Induction of phenol-metabolizing enzymes in Trichosporon cutaneum

Biodegradation of phenol by cold-tolerant bacteria isolated from alpine soils of Binaloud Mountains in Iran

Degradation of phenol is considered to be a challenge because of harsh environments in cold regions and ground waters. Molecular characterization of phenol degrading bacteria was investigated to gain an insight into the biodegradation in cold areas. The psychrotolerant and psychrophiles bacteria were isolated from alpine soils in the northeast of Iran. These strains belonged to Pseudomonas sp., Stenotrophomonas spp. and Shinella spp. based on analysis of the 16S rRNA gene. These strains were capable of the complete phenol degradation at a concentration of 200 mg L^-1 at 20 °C. Moreover, the strains could degrade phenol at a concentration of 400 and 600 mg L^-1 at a higher time. Effects of environmental factors were studied using one factor at a time (OFAT) approach for Pseudomonas sp.ATR208. When the bacterium was grown in a liquid medium with 600 mg L^-1 of concentration supplemented with optimum carbon and nitrogen sources, more than 99% of phenol removal was obtained at 20 °C and 24 h. Therefore, the present study indicated the potential of the local cold tolerant bacteria in the phenol bioremediation.

Biodegradation of phenol via meta cleavage pathway triggers de novo TAG biosynthesis pathway in oleaginous yeast

Phenol is reported to be one of the most toxic environmental pollutants present in the discharge of various industrial effluents causing a serious threat to the existing biome. Biodegradation of phenol by oleaginous yeast Rhodosporidium kratochvilovae HIMPA1 was found to degrade 1000mg/l phenol. The pathways for phenol degradation by both ortho and meta-cleavage were proposed by the identification of metabolites and enzymatic assays of ring cleavage enzymes in the cell extracts. Results suggest that this oleaginous yeast degrade phenol via meta-cleavage pathway and accumulates a high quantity of lipid content (64.92%; wt/wt) as compared to control glucose synthetic medium (GSM). Meta-cleavage pathway of phenol degradation leads to formation of pyruvate and acetaldehyde. Both these end products feed as precursors for de novo triacylglycerols (TAG) biosynthesis pathway which causes accumulation of TAG in the lipid droplets (LD) of 6.12±0.78μm grown on phenol while 2.38±0.52μm observed on GSM. This was confirmed by fluorescence microscopic images of BODIPY_505-515nm stained live yeast cells. GC-MS analysis of extracted total lipid showed enhanced amount of monounsaturated fatty acid (MUFA) which was as 51.87%, 58.33% and 62.98% in presence of 0.5, 0.75 and 1g/l of phenol.

Fungal degradation of benzoic acid and related compounds

Most knowledge of the degradation of aromatic compounds has been gained through investigation of the pathways in bacteria. In recent years, however, significant developments have been made in the understanding of the degradation of these compounds in yeasts and moulds. Many similarities have been identified between the bacteria and the yeasts and moulds but some significant differences occur. This review highlights these differences and discusses the current understanding of the fungal degradation of benzoate and some substituted benzoates. The pathways for the further conversion of the ring-fission substrates, which are common to all fungi capable of degrading these aromatic compounds, are also presented.

Phenol degradation by Aureobasidium pullulans FE13 isolated from industrial effluents

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

Relationship of chemical structures of textile dyes on the pre-adaptation medium and the potentialities of their biodegradation by Phanerochaete chrysosporium

