxide. In addition to periods of starvation in the ocean, slow, nutrient-limited growth is likely to be encountered by oligotrophic bacteria for substantial periods of time. In this study we examined the effects of growth rate on the resistance of S. alaskensis RB2256 to hydrogen peroxide under carbon or nitrogen limitation conditions in nutrient-limited chemostats. Glucose-limited cultures of S. alaskensis RB2256 at a specific growth rate of 0.02 to 0.13 h(-1) exhibited 10,000-fold-greater viability following 60 min of exposure to 25 mM hydrogen peroxide than cells growing at a rate of 0.14 h(-1) or higher. Growth rate control of stress resistance was found to be specific to carbon and energy limitation in this organism. In contrast, V. angustum S14 did not exhibit growth rate-dependent stress resistance. The dramatic switch in stress resistance that was observed under carbon and energy limitation conditions has not been described previously in bacteria and thus may be a characteristic of the oligotrophic ultramicrobacterium. Catalase activity varied marginally and did not correlate with the growth rate, indicating that hydrogen peroxide breakdown was not the primary mechanism of resistance. More than 1,000 spots were resolved on silver-stained protein gels for cultures growing at rates of 0.026, 0.076, and 0.18 h(-1). Twelve protein spots had intensities that varied by more than twofold between growth rates and hence are likely to be important for growth rate-dependent stress resistance. These studies demonstrated the crucial role that nutrient limitation plays in the physiology of S. alaskensis RB2256, especially under oxidative stress conditions.

Catalase↗
PubMed2002

Cloning and characterization of lin genes responsible for the degradation of Hexachlorocyclohexane isomers by Sphingomonas paucimobilis strain B90.

Hexachlorocyclohexane (HCH) has been used extensively against agricultural pests and in public health programs for the control of mosquitoes. Commercial formulations of HCH consist of a mixture of four isomers, alpha, beta, gamma, and delta. While all these isomers pose serious environmental problems, beta-HCH is more problematic due to its longer persistence in the environment. We have studied the degradation of HCH isomers by Sphingomonas paucimobilis strain B90 and characterized the lin genes encoding enzymes from strain B90 responsible for the degradation of HCH isomers. Two nonidentical copies of the linA gene encoding HCH dehydrochlorinase, which were designated linA1 and linA2, were found in S. paucimobilis B90. The linA1 and linA2 genes could be expressed in Escherichia coli, leading to dehydrochlorination of alpha-, gamma-, and delta-HCH but not of beta-HCH, suggesting that S. paucimobilis B90 contains another pathway for the initial steps of beta-HCH degradation. The cloning and characterization of the halidohydrolase (linB), dehydrogenase (linC and linX), and reductive dechlorinase (linD) genes from S. paucimobilis B90 revealed that they share approximately 96 to 99% identical nucleotides with the corresponding genes of S. paucimobilis UT26. No evidence was found for the presence of a linE-like gene, coding for a ring cleavage dioxygenase, in strain B90. The gene structures around the linA1 and linA2 genes of strain B90, compared to those in strain UT26, are suggestive of a recombination between linA1 and linA2, which formed linA of strain UT26.

Bacterial Proteins↗
PubMed2002

Cloning and characterization of linR, involved in regulation of the downstream pathway for gamma-hexachlorocyclohexane degradation in Sphingomonas paucimobilis UT26.

In Sphingomonas paucimobilis UT26, LinD and LinE activities, which are responsible for the degradation of gamma-hexachlorocyclohexane, are inducibly expressed in the presence of their substrates, 2,5-dichlorohydroquinone (2,5-DCHQ) and chlorohydroquinone (CHQ). The nucleotide sequence of the 1-kb upstream region of the linE gene was determined, and an open reading frame (ORF) was found in divergent orientation from linE. Because the putative protein product of the ORF showed similarity to the LysR-type transcriptional regulator (LTTR) family, we named it linR. The fragment containing the putative LTTR recognition sequence (a palindromic TN(11)A sequence), which exists immediately upstream of linE, was ligated with the reporter gene lacZ and was inserted into the plasmid expressing LinR under the control of the lac promoter. When the resultant plasmid was introduced into Escherichia coli, the LacZ activity rose in the presence of 2,5-DCHQ and CHQ. RNA slot blot analysis for the total RNAs of UT26 and UT102, which has an insertional mutation in linR, revealed that the expression of the linD and linE genes was induced in the presence of 2,5-DCHQ, CHQ, and hydroquinone in UT26 but not in UT102. These results indicated that the linR gene is directly involved in the inducible expression of the linD and linE genes.

