Characterisation of a degradative plasmid inPseudomonas putidathat controls the expression of 2,4-xylenol degradative genes

Pseudomonas putida as a platform for medium-chain length α,ω-diol production: Opportunities and challenges

Medium-chain-length α,ω-diols (mcl-diols) play an important role in polymer production, traditionally depending on energy-intensive chemical processes. Microbial cell factories offer an alternative, but conventional strains like Escherichia coli and Saccharomyces cerevisiae face challenges in mcl-diol production due to the toxicity of intermediates such as alcohols and acids. Metabolic engineering and synthetic biology enable the engineering of non-model strains for such purposes with P. putida emerging as a promising microbial platform. This study reviews the advancement in diol production using P. putida and proposes a four-module approach for the sustainable production of diols. Despite progress, challenges persist, and this study discusses current obstacles and future opportunities for leveraging P. putida as a microbial cell factory for mcl-diol production. Furthermore, this study highlights the potential of using P. putida as an efficient chassis for diol synthesis.

The catabolism of 2,4-xylenol and p-cresol share the enzymes for the oxidation of para-methyl group in Pseudomonas putida NCIMB 9866

Pseudomonas putida NCIMB 9866 utilizes p-cresol or 2,4-xylenol as a sole carbon and energy source. Enzymes catalyzing the oxidation of the para-methyl group of p-cresol have been studied in detail. However, those responsible for the oxidation of the para-methyl group in 2,4-xylenol catabolism are still not reported. In this study, real-time quantitative PCR analysis indicated pchC- and pchF-encoded p-cresol methylhydroxylase (PCMH) and pchA-encoded p-hydroxybenzaldehyde dehydrogenase (PHBDD) in p-cresol catabolism were also likely involved in the catabolism of 2,4-xylenol. Enzyme activity assays and intermediate identification indicated that the PCMH and PHBDD catalyzed the oxidations of 2,4-xylenol to 4-hydroxy-3-methylbenzaldehyde and 4-hydroxy-3-methylbenzaldehyde to 4-hydroxy-3-methylbenzoic acid, respectively. Furthermore, the PCMH-encoding gene pchF was found to be necessary for the catabolism of 2,4-xylenol, whereas the PHBDD-encoding gene pchA was not essential for the catabolism by gene knockout and complementation. Analyses of the maximum specific growth rate (μ m) and specific activity of the gene-knockout strain to different intermediates revealed the presence of other enzyme(s) with PHBDD activity in strain 9866. However, PHBDD played a major role in the catabolism of 2,4-xylenol in contrast to the other enzyme(s).

Cloning, sequencing, and expression of the structural genes for the cytochrome and flavoprotein subunits of p-cresol methylhydroxylase from two strains of Pseudomonas putida

The structural genes for the flavoprotein subunit and cytochrome c subunit of p-cresol (4-methylphenol) methylhydroxylase (PCMH) from Pseudomonas putida NCIMB 9869 (National Collection of Industrial and Marine Bacteria, Aberdeen, Scotland) and P. putida NCIMB 9866 were cloned and sequenced. The genes from P.putida NCIMB 9869 were for the plasmid-encoded A form of PCMH, and the genes from P.putida NCIMB 9866 were also plasmid encoded. The nucleotide sequences of the two flavoprotein genes from P.putida NCIMB 9869 and P.putida NCIMB 9866 (pchF69A and pchF66, respectively) were the same except for 5 bases out of 1,584, and the translated amino acid sequences were identical. The nucleotide sequences of the genes for the cytochrome subunits of PCMH from the two bacteria (pchC69A and pchC66) varied by a single nucleotide in their 303-base sequences, and the translated amino acid sequences differed by a single residue at position 41 (Asp in PchC69A and Ala in PchC66). Both cytochromes had 21-residue signal sequences, as expected for periplasmic proteins, and these sequences were identical. On the other hand, no signal sequences were found for the flavoproteins.pchF69A and pchC69A were expressed, separately or together, in Escherichia coli JM109 and P.putida RA4007, with active PCMH produced in both bacteria. The E. coli-expressed flavocytochrome was purified. Our studies indicated that the E.coli-expressed subunits were identical to the subunits expressed in P.putida NCIMB 9869: molecular weights, isoelectric points, UV-visible spectra, and steady-state kinetic parameters were the same for the two sets of proteins. The subunits readily associated upon mixing two crude extracts of E.coli, one extract containing PchC69A and the other containing PchF69A. The courses of association of PchC69A and PchF69A were essentially identical for pure E. coli-expressed subunits and pure P. putida 9869-expressed subunits. E. coli-expressed PchC69A and PchF69A contained covalently bound heme and covalently bound flavin adenine dinucleotide, respectively, as the proteins expressed in nature.