Engineering pathways for malate degradation in Saccharomyces cerevisiae.

Deacidification of grape musts is crucial for the production of well-balanced wines, especially in colder regions of the world. The major acids in wine are tartaric and malic acid. Saccharomyces cerevisiae cannot degrade malic acid efficiently due to the lack of a malate transporter and the low substrate affinity of its malic enzyme. We have introduced efficient pathways for malate degradation in S. cerevisiae by cloning and expressing the Schizosaccharomyces pombe malate permease (mae1) gene with either the S. pombe malic enzyme (mae2) or Lactococcus lactis malolactic (mleS) gene in this yeast. Under aerobic conditions, the recombinant strain expressing the mae1 and mae2 genes efficiently degraded 8 g/L of malate in a glycerol-ethanol medium within 7 days. The recombinant malolactic strain of S. cerevisiae (mae1 and mleS genes) fermented 4.5 g/L of malate in a synthetic grape must within 4 days.

Emergence of zidovudine and multidrug-resistance mutations in the HIV-1 reverse transcriptase gene in therapy-naive patients receiving stavudine plus didanosine combination therapy. STADI Group.

OBJECTIVE: Assessment of genotypic changes in the reverse transcriptase gene of HIV-1 occurring in antiretroviral naive patients treated by stavudine plus didanosine combination therapy. METHODS: Sequence analysis (codons 1-230) was performed after amplification of the reverse transcriptase gene from plasma samples collected at baseline and at the end of treatment from 39 previously treatment-naive patients treated for 24-48 weeks. RESULTS: At baseline, mutations associated with zidovudine resistance were detected in plasma from two patients: Asp67Asn/Lys219Gln and Leu210Trp. Among the 39 subjects, 18 (46%) developed mutations: one developed the Val75Thr/Ala mutation, four (10%) developed a Gln151Met multidrug-resistance mutation (MDR), associated in one of them with the Phe77Leu and the Phe116Tyr MDR mutations and 14 (36%) developed one or more zidovudine-specific mutations (Met41Leu, Asp67Asn, Lys70Arg, Leu210Trp, Thr215Tyr/Phe). The development of a Met41Leu zidovudine-specific mutation was associated with the development of a Gln151Met mutation in one patient. Other reverse transcriptase mutations known to confer resistance to nucleoside analogues were not detected. At inclusion, there was no statistical difference in HIV-1 load between patients who developed resistance mutations and those who did not. RNA HIV-1 load decrease was higher (P = 0.05) in patients who maintained a wild-type reverse transcriptase genotype (-2.22 log10 copies/ml) than in patients who developed resistance mutations (-1.14 log10 copies/ml). CONCLUSION: Stavudine/didanosine combination therapy is associated with emergence of zidovudine-related resistance or MDR mutations in naive patients. These findings should be considered when optimizing salvage therapy for patients who have received a treatment including stavudine/didanosine combination.

Zidovudine resensitization and dual HIV-1 resistance to zidovudine and lamivudine in the delta lamivudine roll-over study.

OBJECTIVE: To study zidovudine resensitization and dual resistance to zidovudine/lamivudine in HIV-1 isolates from nucleoside reverse transcriptase (RT) inhibitor-experienced patients during selective pressure exerted by zidovudine/lamivudine combination therapy. DESIGN AND METHODS: HIV-1 isolates from 29 patients receiving zidovudine/lamivudine combination therapy in the Delta roll-over study were analysed at entry and during a 1 year follow-up period for phenotypic susceptibility to zidovudine and lamivudine in the ANRS PBMC assay. The RT gene from codon 20 to 230 and at codon 333 was analysed by nucleotide sequencing of the corresponding isolates. RESULTS: HIV-1 isolates from 23 of the 29 patients were phenotypically resistant to zidovudine at baseline; 61% of these patients showed significant zidovudine resensitization during follow-up. The zidovudine IC50 value correlated positively with log10 plasma HIV-1 RNA (P = 0.02) and negatively with the CD4 cell count (P = 0.004). Zidovudine resensitization (related to acquisition of the M184V mutation) was transient, with evolution towards dual resistance to zidovudine and lamivudine in 20 of the 29 patients. The phenotype of certain dually resistant isolates coincided with the emergence of multiple mutations in the 5' part of the RT gene. CONCLUSIONS: M184V-mediated zidovudine resensitization of HIV-1 is transient in most patients who are given zidovudine/lamivudine combination therapy when zidovudine resistance has already emerged. The subsequent evolution towards dual phenotypic resistance to zidovudine/lamivudine corresponds to complex genotypic profiles.

