High-throughput screening of Saccharomyces cerevisiae efficiently producing tyrosine / 生物工程学报

Tyrosine is an important aromatic amino acid. Besides its nutritional value, tyrosine is also an important precursor for the synthesis of coumarins and flavonoids. Previously, our laboratory constructed a Saccharomyces cerevisiae strain LTH0 (ARO4K229L, ARO7G141S, Δaro10, Δzwf1, Δura3) where tyrosine feedback inhibition was released. In the present study, heterologous expression of betaxanthins synthesis genes DOD (from Mirabilis jalapa) and CYP76AD1 (from sugar beet B. vulgaris) in strain LTH0 enabled production of yellow fluorescence. The engineered strain LTH0-DOD-CYP76AD1 was subjected to UV combined with ARTP mutagenesis, followed by flow cytometry screening. Among the mutants screened, the fluorescence intensity of the mutant strain LTH2-5-DOD-CYP76AD1 at the excitation wavelength of 485 nm and emission wavelength of 505 nm was (5 941±435) AU/OD, which was 8.37 times higher than that of strain LTH0-DOD-CYP76AD1. Fourteen mutant strains were subjected to fermentation to evaluate their tyrosine producing ability. The highest extracellular tyrosine titer reached 26.8 mg/L, which was 3.96 times higher than that of strain LTH0-DOD-CYP76AD1. Heterologous expression of the tyrosine ammonia lyase FjTAL derived from Flavobacterium johnsoniae further increased the titer of coumaric acid to 119.8 mg/L, which was 1.02 times higher than that of the original strain LTH0-FjTAL.

Construction of a highly efficient synthetic lycopene engineered Saccharomyces cerevisiae / 生物工程学报

Lycopene, as a high value-added terpene compound, has been widely concerned by researchers at home and abroad. Firstly, the ability of lycopene synthesis of Saccharomyces cerevisiae model strains S288c and YPH499 was analyzed and compared. The results showed that YPH499 was more suitable for lycopene synthesis as yeast chassis. Subsequently, the effects of constitutive promoters GPDpr, TEF1pr and inducible promoters GAL1pr, GAL10pr on Lycopene synthesis were compared. The results showed that when GPDpr and TEF1pr were used as promoters of crtE, crtB and crtI in lycopene synthesis pathway, the production of lycopene was 15.31 mg/L after 60 h fermentation in shaking flask. When GAL1pr and GAL10pr were used as promoters, the production was 123.89 mg/L, which was 8.09 times higher. In addition, the methylvaleric acid (MVA) pathway was further modified to overexpress the key enzyme gene of N-terminal truncation, tHMG1 (3-hydroxy-3-methylglutaryl coenzyme A reductase). The lycopene production was 265.68 mg/L, and the yield per cell was 72.79 mg/g. The Saccharomyces cerevisiae strain designed and constructed in this study can express lycopene in high yield per cell, thus could be used in the industrial production of lycopene after further construction and optimization.

Development and verification of an FLP/FRT system for gene editing in Bacillus licheniformis / 生物工程学报

Few tools of gene editing have been developed in Bacillus licheniformis at present. In order to enrich the tools, an FLP/FRT gene editing system that can repeatedly use a single selectable marker was constructed in Bacillus licheniformis, and the system was verified by knocking out an alpha amylase gene (amyL), an protease gene (aprE) and knocking in an exogenous Vitreoscilla hemoglobin gene (vgb). First, knock-out plasmids pNZTT-AFKF of amyL and pNZTT-EFKF of aprE were constructed using thermosensitive plasmid pNZT1 as a carrier. The two knock-out plasmids contained respective homology arms, resistance genes and FRT sites. Then the knock-out plasmids were transformed into Bacillus licheniformis and the target genes were replaced by respective deletion cassette via twice homologous exchange. Finally, an expression plasmid containing FLP recombinase reading frane was introduced and mediated the excision of resistance marker. In order to expand the practicability of the system, knock-in plasmid pNZTK-PFTF-vgb was constructed, with which knock-in of vgb at pflB site was carried out successfully. The results showed that amyL and aprE were successfully knocked out and the marker kanamycin cassette exactly excised. The activities of amylase and protease of deletion mutants were reduced by 95.3% and 80.4% respectively. vgb was successfully knocked in at pflB site and the marker tetracycline cassette excised. The expression of integrated vgb was verified via real-time PCR. It is the first time to construct an FLP/FRT system for gene editing in Bacillus licheniformis, which could provide an effective technical means for genetic modification.

Relationship between mycelium morphology and laccase production of Pleurotus ferulae in submerged cultivation / 生物工程学报

In this study, the relationship between mycelium morphology and laccase production was studied. The results indicated that the morphology of P. ferulae pellets was changed when glass beads were added. Laccase production showed higher with spherical mycelium than with filamentous or flocculent mycelium. In addition, the spherical mycelium with a diameter of 0.2-0.4 mm highly affected laccase production. Effect of the composition of culture medium on pellets was investigated and results indicated that various concentrations of glucose, corn meal and wheat bran were important to the formation of pellets in diameter of 0.2-0.4 mm. Besides nutrients, the addition of non-nutritional substrates influenced the distribution of P. ferulae pellets. However, the production of laccase was not promoted by non-nutritional substrates.

Cloning, expression of phospholipase A1 from Serratia liquefaciens and auto-induction fermentation by lactose / 生物工程学报

To produce recombinant phospholipase A(1) (PLA(1)) by Escherichian coli, the pla gene encoding PLA(1) was amplified from Serratia liquefaciens by PCR and cloned into two vectors pET20-b(+) and pET28-a(+). The two recombinant plasmids were then transformed into E. coli BL21 (DE3) individually to express PLA(1). E. coli BL21(DE3)/pET28a-pla yielded extracellular PLA(1) with an activity of 40.8 U/mL in batch cultivations of shaken flasks by auto-induction, which was accounted for 91% of total enzyme activity. On the basis of primal auto-induction medium, the optimized fermentation medium of PLA(1) contained tryptone 10 g/L, yeast extract 5 g/L, glucose 0.8 g/L, lactose 5 g/L, Na2HPO4 25 mmol/L, KH2PO4 25 mmol/L and 1 mmol/L MgSO4 (final concentration). Glycine (7.5 g/L) was added 6 h after inoculated. After incubated at 37 degrees C for 24 h, extracellular enzyme activity reached 128.7 U/mL.