Wine yeast selection in the Iberian Peninsula: Saccharomyces and non-Saccharomyces as drivers of innovation in Spanish and Portuguese wine industries

Yeast selection for the wine industry in Spain started in 1950 for the understanding of the microbial ecology, and for the selection of optimal strains to improve the performance of alcoholic fermentation and the overall wine quality. This process has been strongly developed over the last 30 years, firstly on Saccharomyces cerevisiae, and, lately, with intense activity on non-Saccharomyces. Several thousand yeast strains have been isolated, identified and tested to select those with better performance and/or specific technological properties. The present review proposes a global survey of this massive ex-situ preservation of eukaryotic microorganisms, a reservoir of biotechnological solutions for the wine sector, overviewing relevant screenings that led to the selection of strains from 12 genera and 22 species of oenological significance. In the first part, the attention goes to the selection programmes related to relevant wine-producing areas (i.e. Douro, Extremadura, Galicia, La Mancha and Uclés, Ribera del Duero, Rioja, Sherry area, and Valencia). In the second part, the focus shifted on specific non-Saccharomyces genera/species selected from different Spanish and Portuguese regions, exploited to enhance particular attributes of the wines. A fil rouge of the dissertation is the design of tailored biotechnological solutions for wines typical of given geographic areas.

Use of Torulaspora delbrueckii and Saccharomyces cerevisiae in semi-industrial sequential inoculation to improve quality of Palomino and Chardonnay wines in warm climates

AIMS

We have evaluated for the first time the impact of two commercial yeast strains (Torulaspora delbrueckii TD291 and Saccharomyces cerevisiae QA23) inoculated sequentially in musts of Chardonnay and Palomino Fino grape varieties grown under warm climate (South-west of Spain).

METHODS AND RESULTS

Semi-industrial scale alcoholic fermentations (AF) were performed during the 2011 and 2012 harvests. Implantation analyses demonstrated that T. delbrueckii is the predominant strain until the end of the AF phase. Wines with sequential inoculation (SI) resulted in the production of low levels of acetic acid (which gives wine an undesirable 'vinegary' character), low acetaldehyde in Chardonnay and high in Palomino wines. The most salient attributes that contribute to the quality of the Chardonnay and Palomino wines produced were aroma intensity, fresh and tropical fruit character.

CONCLUSIONS

This study demonstrated that SI of T. delbrueckii and S. cerevisiae contribute significantly to the improvement of Chardonnay wine aromas and the creation of new styles of wine for Palomino.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study has generated new knowledge about the biotechnological potential of T. delbrueckii (TD219) and S. cerevisiae (QA23) for improving the organoleptic properties of Chardonnay and Palomino wines.

Characterization of the gdhA gene from the phytopathogen Botrytis cinerea

A 3.48-kb DNA region containing the gdhA gene, which codifies the NADP-dependent glutamate dehydrogenase enzyme from Botrytis cinerea, has been cloned and characterized. A fragment of 2351 nucleotides was sequenced and found to contain an ORF of 1350 bp that encodes a protein of 450 amino acids. The gene, containing two introns that showed polymorphic size between them, was located by pulsed-field gel electrophoresis in chromosome X in seven strains, which were isolated from several hosts and had different levels of pathogenesis. The protein was similar to the gdhA of various other organisms, with nine highly conserved motifs that included the known active site sequence. The cloned gene was proven to be functional since it complemented two different Aspergillus nidulans gdhA mutants, restoring high levels of NADP-dependent glutamate dehydrogenase activity to the transformants. gdhA was transcribed as a monocistronic transcript of 1.7 kb starting at an A or a T, located 40 or 47 bp, respectively, upstream from the initial ATG codon of the ORF. Transcription levels of the gdhA gene were high during the rapid growth phase. Very high expression levels of the gdhA gene were observed in media with asparagine as the nitrogen source, whereas glutamic acid repressed transcription of the gdhA gene. Similarly high levels of gdhA gene transcription were observed in media with acetate as the carbon source, while glycerol strongly repressed gdhA gene transcription. These results indicate that expression of the gdhA gene is subject to strong nitrogen and carbon regulation at the transcriptional level.

[Genetic analysis and relationship to pathogenicity in Botrytis cinerea]

Botrytis cinerea is a plant-pathogenic fungus that produces the disease known as grey mould in a wide variety of agriculturally important hosts in many countries. Ten strains from different locations collected on different years have been isolated and characterized by several methods (morphological, biochemical, genetical and molecular). Results showed that clear morphological differences exist between strains, and showing a relationship between the presence of sclerotia and pathogenicity. The conidial size and the nuclear number were highly variable between different strains. Pulsed-field gel electrophoresis showed a unique karyotype for each strain, highly polymorphic between strains and with a number of bands ranging from 4 to 8. An efficient transformation system has been achieved through the plasmid pAMPF21, containing the region AMA1 of Aspergillus nidulans. Lastly, from a genomic library the gdhA gene has been cloned. This gene produces an RNAm of 1.7 Kb and complements the deficiency on glutamate dehydrogenase activity of A. nidulans.

