Discrepancies between the phenotypic and genotypic characterization

26 27 28 Aims: The use of RAPD-PCR fingerprinting and plasmid profiles to determine at the 29 strain level, the similarity of Lactococcus lactis isolates obtained during sampling of 30 traditional cheeses and to verify its correspondence to the selected phenotypic 31 characteristics. 32 Methods and Results: A total of 45 L. lactis isolates were genotypically analyzed by 33 RAPD-PCR fingerprinting and plasmid patterns. Phenotypic traits used to compare 34 strains were proteolytic, acidifying, aminotransferase (AraT, BcaT) and alpha35 ketoisovalerate decarboxylase (Kivd) activities. The results show that 23 isolates could 36 be grouped in clusters that exhibited 100% identity in both their RAPD and plasmid 37 patterns, indicating the probable isolation of dominant strains during the cheese 38 sampling process. However, there were phenotypic differences between isolates within 39 the same cluster that included the loss of relevant technological properties such as 40 proteinase activity and acidifying capacity or high variation in their amino acid 41 converting enzyme activities. Likewise, the analysis of a specific attribute, Kivd 42 activity, indicated that 7 out of 15 isolates showed no detectable activity despite the 43 presence of the encoding (kivd) gene. 44 Conclusion: Phenotypic differences found between genotypically similar strains of L. 45 lactis strains could be linked to differences in enzymatic expression. 46 Significance and Impact of Study: Phenotypic analysis of L. lactis isolates should be 47 considered when selecting strains with new cheese flavour forming capabilities. 48 49