Comparison of plasmids from clinical Lactobacillus strains
Lyle Keenan , Harris
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The vaginal mucosa is dominated by Gram positive, rod shaped lactobacilli which serve as a natural barrier against infection. In both healthy and BV infected women Lactobacillus crispatus and Lactobacillus jensennii has been found to be the predominant Lactobacillus species. Many studies have been conducted to assess factors influencing lactobacilli dominance in the vaginal microbiome. However, no study has evaluated the impact of plasmids on the vaginal lactobacilli. In the present study two plasmids, pLc17 and pLc4, isolated from vaginal Lactobacillus species of both healthy and BV infected women were characterized. pLc4 was present in both Lactobacillus crispatus and Lactobacillus jensennii while pLc17 was only present in Lactobacillus crispatus. pLc17 (16663 bp in size) encoded a ribonucleotide diphosphate reductase (RNR), a filamentation induced by cAMP-like (FIC-like) protein and numerous mobile elements. The FIC-like protein may assist pLc17 to persist within the bacterial population, while RNR is commonly associated with phages and may indicate phage infection. pLc4 (4224 bp in size) encodes for a replication initiator protein and a plasmid partitioning protein. The replication protein on pLc4 shows 44% identity with the replication initiation protein of pSMQ173b_03. On further phylogenetic and sequence analysis with other Rolling Circle Replication (RCR) plasmids, pLc4 appears to be novel as the plasmid shows a low degree of similarity to these RCR plasmids. pLc17 appears to carry both a RCR replicon as well as a theta replicon, similar to pIP501, the broad-host-range plasmid from Bacillus subtilis. The relative Plasmid Copy Number (PCN) for pLc4 and pLc17 was analysed using quantitative polymerase chain reaction (qPCR) for the healthy state relative to the disease state from twentyeight vaginal swab samples obtained from the National Institute for Communicable Diseases (NICD). The relative PCN for pLc4 and pLc17 had a fold increase of ~2.803 and ~1.693, respectively in the healthy patient samples relative to BV infected patient samples. However, there were not found to be significant differences when taking the standard error into account Due to the novelty of these plasmids further analysis and characterisation is required for both plasmids, to establish what role they may play in the health of the vaginal milieu.