Loss of Plasmid-Mediated Oligopeptide Transport System in Lactococci: Another Reason for Slow Milk Coagulation |
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| Authors: | Weizhu Yu Kevin Gillies Jeffery K Kondo Jeffery R Broadbent Larry L McKay |
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| Institution: | aDepartment of Food Science and Nutrition, University of Minnesota, 1334 Eckles Avenue, St. Paul, Minnesota, 55108;bRhone-Poulenc, Marschall Products, 601 Science Drive, Madison, Wisconsin, 53711;cQuest International, 2402 7th Street N.W. Rochester, Minnesota, 55901;dDepartment of Nutrition and Food Sciences, Utah State University, Logan, Utah, 84322 |
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| Abstract: | Fast milk-coagulating (Fmc+) strains of lactococci are known to segregate slow milk-coagulating (Fmc−) variants, which has been attributed to loss of proteinase (Prt) activity encoded by plasmid DNA. It was found that the Fmc−phenotype could also be due to loss of a plasmid encoding an oligopeptide permease (Opp) system. InLactococcus lactissubsp.lactis(L. lactis) C2O, lactose metabolism (Lac) and Prt were linked to pJK550 and the Opp system to pJK430. InLactococcus lactissubsp.cremorisSK11, known to possess Prt on a 78-kb plasmid, DNA sequence analysis of a 7.4-kb region from the Lac plasmid, pSK11L, revealed that it possessed the Opp system. The Lac plasmid inL. lactisC2 encoded both the Prt and Opp systems. Fmc−derivatives ofL. lactisC2 were missing theprtgenes and had Opp integrated into the chromosome, possibly due to transposition events. Growth studies showed the Opp systems were functional and, in combination with Prt, produced the Fmc+phenotype. |
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