Degradation of the γ-Carboxyl-Containing Diarylpropane Lignin Model Compound 3-(4′-Ethoxy-3′-Methoxyphenyl)-2-(4″-Methoxyphenyl)Propionic Acid by the Basidiomycete Phanerochaete chrysosporium

The white-rot basidiomycete Phanerochaete chrysosporium metabolized 3-(4′-ethoxy-3′-methoxyphenyl)-2-(4″-methoxyphenyl)propionic acid (V) in low-nitrogen, stationary cultures, conditions under which ligninolytic activity is expressed. The ability of several fungal mutant strains to degrade V reflected their ability to degrade [¹⁴C]lignin to ¹⁴CO₂. 1-(4′-Ethoxy-3′-methoxyphenyl)-2-(4″-methoxyphenyl)-2- hydroxyethane (VII), anisyl alcohol, and 4-ethoxy-3-methoxybenzyl alcohol were isolated as metabolic products, indicating an initial oxidative decarboxylation of V, followed by α, β cleavage of the intermediate (VII). Exogenously added VII was rapidly converted to anisyl alcohol and 4-ethoxy-3-methoxybenzyl alcohol. When the degradation of V was carried out under ¹⁸O₂, ¹⁸O was incorporated into the β position of the diarylethane product (VII), indicating that the reaction is oxygenative.     

Arylglycerol-gamma-Formyl Ester as an Aromatic Ring Cleavage Product of Nonphenolic beta-O-4 Lignin Substructure Model Compounds Degraded by Coriolus versicolor

4-Ethoxy-3-methoxyphenylglycerol-gamma-formyl ester (compound IV) was identified as a degradation product of both 4-ethoxy-3-methoxyphenylglycerol-beta-syringaldehyde ether (compound I) and 4-ethoxy-3-methoxyphenylglycerol-beta-2,6-dimethoxyphenyl ether (compound II) by a ligninolytic culture of Coriolus versicolor. An isotopic experiment with a C-labeled compound (compound II') indicated that the formyl group of compound IV was derived from the beta-phenoxyl group of beta-O-4 dimer as an aromatic ring cleavage fragment. However, compound IV was not formed from 4-ethoxy-3-methoxyphenylglycerol-beta-guaiacyl ether (compound III). gamma-Formyl arylglycerol (compound IV) could be a precursor of 4-ethoxy-3-methoxyphenylglycerol (compound VI), because 3-(4-ethoxy-3-methoxyphenyl)-1-formyloxy propane (compound VII) was cleaved to give 3-(4-ethoxy-3-methoxyphenyl)-1-propanol (compound VIII) by C. versicolor. 4-Ethoxy-3-methoxyphenylglycerol-beta,gamma-cyclic carbonate (compound V), previously found as a degradation product of compound III by Phanerochaete chrysosporium (T. Umezawa, and T. Higuchi, FEBS Lett., 25:123-126, 1985), was also identified from the cultures with compound I, II, and III and degraded to give the arylglycerol (compound VI). An isotopic experiment with C-labeled compounds II' and III' indicated that the carbonate carbon of compound V was derived from the beta-phenoxyl groups of beta-O-4 substructure.     

Metabolism of Radiolabeled β-Guaiacyl Ether-Linked Lignin Dimeric Compounds by Phanerochaete chrysosporium

Phanerochaete chrysosporium metabolized the radiolabeled lignin model compounds [γ-¹⁴C]guaiacylglycerol-β-guaiacyl ether and [4-methoxy-¹⁴C]veratrylglycerol-β-guaiacyl ether (VI) to ¹⁴CO₂ in stationary and in shaking cultures. ¹⁴CO₂ evolution was greater in stationary culture. ¹⁴CO₂ evolution from [γ-¹⁴C]guaiacyl-glycerol-β-guaiacyl ether and [4-methoxy-¹⁴C]veratrylglycerol-β-guaiacyl ether in stationary cultures was two- to threefold greater when 100% O₂ rather than air (21% O₂) was the gas phase above the cultures. ¹⁴CO₂ evolution from the metabolism of the substrates occurred only as the culture entered the stationary phase of growth. The presence of substrate levels of nitrogen in the medium suppressed ¹⁴CO₂ evolution from both substrates in stationary cultures. [¹⁴C]veratryl alcohol and 4-ethoxy-3-methoxybenzyl alcohol were formed as products of the metabolism of VI and 4-ethoxy-3-methoxyphenylglycerol-β-guaiacyl ether, respectively.     