Functional expression in Saccharomyces cerevisiae of the Lactococcus lactis mleS gene encoding the malolactic enzyme.

Malolactic fermentation, a crucial step in winemaking, results mostly in degradation by lactic acid bacteria of L-malic acid into L-lactic acid. This direct decarboxylation is catalysed by the malolactic enzyme. Recently we, and others, have cloned the mleS gene of Lactococcus lactis encoding malolactic enzyme. Heterologous expression of mleS in Saccharomyces cerevisiae was tested to perform simultaneously alcoholic and malolactic fermentations by yeast. mleS gene was cloned in a yeast multicopy vector under a strong promoter. Malolactic activity was present in crude extracts of recombinant yeasts. Malic acid degradation was tested during alcoholic fermentation in synthetic media and must. Yeasts expressing the mleS gene actually produced L-lactate from L-malate; nevertheless malate degradation was far from complete.

Cloning and sequence analysis of the gene encoding Lactococcus lactis malolactic enzyme: relationships with malic enzymes.

Malolactic enzyme is the key enzyme in the degradation of L-malic acid by lactic acid bacteria. Using degenerated primers designed from the first 20 N-terminal amino acid sequence of lactococcal malolactic enzyme, a 60-bp DNA fragment containing part of the mleS gene was amplified from Lactococcus lactis in a polymerase chain reaction. This specific probe was used to isolate two contiguous fragments covering the gene as a whole. The 1.9-kb region sequenced contains an open reading frame of 1623 bp, coding a putative protein of 540 amino acids. The deduced amino acid sequence reveals that lactococcal putative protein (Mlep) is highly homologous to the malic enzyme of other organisms. Expression of the mleS gene in Escherichia coli results in malolactic activity.

Identification of surface proteins involved in the adhesion of a probiotic Bacillus cereus strain to mucin and fibronectin.

Several Bacillus strains isolated from commercial probiotic preparations were identified at the species level, and their adhesion capabilities to three different model intestinal surfaces (mucin, Matrigel and Caco-2 cells) were assessed. In general, adhesion of spores was higher than that of vegetative cells to the three matrices, and overall strain Bacillus cereus(CH) displayed the best adhesion. Different biochemical treatments revealed that surface proteins of B. cereus(CH) were involved in the adhesion properties of the strain. Surface-associated proteins from vegetative cells and spores of B. cereus(CH) were extracted and identified, and some proteins such as S-layer components, flagellin and cell-bound proteases were found to bind to mucin or fibronectin. These facts suggest that those proteins might play important roles in the interaction of this probiotic Bacillus strain within the human gastrointestinal tract.

Two allelic genes responsible for vegetative incompatibility in the fungus Podospora anserina are not essential for cell viability.

Vegetative incompatibility is a lethal reaction that destroys the heterokaryotic cells formed by the fusion of hyphae of non-isogenic strains in many fungi. That incompatibility is genetically determined is well known but the function of the genes triggering this rapid cell death is not. The two allelic incompatibility genes, s and S, of the fungus Podospora anserina were characterized. Both encode 30 kDa polypeptides, which differ by 14 amino acids between the two genes. These two proteins are responsible for the incompatibility reaction that results when cells containing s and S genes fuse. Inactivation of the s or S gene by disruption suppresses incompatibility but does not affect the growth or the sexual cycle of the mutant strains. This suggests that these incompatibility genes have no essential function in the life cycle of the fungus.

Incidence of SUC-RTM telomeric repeated genes in brewing and wild wine strains of Saccharomyces.

When over-expressed, RTM yeast genes confer resistance to the toxicity of molasses. They are found in distiller's and baker's industrial yeasts in multiple copies, scattered on the telomeres and physically linked to the telomeric SUC genes. Because these genes are absent from some laboratory strains, we explored the genomes of other industrial yeasts (brewing strains) and wine wild strains. A collection of 47 wine yeast strains (S. cerevisiae and S. bayanus) and 15 brewing strains, lager, ale and possible ancestors (S. monacensis, S. paradoxus and S. carlsbergensis) were screened for the presence of RTM genes. Only three wine strains and all brewing strains proved to contain RTM sequences in different copy numbers. PCR and chromosome blotting confirm the presence of SUC sequences in tandem with RTM. Moreover, analysis of the entire S. cerevisiae genome sequence shows that three other, non-telomeric, genes related to RTM are scattered on different chromosomes.