Azo dye derivatives of azobenzene constitute the largest group of dyes used in the textile industry and possess recalcitrant chemical groups, such as those of azo and sulphonic acid. Some microorganisms are able to degrade these aromatic compounds. In the present work, decolourisation of culture media containing azo dyes by the ligninolytic fungus Phanerochaete chrysosporium was achieved under nitrogen-limited conditions. The dyes used in the study are derivatives of meta- or para-aminosulphonic or aminobenzoic acids and include in their structures groups such as guaiacol or syringol, which are bioaccessible to the lignin degrading fungus P. chrysosporium. The aim of this study was to pre-adapt the microorganism to the structure of the dyes and to establish the relationships of the chemical structure of the dye present in the pre-adaptation medium with the chemical structure of the dye to be degraded. The azo dye used in the pre-adaptation medium that gave the best overall decolourisation performance was a meta-aminosulphonic acid and guaiacol derivative. The azo dye derivative of a meta-aminobenzoic acid and syringol showed a better performance in the decolourisation assays. Preliminary GC-MS studies indicated the formation of a nitroso substituted catechol metabolite, a precursor of aromatic ring cleavage, which was confirmed to occur by an enzymatic assay. The presence of this type of metabolite allows the establishment of a possible metabolic pathway towards mineralisation.

Phenol degradation by yeasts isolated from industrial effluents

Yeast strains of the genera Aureobasidium, Rhodotorula and Trichosporon were isolated from stainless steel effluents and tested for their ability to utilize phenol as the sole carbon source. Fourteen strains grew in the presence of up to 10 mm phenol. Only the strain Trichosporon sp. LE3 was able to grow in the presence of up to 20 mm phenol. An inhibitory effect was observed at concentrations higher than 11 mm, resulting in reduction of specific growth rates. Phenol degradation was a function of strain, time of incubation and initial phenol concentration. All strains exhibited activity of catechol 1,2-dioxygenase and phenol hydroxylase in free cell extracts from cells grown on phenol, suggesting that catechol was oxidized by the ortho type of ring fission. Addition of glucose and benzoate reduced the phenol consumption rate, and both substrates were used simultaneously. Glucose concentrations higher than 0.25% inhibited the induction of phenol oxidation by non-proliferating cells and inhibited phenol oxidation by pre-induced cells.

Purification and properties of 4-hydroxybenzoate 1-hydroxylase (decarboxylating), a novel flavin adenine dinucleotide-dependent monooxygenase from Candida parapsilosis CBS604

A novel flavoprotein monooxygenase, 4-hydroxybenzoate 1-hydroxylase (decarboxylating), from Candida parapsilosis CBS604 was purified to apparent homogeneity. The enzyme is induced when the yeast is grown on either 4-hydroxybenzoate, 2,4-dihydroxybenzoate, or 3,4-dihydroxybenzoate as the sole carbon source. The purified monooxygenase is a monomer of about 50 kDa containing flavin adenine dinucleotide as weakly bound cofactor. 4-Hydroxybenzoate 1-hydroxylase from C. parapsilosis catalyzes the oxidative decarboxylation of a wide range of 4-hydroxybenzoate derivatives with the stoichiometric consumption of NAD(P)H and oxygen. Optimal catalysis is reached at pH 8, with NADH being the preferred electron donor. By using (18)O2, it was confirmed that the oxygen atom inserted into the product 1,4-dihydroxybenzene is derived from molecular oxygen. 19F nuclear magnetic resonance spectroscopy revealed that the enzyme catalyzes the conversion of fluorinated 4-hydroxybenzoates to the corresponding hydroquinones. The activity of the enzyme is strongly inhibited by 3,5-dichloro-4-hydroxybenzoate, 4-hydroxy-3,5-dinitrobenzoate, and 4-hydroxyisophthalate, which are competitors with the aromatic substrate. The same type of inhibition is exhibited by chloride ions. Molecular orbital calculations show that upon deprotonation of the 4-hydroxy group, nucleophilic reactivity is located in all substrates at the C-1 position. This, and the fact that the enzyme is highly active with tetrafluoro-4-hydroxybenzoate and 4-hydroxy-3-nitrobenzoate, suggests that the phenolate forms of the substrates play an important role in catalysis. Based on the substrate specificity, a mechanism is proposed for the flavin-mediated oxidative decarboxylation of 4-hydroxybenzoate.

