Usage of gdpP for improved subspecies differentiation of Lactococcus lactis

摘要

Lactic acid bacteria (LABs), in particular Lactococcus lactis strains, are important for the production of fermented dairy products. Natural sources are interesting reservoirs of new strains with superior performance. Five LAB isolates from Algerian camel milk were characterized phenotypically, i.e. according to metabolic activities and growth characteristics, and by gene sequence-based methods. Phenotypically all isolates were identified as proteolytic Lactococcus lactis, able to utilize citrate and lactose and to grow at temperatures up to 45°C, they could not be differentiated at the subspecies level. Sequencing and analysis of their 16S rRNA identified three strains as belonging to L. lactis ssp. lactis, and two as L. lactisssp. cremoris. These results were confirmed by a novel approach, using the conserved, single-copy gdpP gene for complementary phylogenetic analysis. GdpP performed better than the 16S rRNA gene in resolving relationships as well as subtle differences at the subspecies level. The isolate HD20A was different from the other L. lactisssp. lactis strains, showing are combination event in its gdpP gene which proved to be a chimaera between the sequences typical for ssp. lactis and ssp. cremoris, respectively. This is another example for the importance of horizontal gene transfer in the evolution of Lactococcus lactis.