Development of a Transgenic Flammulina velutipes Oral Vaccine for Hepatitis B.

Orally administered fungal vaccines show promise for the prevention of infectious diseases. Edible mushrooms are deemed appropriate hosts to produce oral vaccines due to their low production cost and low risk of gene contamination. However, their low expression level of antigens has limited the potential development of oral vaccines using mushrooms. The low expression level might result from impurity of the transgenic mycelia since dikaryotic mycelia are commonly used as transformation materials. In this study, stable transgenic hepatitis B virus surface antigen (HBsAg) in Flammulina velutipes transformants was obtained by Agrobacterium-mediated transformation, followed by fruiting and basidiospore mating. The formation of HBsAg was detected by western blot analysis. The expression levels of HBsAg in transgenic F. velutipes fruiting bodies were (129.3±15.1), (110.9±1.7) and (161.1±8.5) ng/g total soluble protein. However, the values may be underestimated due to incomplete protein extraction. Two of the four pigs in the experimental group produced positive anti-HBsAg-specific IgG after being fed the HBsAg transgenic F. velutipes fruiting bodies for 20 weeks, while no anti-HBsAg antibody was detected in the control group. One of the positive pigs had HBsAg titres of 5.36 and 14.9 mIU/mL in weeks 10 and 14, respectively, but expression faded thereafter. The other positive pig displayed HBsAg titres of 9.75, 17.86 and 39.87 mIU/mL in weeks 14, 18 and 20, respectively. The successful immunogenicity in pigs fed transgenic F. velutipes fruiting bodies demonstrated the potential of using the fungus as an oral vaccine.

Metabolic engineering probiotic yeast produces 3S, 3'S-astaxanthin to inhibit B16F10 metastasis.

3S, 3'S-Astaxanthin is the most powerful antioxidant to scavenge free radicals in the world. In this study, a 3S, 3'S-astaxanthin biosynthesis pathway was constructed in a probiotic yeast, Kluveromyces marxianus, denoted YEAST, and its bioactive metabolites were extracted for biofunctional assessments. The bio-safety examination was achieved by two animal models as following: First, no significant toxic effects on YEAST groups were found in zebrafish; Second, after feeding YEAST for 4 weeks, the rat-groups showed no visible abnormality, and no significant change of the body weight and blood biochemistry tests. The inhibition of lung metastasis of melanoma cells and the increment of the survival rate were demonstrated by feeding YEAST and injecting the intravenous commercial astaxanthin in vivo rodent model. Based on in vitro assays of 1,1-diphenyl-2-picryl-hydrazyl (DPPH) scavenging analysis, ferrous ion chelating ability, reducing power assessment, and mushroom tyrosinase inhibition evaluation, YEAST-astaxanthin showed anti-oxidative and tyrosinase suppressive properties. Taken together, the 3S, 3'S-astaxanthin producing probiotic yeast is safe to be used in the bio-synthesis of functional and pharmaceutical compounds, which have broad industrial applications on cosmetic, food and feed additive and healthcare.

Metabolic engineering a yeast to produce astaxanthin.

In this study, an astaxanthin-biosynthesis Kluyveromyces marxianus strain Sm23 was first constructed, which could produce 31µg/g DCW astaxanthin. Then, repeated genome integration of the key astaxanthin biosynthesis genes Hpchyb and bkt was done to increase gene copy number and astaxanthin yield. Four improved strains were obtained and the yield of astaxanthin and the total yield of carotenoids in a strain increased with the copy numbers of Hpchyb and bkt. To improve the yield further, the gene Hpchyb from Haematococcus pluvialis was modified by site-directed mutagenesis to increase the enzyme efficiency or/and to prevent the heterologous protein degradation by ubiquitination. Using repeated-integration approach of bkt and the mutated Hpchyb into Sm23, the S3-2 strain was obtained and shown to produce the 3S, 3'S-astaxanthin at 9972µg/g DCW in a 5L fermentor.

Integrating an algal ß-carotene hydroxylase gene into a designed carotenoid-biosynthesis pathway increases carotenoid production in yeast.

The algal ß-carotene hydroxylase gene Crchyb from Chlamydomonas reinhardtii, Czchyb from Chlorella zofingiensis, or Hpchyb from Haematococcus pluvialis and six other carotenoid-synthesis pathway genes were co-integrated into the genome of a yeast host. Each of these three algal genes showed a higher efficiency to convert ß-carotene to downstream carotenoids than the fungal genes from Phaffia rhodozyma. Furthermore, the strain with Hpchyb displayed a higher carotenoid productivity than the strains integrated with Crchyb or Czchyb, indicating that Hpchyb is more efficient than Crchyb and Czchyb. These results suggest that ß-carotene hydroxylase plays a crucial role in the biosynthesis of carotenoids.