An autonomously replicating plasmid transforms Botrytis cinerea to phleomycin resistance

A transformation system has been developed for the pathogen fungus Botrytis cinerea, based on the utilization of the wide host plasmid pUT737 that contains the Sh ble gene, conferring resistance to phleomycin. Transformed protoplasts were regenerated at 10-25 micrograms ml(-1) of phleomycin, at a frequency of 25-40 transformants per microgram of DNA, and they were resistant up to 50 micrograms ml(-1). Southern hybridization using undigested and digested total DNA showed the presence of circular autonomously replicating plasmid pUT737 in the transformants. Reisolated plasmid from transformed fungus transformed E. coli and rescued plasmid was identified as PUT737. Transformants were grown for four generations under non-selective conditions and replicative plasmids were still detected. Plasmids present in all transformants at this stage had been modified from native pUT737 and showed the same size and configuration indicating that selection through stabilizing plasmid forms has happened.

Delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine synthetase, the multienzyme integrating the four primary reactions in beta-lactam biosynthesis, as a model peptide synthetase

ACV synthetase forms the tripeptide precursor of penicillins and cephalosporins from alpha-aminoadipate, cysteine, and valine. Catalytic sites for substrate carboxyl activation as adenylates, peptide bond formations, epimerization and release of the tripeptide-thioester are integrated in multifunctional enzymes of 405 to 425 kD. These have been characterized from several pro- and eukaryotic beta-lactam producers. Implications of these results for the thio-template mechanism of peptide formation are discussed, as well as the use of this multienzyme as a model system for enzymatic peptide synthesis.

Biochemical characterization and molecular genetics of nine mutants of Penicillium chrysogenum impaired in penicillin biosynthesis

Nine mutants of Penicillium chrysogenum (npe1 to npe8 and npe10) impaired in penicillin biosynthesis were screened after nitrosoguanidine mutation. Mutants npe1, npe4, npe5, npe6, npe7, npe8, and npe10 failed to synthesize significant levels of penicillin, whereas strains npe2 and npe3 synthesized about 20% of the penicillin level produced by the parental strain. Mutants npe5 and npe10 did not show alpha-aminoadipylcysteinyl-valine (ACV) synthetase activity in vitro and did not form ACV in vivo. Immunoblotting analysis of the different mutants using antibodies raised against Aspergillus nidulans ACV-synthetase showed that mutants npe5 and npe10 lacked this multienzyme protein, which in the parental strain had a molecular mass of about 420 kDa, and mutants npe2 and npe3 formed reduced level of this protein. All mutants showed normal levels of isopenicillin N synthase, as shown by Western blot analysis and enzyme assays (except npe10 that lacked this enzyme and npe2 and npe3 that formed reduced levels); npe1, npe4, npe6, npe7, npe8, and npe10 lacked isopenicillin N acyltransferase. Southern hybridizations of total DNA of the parental strain and mutants npe5, npe6, npe8, and npe10 with probes internal to the pcbAB, pcbC, and penDE genes showed that mutants npe5, npe6, and npe8 had the same arrangement of the penicillin gene cluster carrying probably point mutations, but mutant npe10 lacked the three penicillin biosynthetic genes, suggesting that it had suffered a deletion of the entire penicillin cluster. Southern hybridization with a pyrG probe as control and fingerprinting analysis of total DNA of npe10 as compared to several P.chrysogenum strains and other Penicillium and Aspergillus species, confirmed that npe10 is a deletion mutant of P. chrysogenum that had lost the penicillin biosynthetic genes.

Cloning and characterization of the acyl-coenzyme A: 6-aminopenicillanic-acid-acyltransferase gene of Penicillium chrysogenum

A gene, aat, encoding acyl-CoA: 6-aminopenicillanic acid acyltransferase (AAT), the last enzyme of the penicillin (Pn) biosynthetic pathway, has been cloned from the genome of Penicillium chrysogenum AS-P-78. The gene contains three introns in the 5'-region and encodes a protein of 357 amino acids with an Mr of 39,943. It complements mutants of P. chrysogenum deficient in AAT activity. The aat gene is expressed as a 1.15-kb transcript and the encoded protein appears to be processed post-translationally into two nonidentical polypeptides of 102 and 255 aa, with Mrs of 11,498 and 28,461, respectively. Three proteins of 40, 11, and 29 kDa (the last one corresponding to the previously purified AAT), were identified in extracts of P. chrysogenum. The aa sequence of the N-terminal end of the 11-kDa polypeptide matched the nucleotide (nt) sequence of the 5'-region of aat. The N-terminal end of the 29-kDa polypeptide corresponded to the sequence beginning at nt position 916 of the sequenced DNA fragment (nt 441 of aat gene). The aat gene of P. chrysogenum resembles the genes encoding Pn acylases of Escherichia coli, Proteus rettgeri and Pseudomonas sp., all of which encode two nonidentical subunits derived from a common precursor, encoded by a single open reading frame.

