Effect of CCH1 or MID1 gene disruption on drug tolerance and pathogenesis of Candida albicans / 生物工程学报

The calcium gate encoded by CCH1 and MID1 genes is the main channel for external calcium absorption. As one of the important secondary messengers, the elevation of calcium concentration could activate some pathways to take part in various cell processes. In this study, we used CCH1 and MID1 mutant strains and also constructed their complementary strains to study the effect of drug tolerance and virulence of Candida albicans after CCH1 or MID1 deletion. By drug plate sensitivity assay and the broth microdilution method, we compared the changes between different strains. Moreover, we added calcium channel blocker and inhibitors to analyze the effect of calcium concentration on drug action. After the deletion of CCH1 or MID1 gene, the strain exhibited an obvious sensitivity to FLUC and ITRA, and the drug action was regulated by the calcium concentration. In a mouse model of intravenous infection, we found that attenuated virulence of cch1delta/delta or mid1delta/delta strain is specifically due to a loss of CCH1 or MID1 gene.

Effect of CCH1 and MID1 in calcium influx under alkaline pH and its regulation by Crz1p transcription factor in Candida albicans / 生物工程学报

In Candida albicans, adaptation to environmental pH is relevant to its pathogenicity. Calcium signaling pathway involves in many stress responses and often accompany with Ca2+ fluctuation. We constructed CCH1 and MID1 mutant strains and studied their effect on calcium influx and further investigated the regulation by Crz1p transcription factor. We used PCR-directed gene disruption to construct cch1delta/delta and mid1delta/delta null mutant. By using a flow cytometry-based method we monitored the free cytosolic Ca2+ levels under alkaline stress. Moreover, we constructed pPHO89-LacZ plasmids and by beta-Galactosidase assays, we analyzed the changes of LacZ activities after gene disruption. The results showed that alkaline stress induced calcium burst reduced obviously in cch1delta/delta and mid1delta/delta mutant strains, also for LacZ activities, and fully abolished in crz1delta/delta mutant strain. Finally, by realtime PCR, we confirmed the regulation role of Crz1p in CCH1 and MID1 genes but in a calcineurin independent way. Studies on the effect of calcium pathway on response to alkaline stress will provide an important theoretical basis for Candida albicans infection-oriented treatment and new drug targets.

Cloning of delta8-fatty acid desaturase gene from Euglena gracilis and its expression in Saccharomyces cerevisiae / 生物工程学报

Delta8 desaturase pathway, different from common delta6 desaturase pathway, is an alternate pathway of polyunsaturated fatty acids biosynthesis. Delta8-fatty acid desaturase is one of the key enzymes in delta8 desaturase pathway. Two specific fragments were separately cloned from genomic DNA and cDNA of Euglena gracilis by PCR with the primers designed according to the reported sequence. Comparison of the genomic and cDNA sequences revealed that there wasn't intron in this delta8-fatty acid desaturase gene. This gene has an open reading frame of 1 266 bp that encodes 421 amino acids. It is 6 bp longer than the reported gene sequence, and also showed certain difference from the reported sequence in the N-terminal. The recombinant expression plasmid pYEFD by subcloning delta8-fatty acid desaturase gene into the yeast-E. coli shuttle vector pYES2.0 was constructed and was transformed into the defective mutant INVSc1 of Saccharomyces cerevisiae by electrotransformation. The resulting strain YD8 harboring plasmid pYEFD was selected and was cultured in the induction medium with exogenous substrates omega6-eicosadienoic acid and omega3-eicosatrienoic acid for the expression of delta8-fatty acid desaturase gene. The results indicated that high level expressed As-fatty acid desaturase could convert omega6-eicosadienoic acid and omega3-eicosatrienoic acid to dihomo-gamma-linolenic acid and eicosatetraenoic acid with substrate conversion ratio 31.2% and 46.3%, respectively.

Cloning, expression and functional analysis of the genes in TPS/TPP trehalose synthetic pathway of Meiothermus ruber / 生物工程学报

By constructing the genomic DNA library of Meiothermus ruber CBS-01, the genes of trehalose phosphate synthase (TPS) and trehalose phosphate phosphatase (TPP) involved in trehalose synthesis were cloned. The genes were cloned into the plasmid pET21a, and expressed in Escherichia coli Rosetta gami (DE3). The activities of these two purified enzymes were confirmed by thin layer chromatography (TLC). Meanwhile, we tested the cellular compatible solutes of M. ruber CBS-01 under different environmental pressure, and found that under hyperosmotic pressure, this strain can accumulate trhalose-6-phosphate, but not trehalose. These results can give more insight to future research in the roles of TPS/TPP and TreS pathway.

Cloning and expression in Saccharomyces cerevisiae of delta5-fatty acid desaturase gene from Phaeodactylum tricornutum / 生物工程学报

Delta5-fatty acid desaturase is the key enzyme in synthesis of arachidonic acid. Two specific fragment was cloned from genomic DNA and total cDNA of Phaeodactylum tricornutum through PCR with primer designed according to the reported sequences, respectively 1520 bp and 1410 bp. Comparison of the genomic and cDNA sequences revealed that the delta5-fatty Acid Desaturase gene from genomic DNA had an 110 bp intron. The 1.4 kb was subcloned into the yeast-E. coli shuttle vector pYES2.0, then an expression recombinant plasmid pYPTD5 containerizing target gene was constructed. The plasmid pYPTD5 was transformed into defective mutant INCSc 1 of Saccharomyces cerevisiae for expression by electrotransformation method. Dihomo-gamma-linolenic acid was provided as an exogenous substrate to the yeast cultures, with galactose as inducer. By GC detecting, the recombinant S. cerecisiae had arachidonic acid. The results indicated that high level expression of delta5-fatty acid desaturase, and the substrate conversion reached 45.9%.

Regulating promoter element of iron-dependent gene FRP1 in Candida albicans by site-directed mutation / 生物工程学报

Microarray analysis revealed that the expression of ferric reductase (FRP1) can be regulated by the Riml01 protein. In order to find new transcriptional regulatory element in the promoter of FRP1, we analyzed the 1000 bp sequence upstream of ATG to find 2 potential Riml01p binding sites. We generated site-specific mutations in each of the two sites and fused these mutated promoters to LacZ. Then the promoter-LacZ fusion construct was recombinant into wild type and riml01-/- strains for beta-galactosidase assay. The results revealed that the FRP1 was up-regulated in alkaline pH and this was caused by iron starvation. The -650 site, not the -160 site, had an important role in FRP1 Riml01p-dependent expression. We conclude that Riml01p may interact with the -650 binding site of the promoter to regulate the FRP1 expression.

BREEDING OF A HIGH-?-LINOLENIC ACID YIELD PRODUCING STRAIN AND THE EXTRACTION OF FERMENTATION PRODUCT / 微生物学通报

Mortieralla isbellina (AS 3.3410) was used as the starting strain in the experiment. Through fermentation, the production rate of fungal body was 10%, content of lipid in fungal body was 27%, content of ?-Linolenic acid in lipid was 3.3%, When it was treated by U.V, mutant M_6 was obtained, its production rate of fungai body was 25%, lipid content was 32.8%, ?-linolenic acid content was 8.44%. Pass-generation test indicated that the heredity character of M_6 was stable.The optimum culture medium was obtained through culture condition test, and the result of fermentation in 10L tank showed that the production rate of fungal body was 29.3%, lipid content was 44.7%, GLA content was 9.44%.In the meantime, the method of extraction of fungai lipid was primarily studied, which indicated. that it is preferable to use a combination of ethanol and hexane to extract alternately.