Amino Acid Sequence↗
PubMed2002

Biotransformation of 2,7-dichloro- and 1,2,3,4-tetrachlorodibenzo-p-dioxin by Sphingomonas wittichii RW1.

Aerobic biotransformation of the diaryl ethers 2,7-dichlorodibenzo-p-dioxin and 1,2,3,4-tetrachlorodibenzo-p-dioxin by the dibenzo-p-dioxin-utilizing strain Sphingomonas wittichii RW1, producing corresponding metabolites, was demonstrated for the first time. Our strain transformed 2,7-dichlorodibenzo-p-dioxin, yielding 4-chlorocatechol, and 1,2,3,4-tetrachlorodibenzo-p-dioxin, producing 3,4,5,6-tetrachlorocatechol and 2-methoxy-3,4,5,6-tetrachlorophenol; all of these compounds were unequivocally identified by mass spectrometry both before and after N,O-bis(trimethylsilyl)-trifluoroacetamide derivatization by comparison with authentic standards. Additional experiments showed that strain RW1 formed a second metabolite, 2-methoxy-3,4,5,6-tetrachlorophenol, from the original degradation product, 3,4,5,6-tetrachlorocatechol, by methylation of one of the two hydroxy substituents.

Biotransformation↗
PubMed2002

Identification of quinoide redox mediators that are formed during the degradation of naphthalene-2-sulfonate by Sphingomonas xenophaga BN6.

During aerobic degradation of naphthalene-2-sulfonate (2NS), Sphingomonas xenophaga strain BN6 produces redox mediators which significantly increase the ability of the strain to reduce azo dyes under anaerobic conditions. It was previously suggested that 1,2-dihydroxynaphthalene (1,2-DHN), which is an intermediate in the degradative pathway of 2NS, is the precursor of these redox mediators. In order to analyze the importance of the formation of 1,2-DHN, the dihydroxynaphthalene dioxygenase gene (nsaC) was disrupted by gene replacement. The resulting strain, strain AKE1, did not degrade 2NS to salicylate. After aerobic preincubation with 2NS, strain AKE1 exhibited much higher reduction capacities for azo dyes under anaerobic conditions than the wild-type strain exhibited. Several compounds were present in the culture supernatants which enhanced the ability of S. xenophaga BN6 to reduce azo dyes under anaerobic conditions. Two major redox mediators were purified from the culture supernatants, and they were identified by high-performance liquid chromatography-mass spectrometry and comparison with chemically synthesized standards as 4-amino-1,2-naphthoquinone and 4-ethanolamino-1,2-naphthoquinone.

Anaerobiosis↗
PubMed2002

Characterization of the 5-carboxyvanillate decarboxylase gene and its role in lignin-related biphenyl catabolism in Sphingomonas paucimobilis SYK-6.

Sphingomonas paucimobilis SYK-6 degrades a lignin-related biphenyl compound, 5,5'-dehydrodivanillate (DDVA), to 5-carboxyvanillate (5CVA) by the enzyme reactions catalyzed by the DDVA O-demethylase (LigX), the ring cleavage oxygenase (LigZ), and the meta-cleavage compound hydrolase (LigY). In this study we examined the degradation step of 5CVA. 5CVA was transformed to vanillate, O-demethylated, and further degraded via the protocatechuate 4,5-cleavage pathway by this strain. A cosmid clone which conferred the 5CVA degradation activity to a host strain was isolated. In the 7.0-kb EcoRI fragment of the cosmid we found a 1,002-bp open reading frame responsible for the conversion of 5CVA to vanillate, and we designated it ligW. The gene product of ligW (LigW) catalyzed the decarboxylation of 5CVA to produce vanillate along with the specific incorporation of deuterium from deuterium oxide, indicating that LigW is a nonoxidative decarboxylase of 5CVA. LigW did not require any metal ions or cofactors for its activity. The decarboxylase activity was specific to 5CVA. Inhibition experiments with 5CVA analogs suggested that two carboxyl groups oriented meta to each other in 5CVA are important to the substrate recognition by LigW. Gene walking analysis indicated that the ligW gene was located on the 18-kb DNA region with other DDVA catabolic genes, including ligZ, ligY, and ligX.