Casein kinase I δ/ɛ phosphorylates topoisomerase IIα at serine-1106 and modulates DNA cleavage activity

We previously reported that phosphorylation of topoisomerase (topo) IIα at serine-1106 (Ser-1106) regulates enzyme activity and sensitivity to topo II-targeted drugs. In this study we demonstrate that phosphorylation of Ser-1106, which is flanked by acidic amino acids, is regulated in vivo by casein kinase (CK) Iδ and/or CKI, but not by CKII. The CKI inhibitors, CKI-7 and IC261, reduced Ser-1106 phosphorylation and decreased formation of etoposide-stabilized topo II–DNA cleavable complex. In contrast, the CKII inhibitor, 5,6-dichlorobenzimidazole riboside, did not affect etoposide-stabilized topo II–DNA cleavable complex formation. Since, IC261 specifically targets the Ca²⁺-regulated isozymes, CKIδ and CKI, we examined the effect of down-regulating these enzymes on Ser-1106 phosphorylation. Down-regulation of these isozymes with targeted si-RNAs led to hypophosphorylation of the Ser-1106 containing peptide. However, si-RNA-mediated down-regulation of CKIIα and α′ did not alter Ser-1106 phosphorylation. Furthermore, reduced phosphorylation of Ser-1106, observed in HRR25 (CKIδ/ homologous gene)-deleted Saccharomyces cerevisiae cells transformed with human topo IIα, was enhanced following expression of human CKI. Down-regulation of CKIδ and CKI also led to reduced formation of etoposide stabilized topo II–DNA cleavable complex. These results provide strong support for an essential role of CKIδ/ in phosphorylating Ser-1106 in human topo IIα and in regulating enzyme function.     

Microbial Reduction of 1,3-Dioxo-2-Methyl-2-(3′-Oxo-6′-Carbomethoxyhexyl)-Cyclopentane to Form 1β-Hydroxy-3-Oxo-2β-Methyl-2α-(3′-Oxo-6′-Carbomethoxy-hexyl)-Cyclopentane, an Intermediate for Steroid Total Synthesis

The rate and extent of stereoselective reduction of 1,3-dioxo-2-methyl-2-(3′-oxo-6′-carbomethoxyhexyl)-cyclopentane to form the 1β-hydroxy-2β-methyl isomer by cultures of Schizosaccharomyces pombe ATCC 2476 was dramatically increased by addition to the fermentation of certain α,β-unsaturated ketones and allyl alcohol.     

Oxidation of the erythro and threo forms of the phenolic lignin model compound 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol by laccases and model oxidants

Mixtures of equal amounts of the erythro and threo forms of the phenolic arylglycerol β-aryl ether 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol were oxidized (i) with laccases from Trametes versicolor, Agaricus bisporus, Myceliophthora thermophila and Rhus vernicifera, (ii) with laccase-mediator systems consisting of T. versicolor laccase and ABTS or HBT, and (iii) with various model oxidants including cerium(IV) ammonium nitrate (CAN), lignin peroxidase, Fenton’s reagent, and lead(IV) tetraacetate (LTA). All the laccases exhibited a similar preferential degradation of the threo form. The mediator ABTS counteracted the threo preference of laccase, but the mediator HBT did not affect it. The outer-sphere model oxidants CAN and lignin peroxidase showed a preferential degradation of the threo form. LTA and Fenton’s reagent did not exhibit any stereo-preference. The results suggest that laccases of different origin, primary structure, and redox potential behave as typical outer-sphere oxidants in their interaction with the diastereomers of the arylglycerol β-aryl ether.     

Translesion synthesis by yeast DNA polymerase ζ from templates containing lesions of ultraviolet radiation and acetylaminofluorene

