Species attribution and strain typing of Oenococcus oeni (formerly Leuconostoc oenos) with restriction endonuclease fingerprints

Distribution of Oenococcus oeni populations in natural habitats

Oenococcus oeni is the lactic acid bacteria species most commonly encountered in wine, where it develops after the alcoholic fermentation and achieves the malolactic fermentation that is needed to improve the quality of most wines. O. oeni is abundant in the oenological environment as well as in apple cider and kombucha, whereas it is a minor species in the natural environment. Numerous studies have shown that there is a great diversity of strains in each wine region and in each product or type of wine. Recently, genomic studies have shed new light on the species diversity, population structure, and environmental distribution. They revealed that O. oeni has unique genomic features that have contributed to its fast evolution and adaptation to the enological environment. They have also unveiled the phylogenetic diversity and genomic properties of strains that develop in different regions or different products. This review explores the distribution of O. oeni and the diversity of strains in natural habitats.

Implications of new research and technologies for malolactic fermentation in wine

The initial conversion of grape must to wine is an alcoholic fermentation (AF) largely carried out by one or more strains of yeast, typically Saccharomyces cerevisiae. After the AF, a secondary or malolactic fermentation (MLF) which is carried out by lactic acid bacteria (LAB) is often undertaken. The MLF involves the bioconversion of malic acid to lactic acid and carbon dioxide. The ability to metabolise L-malic acid is strain specific, and both individual Oenococcus oeni strains and other LAB strains vary in their ability to efficiently carry out MLF. Aside from impacts on acidity, LAB can also metabolise other precursors present in wine during fermentation and, therefore, alter the chemical composition of the wine resulting in an increased complexity of wine aroma and flavour. Recent research has focused on three main areas: enzymatic changes during MLF, safety of the final product and mechanisms of stress resistance. This review summarises the latest research and technological advances in the rapidly evolving study of MLF and investigates the directions that future research may take.

Development of a sequence-characterized amplified region marker-targeted quantitative PCR assay for strain-specific detection of Oenococcus oeni during wine malolactic fermentation

Control over malolactic fermentation (MLF) is a difficult goal in winemaking and needs rapid methods to monitor Oenococcus oeni malolactic starters (MLS) in a stressful environment such as wine. In this study, we describe a novel quantitative PCR (QPCR) assay enabling the detection of an O. oeni strain during MLF without culturing. O. oeni strain LB221 was used as a model to develop a strain-specific sequence-characterized amplified region (SCAR) marker derived from a discriminatory OPA20-based randomly amplified polymorphic DNA (RAPD) band. The 5' and 3' flanking regions and the copy number of the SCAR marker were characterized using inverse PCR and Southern blotting, respectively. Primer pairs targeting the SCAR sequence enabled strain-specific detection without cross amplification of other O. oeni strains or wine species of lactic acid bacteria (LAB), acetic acid bacteria (AAB), and yeasts. The SCAR-QPCR assay was linear over a range of cell concentrations (7 log units) and detected as few as 2.2 × 10(2) CFU per ml of red wine with good quantification effectiveness, as shown by the correlation of QPCR and plate counting results. Therefore, the cultivation-independent monitoring of a single O. oeni strain in wine based on a SCAR marker represents a rapid and effective strain-specific approach. This strategy can be adopted to develop easy and rapid detection techniques for monitoring the implantation of inoculated O. oeni MLS on the indigenous LAB population, reducing the risk of unsuccessful MLF.

Characterization and technological properties of Oenococcus oeni strains from wine spontaneous malolactic fermentations: a framework for selection of new starter cultures

AIMS

To characterize the genetic and phenotypic diversity of 135 lactic acid bacteria (LAB) strains isolated from Italian wines that undergone spontaneous malolactic fermentation (MLF) and propose a multiphasic selection of new Oenococcus oeni malolactic starters.

METHODS AND RESULTS

One hundred and thirty-five LAB strains were isolated from 12 different wines. On the basis of 16S amplified ribosomal DNA restriction analysis (ARDRA) with three restriction enzymes and 16S rRNA gene sequencing, 120 O. oeni strains were identified. M13-based RAPD analysis was employed to investigate the molecular diversity of O. oeni population. Technological properties of different O. oeni genotypes were evaluated in synthetic medium at increasing selective pressure, such as low pH (3.5, 3.2 and 3.0) and high ethanol values (10, 11 and 13% v/v). Finally, the malolactic activity of one selected strain was assessed in wine by malolactic trial in winery.

CONCLUSIONS

The research explores the genomic diversity of wine bacteria in Italian wines and characterizes their malolactic metabolism, providing an efficient strategy to select O. oeni strains with desirable malolactic performances and able to survive in conditions simulating the harsh wine environment.