Two genes involved in penicillin biosynthesis are linked in a 5.1 kb SalI fragment in the genome of Penicillium chrysogenum

Two genes, pcbC and penDE (also named ips and aat, respectively) encoding the enzymes isopenicillin N synthase and acyl-CoA:6-amino penicillanic acid (6-APA) acyltransferase, which are involved in the penicillin biosynthetic pathway in Penicillium chrysogenum, were cloned. Both genes are clustered together in a 5.1 kb SalI DNA fragment and are separated by a nontranscribed intergenic region of 1.5 kb. These genes are transcribed from different promoters in two separate transcripts of about 1.15 kb each. The penDE gene complements mutants of P. chrysogenum deficient in acyltransferase and the pcbC gene increases the level of isopenicillin N synthase in strains containing low levels of this enzyme. The clustering of penicillin biosynthetic genes is of great interest in the light of previous claims of horizontal transfer of the pcbC gene from beta-lactam producing Streptomyces to filamentous fungi.

Cloning, sequence analysis and transcriptional study of the isopenicillin N synthase of Penicillium chrysogenum AS-P-78

A gene (ips) encoding the isopenicillin N synthase of Penicillium chrysogenum AS-P-78 was cloned in a 3.9 kb SalI fragment using a probe corresponding to the amino-terminal end of the enzyme. The SalI fragment was trimmed down to a 1.3 kb NcoI-BglII fragment that contained an open reading frame of 996 nucleotides encoding a polypeptide of 331 amino acids with an Mr of 38012 dalton. The predicted polypeptide encoded by the ips gene of strain AS-P-78 contains a tyrosine at position 195, whereas the gene of the high penicillin producing strain 23X-80-269-37-2 shows an isoleucine at the same position. The ips gene is expressed in Escherichia coli minicells using the lambda phage PL promoter. Some similar sequence motifs were found in the upstream region of the ips gene of P. chrysogenum when compared with the upstream sequences of the ips genes of Cephalosporium acremonium and Aspergillus nidulans. Primer extension studies indicated that the start of the mRNA coincides with a T in position -11 which is located in a conserved pyrimidine-rich sequence, near two CAAG boxes. Clones of P. chrysogenum Wis 54-1255 transformed with the ips gene showed a five-fold higher isopenicillin N synthase activity than the untransformed cultures.

Glucokinase-deficient mutant of Penicillium chrysogenum is derepressed in glucose catabolite regulation of both beta-galactosidase and penicillin biosynthesis

One glucokinase-deficient mutant (glk1) of Penicillium chrysogenum AS-P-78 was isolated after germ tube-emitting spores were mutated with nitrosoguanidine and selected for growth on lactose-containing medium in the presence of inhibitory concentrations of D-2-deoxyglucose (3 mM). Penicillin biosynthesis was greatly reduced (55%) in D-glucose-grown cultures of the parental strain, but this sugar had no repressive effect on the rate of penicillin biosynthesis in the mutant glk1. This mutant was deficient in ATP-dependent glucokinase and showed a greatly reduced uptake of D-glucose. The parental strain P. chrysogenum AS-P-78 showed in vitro ATP-dependent phosphorylating activities of D-glucose, D-2-deoxyglucose, and D-galactose. The glk1 mutant was deficient in the in vitro phosphorylation of D-glucose and D-2-deoxyglucose but retained a normal D-galactose-phosphorylating activity. D-Glucose repressed both beta-galactosidase and isopenicillin-N-synthase but not acyl coenzyme A:6-aminopenicillanic acid acyltransferase in the parental strain. The glucokinase-deficient mutant was simultaneously derepressed in carbon catabolite regulation of beta-galactosidase and isopenicillin-N-synthase, suggesting that a common regulatory mechanism is involved in carbon catabolite regulation of both sugar utilization and penicillin biosynthesis.

Purification to homogeneity and characterization of acyl coenzyme A:6-aminopenicillanic acid acyltransferase of Penicillium chrysogenum

The acyl coenzyme A (CoA):6-aminopenicillanic acid (6-APA) acyltransferase of Penicillium chrysogenum AS-P-78 was purified to homogeneity, as concluded by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and isoelectric focusing. The enzyme is a monomer with a molecular weight of 30,000 +/- 1,000 and a pI of about 5.5. The optimal pH and temperature were 8.0 and 25 degrees C, respectively. This enzyme converts 6-APA into penicillin by using phenylacetyl CoA or phenoxyacetyl CoA as acyl donors. The pure enzyme showed a high specificity and affinity for 6-APA and did not accept benzylpenicillin, 7-aminocephalosporanic acid, cephalosporin C, or isocephalosporin C as substrates. The enzyme converted isopenicillin N into penicillin G, although with a lower efficiency than when 6-APA was used as the substrate. It did not show penicillin G acylase activity. The acyl CoA:6-APA acyltransferase required dithiothreitol or other thiol-containing compounds, and it was protected by thiol-containing reagents against thermal inactivation. The acyltransferase was inhibited by several divalent and trivalent cations and by p-chloromercuribenzoate and N-ethylmaleimide. The activity was absent in four different mutants that were blocked in penicillin biosynthesis.