In the yeast Saccharomyces cerevisiae, DNA polymerase ζ (Polζ) is required in a major lesion bypass pathway. To help understand the role of Polζ in lesion bypass, we have performed in vitro biochemical analyses of this polymerase in response to several DNA lesions. Purified yeast Polζ performed limited translesion synthesis opposite a template TT (6-4) photoproduct, incorporating A or T with similar efficiencies (and less frequently G) opposite the 3′ T, and predominantly A opposite the 5′ T. Purified yeast Polζ predominantly incorporated a G opposite an acetylaminofluorene (AAF)-adducted guanine. The lesion, however, significantly inhibited subsequent extension. Furthermore, yeast Polζ catalyzed extension DNA synthesis from primers annealed opposite the AAF-guanine and the 3′ T of the TT (6-4) photoproduct with varying efficiencies. Extension synthesis was more efficient when A or C was opposite the AAF-guanine, and when G was opposite the 3′ T of the TT (6-4) photoproduct. In contrast, the 3′ T of a cis–syn TT dimer completely blocked purified yeast Polζ, whereas the 5′ T was readily bypassed. These results support the following dual-function model of Polζ. First, Polζ catalyzes nucleotide incorporation opposite AAF-guanine and TT (6-4) photoproduct with a limited efficiency. Secondly, more efficient bypass of these lesions may require nucleotide incorporation by other DNA polymerases followed by extension DNA synthesis by Polζ.     

Microbial Transformation of β-Ionone and β-Methylionone

Aspergillus niger JTS 191 was selected from many microorganisms tested as capable of converting ionones to other compounds having aromas. The individual transformation products from β-ionone were isolated and identified by comparison with synthetically derived compounds. The major products were (R)-4-hydroxy-β-ionone and (S)-2-hydroxy-β-ionone. 2-Oxo-, 4-oxo-, 3,4-dehydro-, 2,3-dehydro-4-oxo-, 3,4-dehydro-2-oxo-, (S)-2-acetoxy-, (R)-4-acetoxy-, and 5,6-epoxy-β-ionone and 4-(2,3,6-trimethylphenyl)-but-3-en-2-one were also identified. Analogous transformation products of β-methylionone also were identified. Based on gas-liquid chromatographic analysis during the fermentation, we propose two main oxidative pathways of β-ionone. The results of this study suggest that these transformations of β-ionones may be useful as tobacco-flavoring compounds.     

Role of β-Oxidation Enzymes in γ-Decalactone Production by the Yeast Yarrowia lipolytica

Some microorganisms can transform methyl ricinoleate into γ-decalactone, a valuable aroma compound, but yields of the bioconversion are low due to (i) incomplete conversion of ricinoleate (C₁₈) to the C₁₀ precursor of γ-decalactone, (ii) accumulation of other lactones (3-hydroxy-γ-decalactone and 2- and 3-decen-4-olide), and (iii) γ-decalactone reconsumption. We evaluated acyl coenzyme A (acyl-CoA) oxidase activity (encoded by the POX1 through POX5 genes) in Yarrowia lipolytica in lactone accumulation and γ-decalactone reconsumption in POX mutants. Mutants with no acyl-CoA oxidase activity could not reconsume γ-decalactone, and mutants with a disruption of pox3, which encodes the short-chain acyl-CoA oxidase, reconsumed it more slowly. 3-Hydroxy-γ-decalactone accumulation during transformation of methyl ricinoleate suggests that, in wild-type strains, β-oxidation is controlled by 3-hydroxyacyl-CoA dehydrogenase. In mutants with low acyl-CoA oxidase activity, however, the acyl-CoA oxidase controls the β-oxidation flux. We also identified mutant strains that produced 26 times more γ-decalactone than the wild-type parents.     

Microbial Conversion of α-Ionone, α-Methylionone, and α-Isomethylionone

α-Ionone, α-methylionone, and α-isomethylionone were converted by Aspergillus niger JTS 191. The individual bioconversion products from α-ionone were isolated and identified by spectrometry and organic synthesis. The major products were cis-3-hydroxy-α-ionone, trans-3-hydroxy-α-ionone, and 3-oxo-α-ionone. 2,3-Dehydro-α-ionone, 3,4-dehydro-β-ionone, and 1-(6,6-dimethyl-2-methylene-3-cyclohexenyl)-buten-3-one were also identified. Analogous bioconversion products from α-methylionone and α-isomethylionone were also identified. From results of gas-liquid chromatographic analysis during the fermentation, we propose a metabolic pathway for α-ionones and elucidation of stereochemical features of the bioconversion.     