SIGNIFICANCE AND IMPACT OF THE STUDY

This article contributes to a better understanding of microbial diversity of O. oeni population in Italian wines and reports a framework to select new potentially O. oeni starters from Italian wines during MLF.

Multilocus sequence typing of Oenococcus oeni: detection of two subpopulations shaped by intergenic recombination

Oenococcus oeni is the acidophilic lactic acid bacterial species most frequently associated with malolactic fermentation of wine. Since the description of the species (formerly Leuconostoc oenos), characterization of indigenous strains and industrially produced cultures by diverse typing methods has led to divergent conclusions concerning the genetic diversity of strains. In the present study, a multilocus sequence typing (MLST) scheme based on the analysis of eight housekeeping genes was developed and tested on a collection of 43 strains of diverse origins. The eight targeted loci were successfully amplified and sequenced for all isolates. Only three to 11 different alleles were detected for these genes. The average nucleotide diversity also was rather limited (0.0011 to 0.0370). Despite this limited allelic diversity, the combination of alleles of each strain disclosed 34 different sequence types, which denoted a significant genotypic diversity. A phylogenetic analysis of the concatenated sequences showed that all strains form two well distinct groups of 28 and 15 strains. Interestingly, the same groups were defined by pulsed-field gel electrophoresis, although this method targets different genetic variations. A minimum spanning tree analysis disclosed very few and small clonal complexes. In agreement, statistical analyses of MLST data suggest that recombination events were important during O. oeni evolution and contributed to the wide dissemination of alleles among strains. Taken together, our results showed that MLST is more efficient than pulsed-field gel electrophoresis for typing O. oeni strains, and they provided a picture of the O. oeni population that explains some conflicting results previously obtained.

Role of hypermutability in the evolution of the genus Oenococcus

Oenococcus oeni is an alcohol-tolerant, acidophilic lactic acid bacterium primarily responsible for malolactic fermentation in wine. A recent comparative genomic analysis of O. oeni PSU-1 with other sequenced lactic acid bacteria indicates that PSU-1 lacks the mismatch repair (MMR) genes mutS and mutL. Consistent with the lack of MMR, mutation rates for O. oeni PSU-1 and a second oenococcal species, O. kitaharae, were higher than those observed for neighboring taxa, Pediococcus pentosaceus and Leuconostoc mesenteroides. Sequence analysis of the rpoB mutations in rifampin-resistant strains from both oenococcal species revealed a high percentage of transition mutations, a result indicative of the lack of MMR. An analysis of common alleles in the two sequenced O. oeni strains, PSU-1 and BAA-1163, also revealed a significantly higher level of transition substitutions than were observed in other Lactobacillales species. These results suggest that the genus Oenococcus is hypermutable due to the loss of mutS and mutL, which occurred with the divergence away from the neighboring Leuconostoc branch. The hypermutable status of the genus Oenococcus explains the observed high level of allelic polymorphism among known O. oeni isolates and likely contributed to the unique adaptation of this genus to acidic and alcoholic environments.

Intraspecific diversity of Oenococcus oeni strains determined by sequence analysis of target genes

Using molecular techniques and sequencing, we studied the intraspecific diversity of Oenococcus oeni, a lactic acid bacterium involved in red winemaking. A relationship between the phenotypic and genotypic characterization of 16 O. oeni strains isolated from wine with different levels of enological potential was shown. The study was based on the comparative genomic analysis by subtractive hybridization between two strains of O. oeni with opposite enological potential. The genomic sequences obtained from subtractive hybridization were amplified by polymerase chain reaction and sequenced for the 16 strains. A considerable diversity among strains of O. oeni was observed.

Evaluation of intra-specific diversities in Oenococcus oeni through analysis of genomic and expressed DNA

In winemaking Oenococcus (O.) oeni is the most frequent species of lactic acid bacteria (LAB) associated with malolactic fermentation (MLF). Several studies have demonstrated that O. oeni is a quite homogeneous species and strains are difficult to differentiate especially when isolates from the same region are analyzed. In this study, the molecular biodiversity of O. oeni isolated from wines of the same region (Aglianico produced in Basilicata Region, Southern Italy) was evaluated with the aim of designing a molecular approach for discrimination and characterization of the isolates at the strain level. Three molecular techniques were applied: random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR), restriction endonucleases analysis-pulsed field gel electrophoresis (REA-PFGE) and differential display PCR (DD-PCR). The results obtained by RAPD-PCR confirmed the difficulty in differentiating isolates. By means of REA-PFGE a higher polymorphism, often related to the origin (winery) of strains, was revealed. However, on analyzing strains isolated from the same winery, only in some cases was more than one REA-PFGE pattern obtained. By analyzing dendrograms constructed on the basis of DD-PCR profiles differentiation of strains isolated from the same winery, in some cases, could be accomplished. The reliability of the DD-PCR in the differentiation of closely related strains suggests that this method could represent an alternative and/or additional tool to other molecular methods, such as REA-PFGE, for fine characterization of oenococcal strains.

