Improving ergosterol production from molasses by Saccharomyces cerevisiae / 生物工程学报

Ergosterol is an economically important metabolite produced by yeast. To improve the production of ergosterol by Saccharomyces cerevisiae YEH56 (pHXA42) from molasses, a cheap and regenerative material, different strategies were applied. First, Plackett-Burman design and central composite design were applied to screen the significant factors in fermentation medium using ergosterol yield (g/L) as the response value. Ergosterol yield reached 371.56 mg/L by using the optimal fermentation medium in shake-flask culture (total sugar in molasses 40 g/L, KH2PO4 1 g/L, K2HPO4 1.86 g/L, CuSO4 x 5H2O 17.5 mg/L, FeSO4 x 7H2O 13.9 mg/L, MgSO4 x 5H2O 12.3 mg/L, corn steep liquor 10 mL/L), which was increased by 29.5% compared with the initial culture. Second, ergosterol yield was increased by 62.1% using a pH-control strategy in a 5-L bioreactor. Third, ergosterol production was improved further by using molasses feeding strategy. After 38 h fermentation, ergosterol yield reached 1 953.85 mg/L, which was 3.2 times of that in batch fermentation. Meanwhile, ergosterol production rate was increased by 42.7% compared with that in the batch culture.

Diversity and genetic stability of yeast flocculation caused by variation of tandem repeats in yeast flocculin genes / 生物工程学报

Yeast flocculation is described as a reversible, asexual and calcium dependent process, in which cells adhere to form flocs by interaction of specific cell surface proteins named flocculins on yeast cells with mannose residues present on the cell wall of adjacent yeast cells. Yeast flocculation provides a very economical and convenient pathway for separation of yeast cells from the fermentation broth or removal of heavy metal ions from effluent. A large number of tandem repeats have been found in genes encoding flocculins, which not only have great regulatory effect on the structure and function of flocculins, generating the diversity of flocculation characteristics, but lead to genetic instability in flocculation as well for driving slippage and recombination reactions within and between FLO genes. Here, the research progress in effect of variation of tandem repeats in FLO genes on flocculation characteristics and genetic stability were reviewed to direct and promote the controllable application of flocculation in industrial fermentation process and environmental remediation.

Effect of Serum from Maintenance Hemodialysis Patients on Expression of ICAM-1 in Human Umbilical Vein Endothelial Cells / 天津医药

Objective: To study the effect of serum from maintenance hemodialysis(MHD) patients on the expression of intercellular adhesion molecule-1(ICAM-1) in human umbilical vein endothelial cells(HUVEC) cultured in vitro, and the mechanism of endothelial cells dysfunction caused by serum from MHD patients thereof. Methods: HUVEC were incubated for 1 h, 3 h, 6 h and 12 h in RPMI 1640 culture media containing 10 % fetal cattle serum(FCS )(group A), 10% normal human serum (group B) and 10% MHD patient serum (group C) respectively. The immunocytochemical method was used to determine the expression of ICAM-1. Results: There were significant differences in the expression of ICAM-1 in HUVEC among stimulation groups with different serums(P < 0.05). Compared with groups A and B, the expression of ICAM-1 was significantly increased in HUVEC of group C. There was significant difference in the expression of ICAM-1 at the different stimulation times(P < 0.05). There was significant interaction between the expression of ICAM-1 in HUVEC and stimulation groups with different serum and the stimulation times(P < 0.05). Conclusion: The serum from MHD patients with chronic renal failure can promote the expression of ICAM-1 in HUVEC cultured in vitro, thus causing the dysfunction of endothelial cell.

Optimized expression of the L1 protein of human papillomavirus in Hansenula polymorpha / 生物工程学报

The heterologously expressed L1 protein of human papilomavirus 16 can assembly into virus-like particles (VLPs), which has been used as prophylactic vaccine for cervical carcinoma. To express L1 protein in Hansenula polymorpha, we analyzed the codon usage of the native gene of L1 protein and redesigned the encoding sequence according to the codon bias of H. polymorpha. We used assembly PCR to synthesize the native gene HPV16L1-N and the codon optimized gene HPV16L1. The synthesized genes were cloned into pMOXZa-A vector to generate plasmids pMOXZ-HPV16N and pMOXZ-HPV16. The expression cassettes MOXp-HPV16L1(N)-AOXTT were cloned into YEp352 vector and transferred into H. polymorpha. After methanol inducement, the expression of L1 protein in H. polymorpha was detected from the codon optimized gene HPV16L1 rather than the native gene HPVI6L1-N. The parameters for induced cultivation for strain HP-U-16L with HPV16L1 were investigated in shaking flask cultures. After induced cultivation in YPM (pH 7.0) medium supplemented with methanol to a final concentration of 1.0% every 12 h at 37 degrees C for 72 h, the recombinant produced 78.6 mg/L of L1 protein. This work offers the possibility for the production of prophylactic vaccine for cervical carcinoma by H. polymorpha.