Bioconversion of α-Damascone by Botrytis cinerea

Bioconversion of α-damascone (compound 1) was studied with four strains of Botrytis cinerea in grape must (pH 3.2). As biotransformation products of compound 1, 3-oxo-α-damascone, cis- and trans-3-hydroxy-α-damascone, γ-damascenone, 3-oxo-8, 9-dihydro-α-damascone, and cis- and trans-3-hydroxy-8,9-dihydro-α-damascone were identified. In addition, acid-catalyzed chemical transformation of compound 1 to the diastereomers of 9-hydroxy-8,9-dihydro-α-damascone was observed. Identifications were performed by capillary gas chromatography (HRGC) and coupled HRGC techniques, i.e., on-line HRGC-mass spectrometry and HRGC-Fourier transform infrared spectroscopy, after extractive sample preparation.     

Involvement of the Terminal Oxygenase β Subunit in the Biphenyl Dioxygenase Reactivity Pattern toward Chlorobiphenyls

Biphenyl dioxygenase (BPH dox) oxidizes biphenyl on adjacent carbons to generate 2,3-dihydro-2,3-dihydroxybiphenyl in Comamonas testosteroni B-356 and in Pseudomonas sp. strain LB400. The enzyme comprises a two-subunit (α and β) iron sulfur protein (ISP_BPH), a ferredoxin (FER_BPH), and a ferredoxin reductase (RED_BPH). B-356 BPH dox preferentially catalyzes the oxidation of the double-meta-substituted congener 3,3′-dichlorobiphenyl over the double-para-substituted congener 4,4′-dichlorobiphenyl or the double-ortho-substituted congener 2,2′-dichlorobiphenyl. LB400 BPH dox shows a preference for 2,2′-dichlorobiphenyl, and in addition, unlike B-356 BPH dox, it can catalyze the oxidation of selected chlorobiphenyls such as 2,2′,5,5′-tetrachlorobiphenyl on adjacent meta-para carbons. In this work, we examine the reactivity pattern of BPH dox toward various chlorobiphenyls and its capacity to catalyze the meta-para dioxygenation of chimeric enzymes obtained by exchanging the ISP_BPH α or β subunit of strain B-356 for the corresponding subunit of strain LB400. These hybrid enzymes were purified by an affinity chromatography system as His-tagged proteins. Both types, the chimera with the α subunit of ISP_BPH of strain LB400 and the β subunit of ISP_BPH of strain B-356 (the α_LB400β_B-356 chimera) and the α_B-356β_LB400 chimera, were functional. Results with purified enzyme preparations showed for the first time that the ISP_BPH β subunit influences BPH dox’s reactivity pattern toward chlorobiphenyls. Thus, if the α subunit were the sole determinant of the enzyme reactivity pattern, the α_B-356β_LB400 chimera should have behaved like B-356 ISP_BPH; instead, its reactivity pattern toward the substrates tested was similar to that of LB400 ISP_BPH. On the other hand, the α_LB400β_B-356 chimera showed features of both B-356 and LB400 ISP_BPH where the enzyme was able to metabolize 2,2′- and 3,3′-dichlorobiphenyl and where it was able to catalyze the meta-para oxygenation of 2,2′,5,5′-tetrachlorobiphenyl.     

α- and β-Proteobacteria Control the Consumption and Release of Amino Acids on Lake Snow Aggregates

We analyzed the composition of aggregate (lake snow)-associated bacterial communities in Lake Constance from 1994 until 1996 between a depth of 25 m and the sediment surface at 110 m by fluorescent in situ hybridization with rRNA-targeted oligonucleotide probes of various specificity. In addition, we experimentally examined the turnover of dissolved amino acids and carbohydrates together with the microbial colonization of aggregates formed in rolling tanks in the lab. Generally, between 40 and more than 80% of the microbes enumerated by DAPI staining (4′,6′-diamidino-2-phenylindole) were detected as Bacteria by the probe EUB338. At a depth of 25 m, 10.5% ± 7.9% and 14.2% ± 10.2% of the DAPI cell counts were detected by probes specific for α- and β-Proteobacteria. These proportions increased to 12.0% ± 3.3% and 54.0% ± 5.9% at a depth of 50 m but decreased again at the sediment surface at 110 m to 2.7% ± 1.4% and 41.1% ± 8.4%, indicating a clear dominance of β-Proteobacteria at depths of 50 and 110 m, where aggregates have an age of 3 to 5 and 8 to 11 days, respectively. From 50 m to the sediment surface, cells detected by a Cytophaga/Flavobacteria-specific probe (CF319a) comprised increasing proportions up to 18% of the DAPI cell counts. γ-Proteobacteria always comprised minor proportions of the aggregate-associated bacterial community. Using only two probes highly specific for clusters of bacteria closely related to Sphingomonas species and Brevundimonas diminuta, we identified between 16 and 60% of the α-Proteobacteria. In addition, with three probes highly specific for close relatives of the β-Proteobacteria Duganella zoogloeoides (formerly Zoogloea ramigera), Acidovorax facilis, and Hydrogenophaga palleroni, bacteria common in activated sludge, 42 to 70% of the β-Proteobacteria were identified. In the early phase (<20 h) of 11 of the 15 experimental incubations of aggregates, dissolved amino acids were consumed by the aggregate-associated bacteria from the surrounding water. This stage was followed by a period of 1 to 3 days during which dissolved amino acids were released into the surrounding water, paralleled by an increasing dominance of β-Proteobacteria. Hence, our results show that lake snow aggregates are inhabited by a community dominated by a limited number of α- and β-Proteobacteria, which undergo a distinct succession. They successively decompose the amino acids bound in the aggregates and release substantial amounts into the surrounding water during aging and sinking.     