Allelic diversity and population structure in Oenococcus oeni as determined from sequence analysis of housekeeping genes

Oenococcus oeni is the organism of choice for promoting malolactic fermentation in wine. The population biology of O. oeni is poorly understood and remains unclear. For a better understanding of the mode of genetic variation within this species, we investigated by using multilocus sequence typing (MLST) with the gyrB, pgm, ddl, recP, and mleA genes the genetic diversity and genetic relationships among 18 O. oeni strains isolated in various years from wines of the United States, France, Germany, Spain, and Italy. These strains have also been characterized by ribotyping and restriction fragment length polymorphism (RFLP) analysis of the PCR-amplified 16S-23S rRNA gene intergenic spacer region (ISR). Ribotyping grouped the strains into two groups; however, the RFLP analysis of the ISRs showed no differences in the strains analyzed. In contrast, MLST in oenococci had a good discriminatory ability, and we have found a higher genetic diversity than indicated by ribotyping analysis. All sequence types were represented by a single strain, and all the strains could be distinguished from each other because they had unique combinations of alleles. Strains assumed to be identical showed the same sequence type. Phylogenetic analyses indicated a panmictic population structure in O. oeni. Sequences were analyzed for evidence of recombination by split decomposition analysis and analysis of clustered polymorphisms. All results indicated that recombination plays a major role in creating the genetic heterogeneity of O. oeni. A low standardized index of association value indicated that the O. oeni genes analyzed are close to linkage equilibrium. This study constitutes the first step in the development of an MLST method for O. oeni and the first example of the application of MLST to a nonpathogenic food production bacteria.

Phenotypic and genotypic characterization of Oenococcus oeni strains isolated from Italian wines

A phenotypic and genotypic characterization of 84 Oenococcus oeni isolates from Italian wines of different oenological areas was carried out. Numerical analysis of fatty acid profiles grouped the isolates into two clusters at low level of similarity (63%), the minor cluster containing seven isolates besides the type and the reference strains. Forthy-eight O. oeni isolates, representative of the two clusters, showed no differences in their metabolic properties (heterolactic fermentation pattern, citrate degradation capability and formation of some secondary metabolites). Moreover, the analysis of species-specific randomly amplified polymorphic DNA and 16S-23S rDNA intergenic spacer region polymorphism as well as the sequence-specific separation of V3 region from 16S rDNA by denaturing gradient gel electrophoresis demonstrated a substantial homogeneity among the isolates. On the basis of ApaI Pulsed Field Gel Electrophoresis (PFGE) restriction patterns, the 84 isolates were grouped into five different clusters at 70% similarity, but no correlation with the phenotypic groups could be demonstrated. However, by combining phenotypic and genotypic data, the 84 O. oeni isolates grouped into eight phenotypic-genotypic combined profiles and a relationship between the origin of the isolates and their combined profile became evident, so that a sort of strain specificity can be envisaged for each wine-producing area.

Physical map of the genome of Oenococcus oeni PSU-1 and localization of genetic markers

A physical map of the chromosome of Oenococcus oeni PSU-1 was constructed. This represents the first map for a strain of this species. A total of 37 restriction sites for the rare-cutting endonucleases Ascl, Fsel, Notl and Sfil were mapped on the chromosome, which was found to be circular with an estimated size of 1857 kb. Fragment order was determined using several approaches: analysis of partial and double digestions, two-dimensional pulsed-field gel electrophoresis, isolation of linking clones, and Southern hybridization with labelled restriction fragments both from PSU-1 and from O. oeni strain GM. Oenococcal genes alsS/alsD, mleA and mir, two phage attachment sites and recurrent sequences such as IS1165-like elements and rrn loci were located on the physical map. Specific fragments hybridizing with gene probes from Lactococcus lactis, Leuconostoc mesenteroides and Bacillus subtilis were also identified. The two ribosomal operons have been precisely located and their transcription direction determined.

Genotypic diversity and typing of cyanobacterial strains of the genus Arthrospira by very sensitive total DNA restriction profile analysis

Arthrospira maxima and A. platensis are two species of cyanobacteria cultivated and sold as health food, animal feed and source of food additives and fine chemicals. The genotypic diversity of several strains attributed to these two species on the basis of morphological criteria was investigated using very sensitive total DNA restriction profile analysis. The restriction profiles were obtained after sodium dodecyl sulphate polyacrylamide gel electrophoresis and silver staining. The unweighted pair-group method using arithmetic averages applied to the matrix of Dice similarity coefficient values clustered the electropherograms of the strains in two well-separated genotypic groups. These clusters corresponded to those obtained with morphological criteria. The molecular approach used was also able to type the examined strains.