Distribution of Megaplasmids inLactobacillus salivariusand Other Lactobacilli

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Abstract
The genome ofLactobacillus salivariusUCC118 includes a 242-kb megaplasmid, pMP118. We now show that 33 strains ofL. salivariusisolated from humans and animals all harbor a megaplasmid, which hybridized with therepAandrepEreplication origin probes of pMP118. Linear megaplasmids that did not hybridize with the pMP118repAprobe were also found in some strains ofL. salivarius, showing for the first time that a lactic acid bacterium has multiple megaplasmids. Phylogenetic analysis of therepEandgroELsequences of 28L. salivariusstrains suggested similar evolutionary paths for the chromosome and megaplasmid. Although the replication origin of circular megaplasmids inL. salivariuswas highly conserved, genotypic and phenotypic comparisons revealed significant variation between megaplasmid-encoded traits. Furthermore, megaplasmids of sizes ranging from 120 kb to 490 kb were present in seven strains belonging to six otherLactobacillusspecies from among 91 strains and 47 species tested. The discovery of the widespread presence of megaplasmids inL. salivarius, and restricted carriage by otherLactobacillusspecies, provides an opportunity to study the contribution of large extrachromosomal replicons to the biology ofLactobacillus.