Exonic Sequences in the 5′ Untranslated Region of α-Tubulin mRNA Modulate trans Splicing in Trypanosoma brucei

Previous studies have identified a conserved AG dinucleotide at the 3′ splice site (3′SS) and a polypyrimidine (pPy) tract that are required for trans splicing of polycistronic pre-mRNAs in trypanosomatids. Furthermore, the pPy tract of the Trypanosoma brucei α-tubulin 3′SS region is required to specify accurate 3′-end formation of the upstream β-tubulin gene and trans splicing of the downstream α-tubulin gene. Here, we employed an in vivo cis competition assay to determine whether sequences other than those of the AG dinucleotide and the pPy tract were required for 3′SS identification. Our results indicate that a minimal α-tubulin 3′SS, from the putative branch site region to the AG dinucleotide, is not sufficient for recognition by the trans-splicing machinery and that polyadenylation is strictly dependent on downstream trans splicing. We show that efficient use of the α-tubulin 3′SS is dependent upon the presence of exon sequences. Furthermore, β-tubulin, but not actin exon sequences or unrelated plasmid sequences, can replace α-tubulin exon sequences for accurate trans-splice-site selection. Taken together, these results support a model in which the informational content required for efficient trans splicing of the α-tubulin pre-mRNA includes exon sequences which are involved in modulation of trans-splicing efficiency. Sequences that positively regulate trans splicing might be similar to cis-splicing enhancers described in other systems.     

Transformation of 2,2′-Bimorphine to the Novel Compounds 10-α-S-Monohydroxy-2,2′-Bimorphine and 10,10′-α,α′-S,S′-Dihydroxy-2,2′-Bimorphine by Cylindrocarpon didymum

Whole-cell suspensions of Cylindrocarpon didymum were observed to transform 2,2′-bimorphine to the compounds 10-α-S-monohydroxy-2,2′-bimorphine and 10,10′-α,α′-S,S′-dihydroxy-2,2′-bimorphine. Mass spectrometry and ¹H nuclear magnetic resonance spectroscopy confirmed the identities of these new morphine alkaloids.     

Potential Application of N-Carbamoyl-β-Alanine Amidohydrolase from Agrobacterium tumefaciens C58 for β-Amino Acid Production

An N-carbamoyl-β-alanine amidohydrolase of industrial interest from Agrobacterium tumefaciens C58 (βcar_At) has been characterized. βcar_At is most active at 30°C and pH 8.0 with N-carbamoyl-β-alanine as a substrate. The purified enzyme is completely inactivated by the metal-chelating agent 8-hydroxyquinoline-5-sulfonic acid (HQSA), and activity is restored by the addition of divalent metal ions, such as Mn²⁺, Ni²⁺, and Co²⁺. The native enzyme is a homodimer with a molecular mass of 90 kDa from pH 5.5 to 9.0. The enzyme has a broad substrate spectrum and hydrolyzes nonsubstituted N-carbamoyl-α-, -β-, -γ-, and -δ-amino acids, with the greatest catalytic efficiency for N-carbamoyl-β-alanine. βcar_At also recognizes substrate analogues substituted with sulfonic and phosphonic acid groups to produce the β-amino acids taurine and ciliatine, respectively. βcar_At is able to produce monosubstituted β²- and β³-amino acids, showing better catalytic efficiency (k_cat/K_m) for the production of the former. For both types of monosubstituted substrates, the enzyme hydrolyzes N-carbamoyl-β-amino acids with a short aliphatic side chain better than those with aromatic rings. These properties make βcar_At an outstanding candidate for application in the biotechnology industry.     

