Transformation of the Pseudonocardiaceae amycolatopsis sp. strain HR167 is highly dependent on the physiological state of the cells

The Pseudonocardiaceae Amycolatopsis sp. strain HR167 is used in a biotransformation process to produce vanillin from ferulic acid. To make this strain accessible for genetic engineering, a direct mycelium transformation system developed for Amycolatopsis mediterranei [Madon and Hotter (1991) J Bacteriol 173: 6325-6331] was applied and optimized for Amycolatopsis sp. strain HR167. The physiological state of the cells had a major influence on the transformation rate. The highest transformation rate of about 7x10(5) transformants per microgram of DNA was obtained with mycelium harvested 6.5-7.5 h after the culture has reached the stationary growth phase. When cells were harvested outside of this time slot, the transformation rate drastically decreased. The density of the mycelium suspensions used in the transformation mixture and the methylation state of the plasmid DNA used for the transformation were also crucial parameters. With plasmid DNA isolated from Escherichia coli ET12567, transformation rates were 3,500-fold higher than those obtained with DNA isolated from E. coli XL1-Blue.

Identification of Amycolatopsis sp. strain HR167 genes, involved in the bioconversion of ferulic acid to vanillin

The gene loci ech, encoding enoyl-CoA hydratase/aldolase, and fcs, encoding an unusual feruloyl-CoA synthetase, which are involved in the bioconversion of ferulic acid to vanillin by the gram-positive bacterium Amycolatopsis sp. strain HR167, were localized on a 4,000 bp PstI fragment (P40). The nucleotide sequence of P40 was determined, revealing open reading frames of 864 bp and 1,476 bp, representing ech and fcs, respectively. The deduced amino acid sequences of ech exhibited 62% amino acid identity to the enoyl-CoA hydratase/aldolase from Pseudomonas sp. strain HR199 and the enoyl-CoA hydratase/lyase from P. fluorescens strain AN103. The deduced amino acid sequences of fcs exhibited up to 37% amino acid identity to long-chain fatty acid coenzymeA ligases but no significant similarity to the feruloyl-CoA synthetase of Pseudomonas sp. strain HR199. Fragment P40 was cloned in pBluescript SK- and fcs and ech were expressed in Escherichia coli. Recombinant strains were able to transform ferulic acid to vanillin. In crude extracts of these recombinant strains, feruloyl-CoA synthetase and enoyl-CoA hydratase/aldolase activities were detected by photometric assay and high-performance liquid chromatography. The obtained data suggest that ferulic acid degradation in the gram-positive Amycolatopsis sp. strain HR167 proceeds via a pathway similar to that recently described for the gram-negative P. fluorescens strain AN103 and Pseudomonas sp. strain HR199.

Purification and characterization of the coniferyl aldehyde dehydrogenase from Pseudomonas sp. Strain HR199 and molecular characterization of the gene

The coniferyl aldehyde dehydrogenase (CALDH) of Pseudomonas sp. strain HR199 (DSM7063), which catalyzes the NAD+-dependent oxidation of coniferyl aldehyde to ferulic acid and which is induced during growth with eugenol as the carbon source, was purified and characterized. The native protein exhibited an apparent molecular mass of 86,000 +/- 5,000 Da, and the subunit mass was 49.5 +/- 2.5 kDa, indicating an alpha2 structure of the native enzyme. The optimal oxidation of coniferyl aldehyde to ferulic acid was obtained at a pH of 8.8 and a temperature of 26 degreesC. The Km values for coniferyl aldehyde and NAD+ were about 7 to 12 microM and 334 microM, respectively. The enzyme also accepted other aromatic aldehydes as substrates, whereas aliphatic aldehydes were not accepted. The NH2-terminal amino acid sequence of CALDH was determined in order to clone the encoding gene (calB). The corresponding nucleotide sequence was localized on a 9.4-kbp EcoRI fragment (E94), which was subcloned from a Pseudomonas sp. strain HR199 genomic library in the cosmid pVK100. The partial sequencing of this fragment revealed an open reading frame of 1,446 bp encoding a protein with a relative molecular weight of 51,822. The deduced amino acid sequence, which is reported for the first time for a structural gene of a CALDH, exhibited up to 38.5% amino acid identity (60% similarity) to NAD+-dependent aldehyde dehydrogenases from different sources.