Bacterial Proteins↗
PubMed2002

Cloning and characterization of the ferulic acid catabolic genes of Sphingomonas paucimobilis SYK-6.

Sphingomonas paucimobilis SYK-6 degrades ferulic acid to vanillin, and it is further metabolized through the protocatechuate 4,5-cleavage pathway. We obtained a Tn5 mutant of SYK-6, FA2, which was able to grow on vanillic acid but not on ferulic acid. A cosmid which complemented the growth deficiency of FA2 on ferulic acid was isolated. The 5.2-kb BamHI-EcoRI fragment in this cosmid conferred the transformation activity of ferulic acid to vanillin on Escherichia coli host cells. A sequencing analysis revealed the genes ferB and ferA in this fragment; these genes consist of 852- and 2,127-bp open reading frames, respectively. The deduced amino acid sequence of ferB showed 40 to 48% identity with that of the feruloyl-coenzyme A (CoA) hydratase/lyase genes of Pseudomonas and Amycolatopsis ferulic acid degraders. On the other hand, the deduced amino acid sequence of ferA showed no significant similarity to the feruloyl-CoA synthetase genes of other ferulic acid degraders. However, the deduced amino acid sequence of ferA did show 31% identity with pimeloyl-CoA synthetase of Pseudomonas mendocina 35, which has been classified as a new superfamily of acyl-CoA synthetase (ADP forming) with succinyl-CoA synthetase (L. B. Sánchez, M. Y. Galperin, and M. Müller, J. Biol. Chem. 275:5794-5803, 2000). On the basis of the enzyme activity of E. coli carrying each of these genes, ferA and ferB were shown to encode a feruloyl-CoA synthetase and feruloyl-CoA hydratase/lyase, respectively. p-coumaric acid, caffeic acid, and sinapinic acid were converted to their corresponding benzaldehyde derivatives by the cell extract containing FerA and FerB, thereby indicating their broad substrate specificities. We found a ferB homolog, ferB2, upstream of a 5-carboxyvanillic acid decarboxylase gene (ligW) involved in the degradation of 5,5'-dehydrodivanillic acid. The deduced amino acid sequence of ferB2 showed 49% identity with ferB, and its gene product showed feruloyl-CoA hydratase/lyase activity with a substrate specificity similar to that of FerB. Insertional inactivation of each fer gene in S. paucimobilis SYK-6 suggested that the ferA gene is essential and that ferB and ferB2 genes are involved in ferulic acid degradation.

Amino Acid Sequence↗
PubMed2003

Wide geographic distribution of bacteriophages that lyse the same indigenous freshwater isolate (Sphingomonas sp. strain B18).

An indigenous freshwater bacterium (Sphingomonas sp. strain B18) from Lake Plubetasee (Schleswig-Holstein, Germany) was used to isolate 44 phages from 13 very different freshwater and brackish habitats in distant geographic areas. This bacterial strain was very sensitive to a broad spectrum of phages from different aquatic environments. Phages isolated from geographically distant aquatic habitats, but also those from the same sample, were diverse with respect to morphology and restriction pattern. Some phages were widely distributed, while different types coexisted in the same sample. It was concluded that phages could be a major factor in shaping the structure of bacterial communities and maintaining a high bacterial diversity.

Bacteriophages↗
PubMed2004

Genetic analysis of phenoxyalkanoic acid degradation in Sphingomonas herbicidovorans MH.

Phenoxyalkanoic acid degradation is well studied in Beta- and Gammaproteobacteria, but the genetic background has not been elucidated so far in Alphaproteobacteria. We report the isolation of several genes involved in dichlor- and mecoprop degradation from the alphaproteobacterium Sphingomonas herbicidovorans MH and propose that the degradation proceeds analogously to that previously reported for 2,4-dichlorophenoxyacetic acid (2,4-D). Two genes for alpha-ketoglutarate-dependent dioxygenases, sdpA(MH) and rdpA(MH), were found, both of which were adjacent to sequences with potential insertion elements. Furthermore, a gene for a dichlorophenol hydroxylase (tfdB), a putative regulatory gene (cadR), two genes for dichlorocatechol 1,2-dioxygenases (dccA(I/II)), two for dienelactone hydrolases (dccD(I/II)), part of a gene for maleylacetate reductase (dccE), and one gene for a potential phenoxyalkanoic acid permease were isolated. In contrast to other 2,4-D degraders, the sdp, rdp, and dcc genes were scattered over the genome and their expression was not tightly regulated. No coherent pattern was derived on the possible origin of the sdp, rdp, and dcc pathway genes. rdpA(MH) was 99% identical to rdpA(MC1), an (R)-dichlorprop/alpha-ketoglutarate dioxygenase from Delftia acidovorans MC1, which is evidence for a recent gene exchange between Alpha- and Betaproteobacteria. Conversely, DccA(I) and DccA(II) did not group within the known chlorocatechol 1,2-dioxygenases, but formed a separate branch in clustering analysis. This suggests a different reservoir and reduced transfer for the genes of the modified ortho-cleavage pathway in Alphaproteobacteria compared with the ones in Beta- and Gammaproteobacteria.