Biodegradation of phenols by the alga Ochromonas danica

The eukaryotic alga Ochromonas danica, a nutritionally versatile, mixotrophic chrysophyte, grew on phenol as the sole carbon source in axenic culture and removed the phenol carbon from the growth medium. Respirometric studies confirmed that the enzymes involved in phenol catabolism were inducible and that the alga oxidized phenol; the amount of oxygen consumed per mole of oxidized substrate was approximately 65% of the theoretical value. [U-14C]phenol was completely mineralized, with 65% of the 14C label appearing as 14CO2, approximately 15% remaining in the aqueous medium, and the rest accounted for in the biomass. Analysis of the biomass showed that 14C label had been incorporated into the protein, nucleic acid, and lipid fractions; phenol carbon is thus unequivocally assimilated by the alga. Phenol-grown cultures of O. danica converted phenols to the corresponding catechols, which were further metabolized by the meta-cleavage pathway. This surprising result was rigorously confirmed by taking the working stock culture through a variety of procedures to check that it was axenic and repeating the experiments with algal extracts. This is, as far as is known, the first definitive identification of the meta-cleavage pathway for aromatic ring degradation in a eukaryotic alga, though its incidence in other eukaryotes has been (infrequently) suggested.

Catabolism of benzene compounds by ascomycetous and basidiomycetous yeasts and yeastlike fungi. A literature review and an experimental approach

A literature review is given on growth of yeasts on benzene compounds and on the catabolic pathways involved. Additionally, a yeast collection was screened for assimilation of phenol and 3-hydroxybenzoic acid. Fifteen ascomycetous and thirteen basidiomycetous yeast species were selected and were tested for growth on 84 benzene compounds. It appeared that 63 of these compounds supported growth of one or more yeast species. The black yeast Exophiala jeanselmei assimilated 54 of these compounds. The catechol branch of the 3-oxoadipate pathway and its hydroxyhydroquinone variant were involved in phenol and resorcinol catabolism of ascomycetes as well as of basidiomycetes. However, these two groups of yeasts showed characteristic differences in hydroxybenzoate catabolism. In the yeastlike fungus E. jeanselmei and in basidiomycetes of the genera Cryptococcus, Leucosporidium and Rhodotorula, the protocatechuate branch of the 3-oxoadipate pathway was induced by growth on 3- and 4-hydroxybenzoic acids. In three Trichosporon species and in all ascomycetous yeasts tested, 4-hydroxybenzoic acid was catabolyzed via protocatechuate and hydroxyhydroquinone. These yeasts were unable to cleave protocatechuate. 3-Hydroxybenzoic and 3-hydroxycinnamic acids were catabolized in ascomycetous yeasts via the gentisate pathway, but in basidiomycetes via protocatechuate. Incomplete oxidation of phenol, some chlorophenols, cresols and xylenols was observed in cultures of Candida parapsilosis growing on hydroquinone. Most compounds transformed by the growing culture were also converted by the phenol monooxygenase present in cell-free extracts of this yeast. They did not support growth. The relationship between the ability of ascomycetous yeasts to assimilate n-alkanes, amines and benzene compounds, and the presence of Coenzyme Q9 is discussed.

Phenol hydroxylase from Trichosporon cutaneum: gene cloning, sequence analysis, and functional expression in Escherichia coli

A cDNA clone encoding phenol hydroxylase from the soil yeast Trichosporon cutaneum was isolated and characterized. The clone was identified by hybridization screening of a bacteriophage lambda ZAP-based cDNA library with an oligonucleotide probe which corresponded to the N-terminal amino acid sequence of the purified enzyme. The cDNA encodes a protein consisting of 664 amino acids. Amino acid sequences of a number of peptides obtained by Edman degradation of various cleavage products of the purified enzyme were identified in the cDNA-derived sequence. The phenol hydroxylase cDNA was expressed in Escherichia coli to yield high levels of active enzyme. The E. coli-derived phenol hydroxylase is very similar to the T. cutaneum enzyme with respect to the range of substrates acted upon, inhibition by excess phenol, and the order of magnitude of kinetic parameters in the overall reaction. Southern blot analysis revealed the presence of phenol hydroxylase gene-related sequences in a number of T. cutaneum and Trichosporon beigelii strains and in Cryptococcus elinovii but not in Trichosporon pullulans, Trichosporon penicillatum, or Candida tropicalis.

