Summary auto-generated
This study sequenced a 580 base-pair fragment of the mle gene, which encodes malolactic enzyme, from 13 strains of lactic acid bacteria spanning four genera: Pediococcus, Leuconostoc, Lactobacillus, and Oenococcus. The researchers constructed phylogenetic trees from these malolactic enzyme sequences and compared them with 16S rRNA gene trees. The malolactic enzyme sequences evolved more rapidly and showed different phylogenetic relationships than the 16S gene. While 16S rRNA trees grouped Pediococcus and Lactobacillus together, mle sequences separated these genera. Additionally, Leuconostoc mesenteroides and Oenococcus oeni, which were distinct in 16S rRNA trees, clustered with Lactobacillus species in the mle tree. Amino acid sequences from the malolactic enzyme fragments were compared with 22 malic enzyme sequences from various organisms. Malic and malolactic enzymes formed distinct phylogenetic groups, except yeast and E. coli malic enzymes clustered closer to malolactic enzymes. Analysis of conserved domains identified key amino acids specific to each enzyme type, particularly in metal-binding sites and substrate-binding regions.
Key findings
- Malolactic enzyme gene sequences evolved more rapidly and differently than 16S rRNA genes, producing different phylogenetic groupings of lactic acid bacteria
- Pediococcus and Lactobacillus species intermixed in mle trees but were separated in 16S rRNA trees, indicating mle sequences better resolve certain taxonomic relationships
- Leuconostoc mesenteroides and Oenococcus oeni positioned distinctly in 16S rRNA analysis but intermixed with Lactobacillus species in mle phylogenetic analysis
- Malic and malolactic enzymes are phylogenetically distinct, though yeast and E. coli malic enzymes cluster closer to malolactic enzymes than to other malic enzymes
- Critical amino acids in metal-binding sites are conserved between malic and malolactic enzymes, while key substitutions (cysteine to isoleucine, arginine to glycine) distinguish enzyme types
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Abstract
DNA sequences covering 36% of the mle gene that encodes the malolactic enzyme were determined for 13 strains of lactic acid bacteria, representing Pediococcus, Leuconostoc, Lactobacillus and Oenococcus genera. The sequences were aligned with the corresponding region of mleS in Lactococcus lactis. The phylogenetic distance matrix tree of all mle sequences was compared with the 16S rRNA phylogenetic tree. The analysis showed that the mle fragment evolved more rapidly than the 16S gene and differently. Pediococcus and Lactobacillus species were intermixed in the 16S rRNA tree whereas they were separated in the mle tree. Leuconostoc mesenteroides and Oenococcus oeni were distinct from other species in the 16S rRNA tree, whereas they were intermixed with Lactobacillus species and Lactococcus lactis in the mle tree. The amino acid sequences deduced from partial mle genes were aligned with 22 malic enzyme sequences and the corresponding phylogenetic tree was constructed. Malic and malolactic enzymes were distinct at the phylogenetic level, except for malic enzymes of yeast and Escherichia coli which were nearer the malolactic enzymes than the other malic enzymes. The analysis of conserved sites showed several interesting amino acids specific to either malic enzyme or malolactic enzyme.