2,4-Dichlorophenoxyacetic Acid↗
PubMed2004

Dynamics of multiple lin gene expression in Sphingomonas paucimobilis B90A in response to different hexachlorocyclohexane isomers.

Sphingomonas paucimobilis B90A is able to degrade the alpha-, beta-, gamma-, and delta-isomers of hexachlorocyclohexane (HCH). It contains the genes linA, linB, linC, linD, linE, and linR, which have been implicated in HCH degradation. In this study, dynamic expression of the lin genes was measured in chemostat-grown S. paucimobilis B90A by RNA dot blot hybridization and real-time reverse transcriptase PCR upon exposure to a pulse of different HCH isomers. Irrespective of the addition of HCH, linA, linB, and linC were all expressed constitutively. In contrast, linD and linE were induced with alpha-HCH (2 mg/liter) and gamma-HCH (7 mg/liter). A sharp increase in mRNA levels for linD and linE was observed from 10 to 45 min after the addition of alpha- or gamma-HCH. Induction of linD and linE was not detectable upon the addition of 0.7 mg of gamma-HCH per liter, although the compound was degraded by the cells. The addition of beta-HCH (5 mg/liter) or delta-HCH (20 mg/liter) did not lead to linE and linD induction, despite the fact that 50% of the compounds were degraded. This suggests that degradation of beta- and delta-HCH proceeds by a different pathway than that of alpha- and gamma-HCH.

Bacterial Proteins↗
PubMed2004

Identification and functional analysis of two aromatic-ring-hydroxylating dioxygenases from a sphingomonas strain that degrades various polycyclic aromatic hydrocarbons.

In this study, the enzymes involved in polycyclic aromatic hydrocarbon (PAH) degradation in the chrysene-degrading organism Sphingomonas sp. strain CHY-1 were investigated. [14C]chrysene mineralization experiments showed that PAH-grown bacteria produced high levels of chrysene-catabolic activity. One PAH-induced protein displayed similarity with a ring-hydroxylating dioxygenase beta subunit, and a second PAH-induced protein displayed similarity with an extradiol dioxygenase. The genes encoding these proteins were cloned, and sequence analysis revealed two distinct loci containing clustered catabolic genes with strong similarities to corresponding genes found in Novosphingobium aromaticivorans F199. In the first locus, two genes potentially encoding a terminal dioxygenase component, designated PhnI, were followed by a gene coding for an aryl alcohol dehydrogenase (phnB). The second locus contained five genes encoding an extradiol dioxygenase (phnC), a ferredoxin (phnA3), another oxygenase component (PhnII), and an isomerase (phnD). PhnI was found to be capable of converting several PAHs, including chrysene, to the corresponding dihydrodiols. The activity of PhnI was greatly enhanced upon coexpression of genes encoding a ferredoxin (phnA3) and a reductase (phnA4). Disruption of the phnA1a gene encoding the PhnI alpha subunit resulted in a mutant strain that had lost the ability to grow on PAHs. The recombinant PhnII enzyme overproduced in Escherichia coli functioned as a salicylate 1-hydroxylase. PhnII also used methylsalicylates and anthranilate as substrates. Our results indicated that a single enzyme (PhnI) was responsible for the initial attack of a range of PAHs, including chrysene, in strain CHY-1. Furthermore, the conversion of salicylate to catechol was catalyzed by a three-component oxygenase unrelated to known salicylate hydroxylases.

Amino Acid Sequence↗
PubMed2004

Degradation of a nonylphenol single isomer by Sphingomonas sp. strain TTNP3 leads to a hydroxylation-induced migration product.

