In this study, we used the non-carotenogenic yeast Pichia pastoris X33 as a receptor for β-carotene-encoding genes, in order to obtain new recombinant strains capable of producing different carotenoidic compounds. We designed and constructed two plasmids, pGAPZA-EBI* and pGAPZA-EBI*L*, containing the genes encoding lycopene and β-carotene, respectively. Plasmid pGAPZA-EBI*, expresses three genes, crtE, crtB, and crtI*, that encode three carotenogenic enzymes, geranylgeranyl diphosphate synthase, phytoene synthase, and phytoene desaturase, respectively. The other plasmid, pGAPZA-EBI*L*, carried not only the three genes above mentioned, but also the crtL* gene, that encodes lycopene β-cyclase. The genes crtE, crtB, and crtI were obtained from Erwinia uredovora, whereas crtL* was cloned from Ficus carica (JF279547). The plasmids were integrated into P. pastoris genomic DNA, and the resulting clones Pp-EBI and Pp-EBIL were selected for either lycopene or β-carotene production and purification, respectively. Cells of these strains were investigated for their carotenoid contents in YPD media. These carotenoids produced by the recombinant P. pastoris clones were qualitatively and quantitatively analyzed by high-resolution liquid chromatography, coupled to photodiode array detector. These analyses confirmed that the recombinant P. pastoris clones indeed produced either lycopene or β-carotene, according to the integrated vector, and productions of 1.141 μg of lycopene and 339 μg of β-carotene per gram of cells (dry weight) were achieved. To the best of our knowledge, this is the first time that P. pastoris has been genetically manipulated to produce β-carotene, thus providing an alternative source for large-scale biosynthesis of carotenoids.

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In this study, we used the yeast carotenogenic producer Pichia pastoris Pp-EBIL strain, which has been metabolically engineered, by heterologously expressing β-carotene-pathway enzymes to produce β-carotene, as a vessel for recombinant astaxanthin expression. For this purpose, we designed new P. pastoris recombinant-strains harboring astaxanthin-encoding genes from carotenogenic microorganism, and thus capable of producing xanthophyllic compounds. We designed and constructed a plasmid (pGAPZA-WZ) containing both the β-carotene ketolase (crtW) and β-carotene hydroxylase (crtZ) genes from Agrobacterium aurantiacum, under the control of the GAP promoter and containing an AOX-1 terminator. The plasmid was then integrated into the P. pastoris Pp-EBIL strain genomic DNA, producing clone Pp-EBILWZ. The recombinant P. pastoris (Pp-EBILWZ) cells exhibited a strong reddish carotenoid coloration and were confirmed, by HPLC, to produce not only the previous described carotenoids lycopene and β-carotene, but also de novo synthesized astaxanthin.

The gammaproteobacterium Pseudomonas syringae pv. tomato DC3000 is the causal agent of bacterial speck, a common disease of tomato. The mode of infection of this pathogen is not well understood, but according to molecular biological, genomic and proteomic data it produces a number of proteins that may promote infection and draw nutrients from the plant. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a major enzyme of carbon metabolism that was reported to be a surface antigen and virulence factor in other pathogenic microorganisms, but its possible role in the infection process of P. syringae has so far not been studied. Whole-genome sequence analyses revealed the occurrence in this phytopathogenic bacterium of three paralogous gap genes encoding distinct GAPDHs, namely two class I enzymes having different molecular mass subunits and one class III bifunctional D-erythrose-4-phosphate dehydrogenase/GAPDH enzyme. By using genome bioinformatics data, as well as alignments of both DNA and deduced protein sequences, the three gap genes of P. syringae were one-step cloned with a His-Tag in pET21a vector using a PCR-based strategy, and its expression optimized in Escherichia coli BL21 to achieve high yield of the heterologous proteins. In accordance with their distinct molecular phylogenies, these bacterial gap genes encode functional GAPDHs of diverse molecular masses and nicotinamide-coenzyme specificities, suggesting specific metabolic and/or cellular roles.