Kinetic Studies of β-Galactosidase Induction

The kinetics of β-galactosidase induction in E. coli ML 3 have been studied. Following addition of inducer, the rate of enzyme synthesis accelerates from the uninduced to a steady-state rate. At saturating concentration of inducer the time constant (T_c) for this process is 2.5 to 3 minutes. With decreasing inducer concentration (I), increasing time constants are observed. I/I + K′ approximates I/T_c. The steady-state rate of β-galactosidase synthesis is approximated by I²/I² + K². K′ and K have been estimated for IPTG and TMG. The kinetics of β-galactosidase production after the removal of inducer by dilution or after the addition of glucose have been investigated. A transition time of 2.5 to 3 minutes is observed before enzyme synthesis slows or stops. These results are consistent with the hypothesis that the enzyme-forming unit is unstable.     

Metabolism of a Non-phenolic β-O-4 Lignin Substructure Model Compound by Coriolus versicolor

A non-phenolic β-O-4 lignin substructure model, 4-ethoxy-3-methoxyphenylglycerol-β-syringaldehyde ether (I), was metabolized by a ligninolytic culture of Coriolus versicolor. Based on the identification of the metabolic products (II~XI), the following reactions were found to occur in the culture; a) oxidation (III) and reduction (II) at the benzyl (Cα′) position of the substrate (I), b) β-ether cleavage to give arylglycerols (IV, V), and c) Cα-Cβ cleavage of the arylglycerols and/or arylglycerol moiety of the substrate (I). In addition, β-deoxy diol (VI) and γ-formylglycerol (VII) were obtained as degradation products from substrate (I).     

Induction of γδT cells from HSC‐enriched BMCs co‐cultured with iPSC‐derived thymic epithelial cells

T cells bearing γδ antigen receptors have been investigated as potential treatments for several diseases, including malignant tumours. However, the clinical application of γδT cells has been hampered by their relatively low abundance in vivo and the technical difficulty of inducing their differentiation from hematopoietic stem cells (HSCs) in vitro. Here, we describe a novel method for generating mouse γδT cells by co‐culturing HSC‐enriched bone marrow cells (HSC‐eBMCs) with induced thymic epithelial cells (iTECs) derived from induced pluripotent stem cells (iPSCs). We used BMCs from CD45.1 congenic C57BL/6 mice to distinguish them from iPSCs, which expressed CD45.2. We showed that HSC‐eBMCs and iTECs cultured with IL‐2 + IL‐7 for up to 21 days induced CD45.1⁺ γδT cells that expressed a broad repertoire of Vγ and Vδ T‐cell receptors. Notably, the induced lymphocytes contained few or no αβT cells, NK1.1⁺ natural killer cells, or B220⁺ B cells. Adoptive transfer of the induced γδT cells to leukemia‐bearing mice significantly reduced tumour growth and prolonged mouse survival with no obvious side effects, such as tumorigenesis and autoimmune diseases. This new method suggests that it could also be used to produce human γδT cells for clinical applications.     

Stereo- and Regioselective Hydroxylation of α-Ionone by Streptomyces Strains

A total of 215 Streptomyces strains were screened for their capacity to regio- and stereoselectively hydroxylate β- and/or α-ionone to the respective 3-hydroxy derivatives. With β-ionone as the substrate, 15 strains showed little conversion to 4-hydroxy- and none showed conversion to the 3-hydroxy product as desired. Among these 15 Streptomyces strains, S. fradiae Tü 27, S. arenae Tü 495, S. griseus ATCC 13273, S. violaceoniger Tü 38, and S. antibioticus Tü 4 and Tü 46 converted α-ionone to 3-hydroxy-α-ionone with significantly higher hydroxylation activity compared to that of β-ionone. Hydroxylation of racemic α-ionone [(6R)-(−)/(6S)-(+)] resulted in the exclusive formation of only the two enantiomers (3R,6R)- and (3S,6S)-hydroxy-α-ionone. Thus, the enzymatic hydroxylation of α-ionone by the Streptomyces strains tested proceeds with both high regio- and stereoselectivity.