Sphingomonas sp. strain TTNP3 degrades 4(3',5'-dimethyl-3'-heptyl)-phenol and unidentified metabolites that were described previously. The chromatographic analyses of the synthesized reference compound and the metabolites led to their identification as 2(3',5'-dimethyl-3'-heptyl)-1,4-benzenediol. This finding indicates that the nonylphenol metabolism of this bacterium involves unconventional degradation pathways where an NIH shift mechanism occurs.

Benzene Derivatives↗
PubMed2004

Requirement of a relatively high threshold level of Mg(2+) for cell growth of a rhizoplane bacterium, Sphingomonas yanoikuyae EC-S001.

Mg(2+) is one of the essential elements for bacterial cell growth. The presence of the magnesium cation (Mg(2+)) in various concentrations often affects cell growth restoration in plant-associating bacteria. This study attempted to determine whether Mg(2+) levels in Sphingomonas yanoikuyae EC-S001 affected cell growth restoration in the host plant and what the threshold level is. S. yanoikuyae EC-S001, isolated from the rhizoplane of spinach seedlings grown from surface-sterilized seeds under aseptic conditions, displayed uniform dispersion and attachment throughout the rhizoplane and phylloplane of the host seedlings. S. yanoikuyae EC-S001 did not grow in potato-dextrose broth medium but grew well in an aqueous extract of spinach leaves. Chemical investigation of the growth factor in the spinach leaf extract led to identification of the active principle as the magnesium cation. A concentration of ca. 0.10 mM Mg(2+) or more allowed S. yanoikuyae EC-S001 to grow in potato-dextrose broth medium. Some saprophytic and/or diazotrophic bacteria used in our experiment were found to have diverse threshold levels for their Mg(2+) requirements. For example, Burkholderia cepacia EC-K014, originally isolated from the rhizoplane of a Melastoma sp., could grow even in Mg(2+)-free Hoagland's no. 2 medium with saccharose and glutamine (HSG medium) and requires a trace level of Mg(2+) for its growth. In contrast, S. yanoikuyae EC-S001, together with Bacillus subtilis IFO12113, showed the most drastic restoring responses to subsequent addition of 0.98 mM Mg(2+) to Mg(2+)-free HSG medium. Our studies concluded that Mg(2+) is more than just the essential trace element needed for cell growth restoration in S. yanoikuyae EC-S001 and that certain nonculturable bacteria may require a higher concentration of Mg(2+) or another specific essential element for their growth.

Bacteriological Techniques↗
PubMed2005

Purification of cytochrome P450 and ferredoxin, involved in bisphenol A degradation, from Sphingomonas sp. strain AO1.

In a previous study (M. Sasaki, J. Maki, K. Oshiman, Y. Matsumura, and T. Tsuchido, Biodegradation 16:449-459, 2005), the cytochrome P450 monooxygenase system was shown to be involved in bisphenol A (BPA) degradation by Sphingomonas sp. strain AO1. In the present investigation, we purified the components of this monooxygenase, cytochrome P450 (P450bisd), ferredoxin (Fd(bisd)), and ferredoxin reductase (Red(bisd)). We demonstrated that P450bisd and Fd(bisd) are homodimeric proteins with molecular masses of 102.3 and 19.1 kDa, respectively, by gel filtration chromatography analysis. Spectroscopic analysis of Fd(bisd) revealed the presence of a putidaredoxin-type [2Fe-2S] cluster. P450(bisd), in the presence of Fd(bisd), Red(bisd), and NADH, was able to convert BPA. The K(m) and kcat values for BPA degradation were 85 +/- 4.7 microM and 3.9 +/- 0.04 min(-1), respectively. NADPH, spinach ferredoxin, and spinach ferredoxin reductase resulted in weak monooxygenase activity. These results indicated that the electron transport system of P450bisd might exhibit strict specificity. Two BPA degradation products of the P450(bisd) system were detected by high-performance liquid chromatography analysis and were thought to be 1,2-bis(4-hydroxyphenyl)-2-propanol and 2,2-bis(4-hydroxyphenyl)-1-propanol based on mass spectrometry-mass spectrometry analysis. This is the first report demonstrating that the cytochrome P450 monooxygenase system in bacteria is involved in BPA degradation.

Air Pollutants, Occupational↗
PubMed2005

Enantioselective transformation of alpha-hexachlorocyclohexane by the dehydrochlorinases LinA1 and LinA2 from the soil bacterium Sphingomonas paucimobilis B90A.

