Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10979656 | Journal of Dairy Science | 2012 | 16 Pages |
Abstract
A collection of 17 natural lactococcal isolates from raw milk cheeses were studied in terms of their plasmid distribution, content, and diversity. All strains in the collection harbored an abundance of plasmids, including Lactococcus lactis ssp. cremoris DPC3758, whose 8-plasmid complement was selected for sequencing. The complete sequences of pAF22 (22,388Â kb), pAF14 (14,419Â kb), pAF12 (12,067Â kb), pAF07 (7,435Â kb), and pAF04 (3,801Â kb) were obtained, whereas gene functions of technological interest were mapped to pAF65 (65Â kb) and pAF45 (45Â kb) by PCR. The plasmids of L. lactis DPC3758 were found to encode many genes with the potential to improve the technological properties of dairy starters. These included 3 anti-phage restriction/modification (R/M) systems (1 of type I and 2 of type II) and genes for immunity/resistance to nisin, lacticin 481, cadmium, and copper. Regions encoding conjugative/mobilization functions were present in 6 of the 8 plasmids, including those containing the R/M systems, thus enabling the food-grade transfer of these mechanisms to industrial strains. Using cadmium selection, the sequential stacking of the R/M plasmids into a plasmid-free host provided the recipient with increased protection against 936- and c2-type phages. The association of food-grade selectable markers and mobilization functions on L. lactis DPC3758 plasmids will facilitate their exploitation to obtain industrial strains with enhanced phage protection and robustness. These natural plasmids also provide another example of the major role of plasmids in contributing to host fitness and preservation within its ecological niche.
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Authors
V. Fallico, R.P. Ross, G.F. Fitzgerald, O. McAuliffe,