Role of Hypermutability in the Evolution of the Genus Oenococcus

Among the lactic acid bacteria (LAB) present in the oenological microbial ecosystem, Oenococcus oeni, an acidophilic lactic acid bacterium, is essential during winemaking. It outclasses all other bacterial species during malolactic fermentation (MLF). Oenological performances, such as malic acid degradation rate and sensorial impact, vary significantly according to the strain. The genetic diversity of the O. oeni species was evaluated using a multilocus sequence typing (MLST) scheme. Seven housekeeping genes were sequenced for a collection of 258 strains that had been isolated all over the world (particularly Burgundy, Champagne, and Aquitaine, France, Chile, South Africa, and Italy) and in several wine types (red wines, white wines, and champagne) and cider. The allelic diversity was high, with an average of 20.7 alleles per locus, many of them being rare alleles. The collection comprised 127 sequence types, suggesting an important genotypic diversity. The neighbor-joining phylogenetic tree constructed from the concatenated sequence of the seven housekeeping genes showed two major phylogenetic groups, named A and B. One unique strain isolated from cider composed a third group, rooting the phylogenetic tree. However, all other strains isolated from cider were in group B. Eight phylogenetic subgroups were statistically differentiated and could be delineated by the analysis of only 32 mutations instead of the 600 mutations observed in the concatenated sequence of the seven housekeeping genes. Interestingly, in group A, several phylogenetic subgroups were composed mostly of strains coming from a precise geographic origin. Three subgroups were identified, composed of strains from Chile, South Africa, and eastern France.

Section: Discussionmentioning

confidence: 64%

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confidence: 99%

Evidence of Distinct Populations and Specific Subpopulations within the SpeciesOenococcus oeni

Bridier

Claisse

Coton³

et al. 2010

“…This high level of sequence identity may be due to high requirements in amino acid conservation to ensure glycosyltransferase activity, or it may indicate recent horizontal transfer between species (5, 25, 27, 30, 33, 38). Actually, frequent horizontal transfers are thought to be the cause of the high level of diversity within the species O. oeni (11,39,53) and may promote the evolution of bacterial gene loci through genomic island interexchange (5,8,24,25,30,38,53). Genomic islands can display very different structures, modes of acquisition, or mobility mechanisms (8,24).…”

Section: Discussionmentioning

confidence: 99%

Characterization ofgtf, a Glucosyltransferase Gene in the Genomes ofPediococcus parvulusandOenococcus oeni, Two Bacterial Species Commonly Found in Wine