Sphingomonas paucimobilis B90A contains two variants, LinA1 and LinA2, of a dehydrochlorinase that catalyzes the first and second steps in the metabolism of hexachlorocyclohexanes (R. Kumari, S. Subudhi, M. Suar, G. Dhingra, V. Raina, C. Dogra, S. Lal, J. R. van der Meer, C. Holliger, and R. Lal, Appl. Environ. Microbiol. 68:6021-6028, 2002). On the amino acid level, LinA1 and LinA2 were 88% identical to each other, and LinA2 was 100% identical to LinA of S. paucimobilis UT26. Incubation of chiral alpha-hexachlorocyclohexane (alpha-HCH) with Escherichia coli BL21 expressing functional LinA1 and LinA2 S-glutathione transferase fusion proteins showed that LinA1 preferentially converted the (+) enantiomer, whereas LinA2 preferred the (-) enantiomer. Concurrent formation and subsequent dissipation of beta-pentachlorocyclohexene enantiomers was also observed in these experiments, indicating that there was enantioselective formation and/or dissipation of these enantiomers. LinA1 preferentially formed (3S,4S,5R,6R)-1,3,4,5,6-pentachlorocyclohexene, and LinA2 preferentially formed (3R,4R,5S,6S)-1,3,4,5,6-pentachlorocyclohexene. Because enantioselectivity was not observed in incubations with whole cells of S. paucimobilis B90A, we concluded that LinA1 and LinA2 are equally active in this organism. The enantioselective transformation of chiral alpha-HCH by LinA1 and LinA2 provides the first evidence of the molecular basis for the changed enantiomer composition of alpha-HCH in many natural environments. Enantioselective degradation may be one of the key processes determining enantiomer composition, especially when strains that contain only one of the linA genes, such as S. paucimobilis UT26, prevail.

Base Sequence↗
PubMed2005

Differential degradation of nonylphenol isomers by Sphingomonas xenophaga Bayram.

Sphingomonas xenophaga Bayram, isolated from the activated sludge of a municipal wastewater treatment plant, was able to utilize 4-(1-ethyl-1,4-dimethylpentyl)phenol, one of the main isomers of technical nonylphenol mixtures, as a sole carbon and energy source. The isolate degraded 1 mg of 4-(1-ethyl-1,4-dimethylpentyl)phenol/ml in minimal medium within 1 week. Growth experiments with five nonylphenol isomers showed that the three isomers with quaternary benzylic carbon atoms [(1,1,2,4-tetramethylpentyl)phenol, 4-(1-ethyl-1,4-dimethylpentyl)phenol, and 4-(1,1-dimethylheptyl)phenol] served as growth substrates, whereas the isomers containing one or two hydrogen atoms in the benzylic position [4-(1-methyloctyl)phenol and 4-n-nonylphenol] did not. However, when the isomers were incubated as a mixture, all were degraded to a certain degree. Differential degradation was clearly evident, as isomers with more highly branched alkyl side chains were degraded much faster than the others. Furthermore, the C9 alcohols 2,3,5-trimethylhexan-2-ol, 3,6-dimethylheptan-3-ol, and 2-methyloctan-2-ol, derived from the three nonylphenol isomers with quaternary benzylic carbon atoms, were detected in the culture fluid by gas chromatography-mass spectrometry, but no analogous metabolites could be found originating from 4-(1-methyloctyl)phenol and 4-n-nonylphenol. We propose that 4-(1-methyloctyl)phenol and 4-n-nonylphenol were cometabolically transformed in the growth experiments with the mixture but that, unlike the other isomers, they did not participate in the reactions leading to the detachment of the alkyl moiety. This hypothesis was corroborated by the observed accumulation in the culture fluid of an as yet unidentified metabolite derived from 4-(1-methyloctyl)phenol.

Alcohols↗
PubMed2005

Degradation of beta-Hexachlorocyclohexane by Haloalkane Dehalogenase LinB from Sphingomonas paucimobilis UT26.

Beta-Hexachlorocyclohexane (beta-HCH) is the most recalcitrant among the alpha-, beta-, gamma-, and delta-isomers of HCH and causes serious environmental pollution problems. We demonstrate here that the haloalkane dehalogenase LinB, reported earlier to mediate the second step in the degradation of gamma-HCH in Sphingomonas paucimobilis UT26, metabolizes beta-HCH to produce 2,3,4,5,6-pentachlorocyclohexanol.

Bacterial Proteins↗