Molecular cloning, characterization, and regulation of a Pseudomonas pickettii PKO1 gene encoding phenol hydroxylase and expression of the gene in Pseudomonas aeruginosa PAO1c

A 26-kilobase BamHI restriction endonuclease DNA fragment was cloned from Pseudomonas pickettii PKO1, a strain isolated from a soil microcosm that had been amended with benzene, toluene, and xylene. This DNA fragment, cloned into vector plasmid pRO1727 and designated pRO1957, allowed Pseudomonas aeruginosa PAO1c to grow on phenol as the sole source of carbon. Physical and functional restriction endonuclease maps have been derived for the cloned DNA fragment. Two DNA fragments carried in trans and derived from subclones of pRO1957 show phenol hydroxylase activity in cell extracts of P. aeruginosa. Deletion and subcloning analyses of these fragments indicated that the gene encoding phenol hydroxylase is positively regulated. Phenol and m-cresol were shown to be inducers of the enzyme. o-Cresol and p-cresol did not induce enzymatic activity but could be metabolized by cells that had been previously exposed to phenol or m-cresol; moreover, the enzyme exhibited a rather broad substrate specificity and was sensitive to thiol-inhibiting reagents. A novel polypeptide with an estimated molecular mass of 80,000 daltons was detected in extracts of phenol-induced cells of P. aeruginosa carrying plasmid pRO1959.

Utilization of phenol by hydrocarbon assimilating yeasts

77 Ascomycetous, basidiomycetous as well as imperfect yeast strains of 46 different species and 20 genera were tested for growth with the substrates n-octane, n-hexadecane, and phenol. Of 59 yeast strains with ascomycetous cell wall structure 33 grew on hydrocarbons and 32 on phenol. No yeast strain out of 26 which are unable to use n-alkanes as a source of carbon and energy grew on phenol. In comparison with the latter 32 out of 33 n-hexadecane assimilating yeasts were also capable of using phenol. All n-octane utilizing yeasts of this group also assimilate phenol as a carbon source for growth. The correlation of the hydrocarbon assimilation with the phenol assimilation seems to be not so strong in the basidiomycetous yeasts. 7 out of 18 strains from this group grew on n-hexadecane and 13 on phenol. Furthermore, it could be shown that the use of hydrocarbons and phenol (as well as methanol) is strongly correlated with the coenzyme Q structure of the respective yeast strain. The results are discussed with respect to the particular chemical properties of the substrates used and the fact that coenzyme Q structure is considered to be an important marker of evolutionary relationships among yeasts.

Transport and hydrolysis of disaccharides by Trichosporon cutaneum

Trichosporon cutaneum is shown to utilize six disaccharides, cellobiose, maltose, lactose, sucrose, melibiose, and trehalose. T. cutaneum can thus be counted with the rather restricted group of yeasts (11 to 12% of all investigated) which can utilize lactose and melibiose. The half-saturation constants for uptake were 10 +/- 3 mM sucrose or lactose and 5 +/- 1 mM maltose, which is of the same order of magnitude as those reported for Saccharomyces cerevisiae. Our results indicate that maltose shares a common transport system with sucrose and that there may be some interaction between the uptake systems for lactose, cellobiose, and glucose. Lactose, cellobiose, and melibiose are hydrolyzed by cell wall-bound glycosidase(s), suggesting hydrolysis before or in connection with uptake. In contrast, maltose, sucrose, and trehalose seem to be taken up as such. The uptake of sucrose and lactose is dependent on a proton gradient across the cell membrane. In contrast, there were no indications of the involvement of gradients of H+, K+, or Na+ in the uptake of maltose. The uptake of lactose is to a large extent inducible, as is the corresponding glycosidase. Also the glycosidases for cellobiose, trehalose, and melibiose are inducible. In contrast, the uptake of sucrose and maltose and the corresponding glycosidases is constitutive.