Dols‐Lafargue

Lee

Marrec

et al. 2008

"Ropiness" is a bacterial alteration in wines, beers, and ciders, caused by ␤-glucan-synthesizing pediococci. A single glucosyltransferase, Gtf, controls ropy polysaccharide synthesis. In this study, we show that the corresponding gtf gene is also present on the chromosomes of several strains of Oenococcus oeni isolated from nonropy wines. gtf is surrounded by mobile elements that may be implicated in its integration into the chromosome of O. oeni. gtf is expressed in all the gtf ؉ strains, and ␤-glucan is detected in the majority of these strains. Part of this ␤-glucan accumulates around the cells forming a capsule, while the other part is liberated into the medium together with heteropolysaccharides. Most of the time, this polymer excretion does not lead to ropiness in a model medium. In addition, we show that wild or recombinant bacterial strains harboring a functional gtf gene (gtf ؉ ) are more resistant to several stresses occurring in wine (alcohol, pH, and SO 2 ) and exhibit increased adhesion capacities compared to their gtf mutant variants."Ropiness" or "oiliness" is one of the major bacterial alterations in wine. It has no impact on human health. However, the viscosity of the spoiled wines prevents their commercialization (43,54,55). Many microbial species have been isolated from ropy wines: Streptococcus mucilaginous and Leuconostoc and Lactobacillus species (15,18,34,36,53,55). However, the species most often incriminated is Pediococcus parvulus (15,31,48,53). Different strains have been isolated from red and white ropy wines from the Bordeaux region in France or from Basque country ropy ciders and were then shown to cause ropiness when grown in model media. These strains were first called Pediococcus cerevisiae (31), later classified as Pediococcus damnosus by DNA/DNA hybridizations (15, 32), and then finally classified as Pediococcus parvulus based on 16S RNA sequencing (53). The increase in viscosity of wine or model media caused by P. parvulus is due to the production of a high-molecular-weight ␤-glucan. This fibrillar polymer consists of a trisaccharide repeating unit with a ␤-1,3-linked glucosyl backbone and branches made up of single ␤-1,2-linked D-glucopyranosyl residues (16,17,28). The level of production of soluble ␤-glucan by pediococci is low (200 mg/liter at most) and is only slightly modified by external growth parameters (49, 50). Polymer production is controlled by a single transmembrane glucosyltransferase, Gtf, a 567-amino-acid, 65-kDa protein that polymerizes glucosyl residues from UDP glucose (53). Gtf exhibits significant homology with Tts (32% identical amino acids), an inverting glucosyltransferase produced by Streptococcus pneumoniae type 37, which synthesizes a branched ␤-1,3 ␤-1,2 glucan whose structure is very close to that of the glucan causing ropiness (1, 29). Actually, the antibodies targeting the type 37 polysaccharide capsule also agglutinate ropy pediococci (51). The gtf gene encoding Gtf is highly conserved (99.9% identity) in wine-and cider-spoiling bacteria, as it...

“…O. oeni lacks the mutS and mutL mismatch repair genes, which has been suggested to contribute to its hypermutable status and its accelerated evolution. It is likely that this factor contributed to the unique adaptation of O. oeni to acidic and alcoholic environments that made it an ideal organism for the malolactic fermentation during the production of wine (7,29). However, elevated mutation rates may also result in deterioration of industrial fermentation properties (19,20,51).…”

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confidence: 99%

Indigenous and Environmental Modulation of Frequencies of Mutation in Lactobacillus plantarum

Machielsen

Alen-Boerrigter

Koole

et al. 2010

Reliability of microbial (starter) strains in terms of quality, functional properties, growth performance, and robustness is essential for industrial applications. In an industrial fermentation process, the bacterium should be able to successfully withstand various adverse conditions during processing, such as acid, osmotic, temperature, and oxidative stresses. Besides the evolved defense mechanisms, stress-induced mutations participate in adaptive evolution for survival under stress conditions. However, this may lead to accumulation of mutant strains, which may be accompanied by loss of desired functional properties. Defining the effects of specific fermentation or processing conditions on the mutation frequency is an important step toward preventing loss of genome integrity and maintaining the productivity of industrial strains. Therefore, a set of Lactobacillus plantarum mutator reporter strains suitable for qualitative and quantitative analysis of lowfrequency mutation events was developed. The mutation reporter system constructed was validated by using chemical mutagenesis (N-methyl-N-nitro-N-nitrosoguanidine) and by controlled expression of endogenous candidate mutator genes (e.g., a truncated derivative of the L. plantarum hexA gene). Growth at different temperatures, under low-pH conditions, at high salt concentrations, or under starvation conditions did not have a significant effect on the mutation frequency. However, incubation with sublethal levels of hydrogen peroxide resulted in a 100-fold increase in the mutation frequency compared to the background mutation frequency. Importantly, when cells of L. plantarum were adapted to 42°C prior to treatment with sublethal levels of hydrogen peroxide, there was a 10-fold increase in survival after peroxide treatment, and there was a concomitant 50-fold decrease in the mutation frequency. These results show that specific environmental conditions encountered by bacteria may significantly influence the genetic stability of strains, while protection against mutagenic conditions may be obtained by pretreatment of cultures with other, nonmutagenic stress conditions.