Mosaic-like sequences containing transposon, phage, and plasmid elements among Listeria monocytogenes plasmids

Abstract

Sequencing of plasmid pLM33 from the food isolate Listeria monocytogenes Lm1 revealed a molecule of 32,307 bp with a G+C content of 36.2%. The plasmid displays a mosaic pattern of identities common to several closely related L. monocytogenes plasmids isolated from food and clinical sources.

FIG. 1.

Comparative analyses of Listeria plasmid genomes. Panel A shows the dot plot matrix calculated for the complete sequences of pLM33, pJ1-194, pN1-017, pR2-503, pF2-515, pCT100, pLI100, and pLM80. Panel B depicts a circular plot of genome diversity in Listeria plasmids. Each ring indicates a Listeria plasmid; the order is shown within the inner circle of the figure.

FIG. 2.

Phylogenetic relationship analysis of Listeria plasmids. The trees were constructed by maximum likelihood (program PHYML, bootstrap 100, HKY +G model) using DNA sequences of putative replication proteins in the plasmids (A) and UPGMA of pairwise distances calculated as the logarithm of shared orthologs (cutoffs, 30% identity, E value of 1 × 10⁻⁶, and a match of over 80% of both proteins) between two plasmid genomes, normalized by the weighted mean of the total number of plasmid genes (12) (B). The tree was built using MEGA4 software (28).

FIG. 3.

Genetic structure of pLM33 (A) and its homology with sequences of other L. monocytogenes plasmids (B). In panel A, the black circle represents the GC content and the green and purple circles represent the GC skew. In panel B, the same filling patterns indicate homologous sequences with an identity of >98%.