Discrepancies between the phenotypic and genotypic characterization of Lactococcus lactis cheese isolates.
OBJECTIVE
The use of randomly amplified polymorphic DNA (RAPD)-PCR fingerprinting and plasmid profiles to determine at the strain level, the similarity of Lactococcus lactis isolates obtained during sampling of traditional cheeses and to verify its correspondence to the selected phenotypic characteristics.


RESULTS
A total of 45 L. lactis isolates were genotypically analysed by RAPD-PCR fingerprinting and plasmid patterns. Phenotypic traits used to compare strains were proteolytic, acidifying, aminotransferase (aromatic and branched chain aminotransferase) and alpha-ketoisovalerate decarboxylase (Kivd) activities. The results show that 23 isolates could be grouped in clusters that exhibited 100% identity in both their RAPD and plasmid patterns, indicating the probable isolation of dominant strains during the cheese sampling process. However, there were phenotypic differences between isolates within the same cluster that included the loss of relevant technological properties such as proteinase activity and acidifying capacity or high variation in their amino acid converting enzyme activities. Likewise, the analysis of a specific attribute, Kivd activity, indicated that 7 of 15 isolates showed no detectable activity despite the presence of the encoding (kivd) gene.


CONCLUSIONS
Phenotypic differences found between genotypically similar strains of L. lactis strains could be linked to differences in enzymatic expression.


CONCLUSIONS
Phenotypic analysis of L. lactis isolates should be considered when selecting strains with new cheese flavour forming capabilities.
de la Plaza
M
M
Department of Dairy Science and Technology, Instituto del Frío (CSIC), Madrid, Spain.
Rodríguez
A
A
Fernández de Palencia
P
P
Martínez-Cuesta
M C
MC
Peláez
C
C
Requena
T
T
D000595:Amino Acid Sequence; D002611:Cheese / Q000382:microbiology*; D004269:DNA, Bacterial / Q000032:analysis*; D005511:Food Handling; D005516:Food Microbiology; D014644:Genetic Variation; D005838:Genotype; D013294:Lactococcus lactis / Q000145:classification / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification*; D008969:Molecular Sequence Data; D010641:Phenotype; D010802:Phylogeny; D019105:Random Amplified Polymorphic DNA Technique / Q000379:methods*; D017386:Sequence Homology, Amino Acid
D004269:DNA, Bacterial