Photo: Jeff Broadbent, Utah State University

On the basis of 16S rRNA sequence, Dicks et al. (2) proposed a reclassification of Leuconostoc oenos into a new genus, Oenococcus oeni. O. oeni shares relatively little DNA homology with the other genera in the Leuconostoc branch of the LAB (1). Woese argued that O. oeni is an example of a fast-evolving microorganism (7). Subsequent comparisons of RNA polymerase genes contradicted this view (5). Whole genomic comparisons between O. oeni and the nonacidophilic Leuconostoc mesenteroides (also sequenced as part of the LABGC project) will help resolve this issue and shed light on the evolution of this unusual branch.

Perhaps the most studied aspect of O. oeni is the ability to convert malate to lactate (the malolactic conversion). This involves uptake of malate, its decarboxylation to L-lactic acid and CO2, and subsequent export of end products. The malolactic conversion generates energy for the cell in the form of a proton motive force (6). Recently the genes encoding the malate decarboxylase and malate permease have been cloned and characterized (3, 4).

Most likely due to difficulties in gene transfer, there are few studies employing genetic strategies to examine O. oeni. Several bacteriophages and plasmids have been characterized (6). In addition, the broad host range transposon Tn916 has been mobilized into the O. oeni genome (8). To date, however, few chromosomal genes from O. oeni have been sequenced (< 20 entries in GenBank).

Many researchers have examined the diversity of O. oeni strains within and around wineries. Studies have employed various molecular typing methods (protein profiling, plasmid profiling, RAPD, PFGE, rDNA RFLP, etc.) to discern regional differences in strains. An outcome of this analysis is the general view that Oenococcus is a genetically homogenous genus.

The strain sequenced in this project, O. oeni PSU-1, was originally isolated at Penn State University and is currently employed commercially to carry out the malolactic fermentation wines.

References:

1. Dellaglio, F., L. M. T. Dicks, and S. Torriani. 1995. The genus Leuconostoc, p. 235-278. In B. J. B. W. a. W. H. Holzapfel (ed.), The Genera of Lactic Acid Bacteria, vol. 2. Blackie Academic & Professional, London.
2. Dicks, L. M., F. Dellaglio, and M. D. Collins. 1995. Proposal to reclassify Leuconostoc oenos as Oenococcus oeni [corrig.] gen. nov., comb. nov. International Journal of Systematic Bacteriology 45:395-7.
3. Labarre, C., C. Diviès, and J. Guzzo. 1996. Genetic organization of the mle locus and identification of a mleR-like gene from Leuconostoc oenos. Applied and Environmental Microbiology 62:4493-8.
4. Labarre, C., J. Guzzo, J. F. Cavin, and C. Diviès. 1996. Cloning and characterization of the genes encoding the malolactic enzyme and the malate permease of Leuconostoc oenos. Applied and Environmental Microbiology 62:1274-82.
5. Morse, R., M. D. Collins, K. Ohanlon, S. Wallbanks, and P. T. Richardson. 1996. Analysis of the beta' subunit of DNA-dependent RNA polymerase does not support the hypothesis inferred from 16S rRNA analysis that Oenococcus oeni (formerly Leuconostoc oenos) is a tachytelic (fast-evolving) bacterium. International Journal of Systematic Bacteriology 46:1004-1009.
6. Versari, A., G. P. Parpinello, and M. Cattaneo. 1999. Leuconostoc oenos and malolactic fermentation in wine: A review. Journal of Industrial Microbiology & Biotechnology 23:447-455.
7. Yang, D., and C. R. Woese. 1989. Phylogenetic structure of the Leuconostocs: An interesting case of a rapidly evolving organism. Systematic and Applied Microbiology 12:145-149.
8. Zuniga, M., I. Pardo, and S. Ferrer. 1996. Transposons Tn916 and Tn925 can transfer from Enterococcus faecalis to Leuconostoc oenos. FEMS Microbiology Letters 135:179-85.

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