Genetic variability of mutans streptococci revealed by wide whole-genome sequencing

Lifu Song,Helena Sztajer,An-Ping Zeng,Georg Conrads,Irene Wagner-Döbler,Wei Wang,Anke Rheinberg,Michael Reck

doi:10.1186/1471-2164-14-430

Abstract

BackgroundMutans streptococci are a group of bacteria significantly contributing to tooth decay. Their genetic variability is however still not well understood.ResultsGenomes of 6 clinical S. mutans isolates of different origins, one isolate of S. sobrinus (DSM 20742) and one isolate of S. ratti (DSM 20564) were sequenced and comparatively analyzed. Genome alignment revealed a mosaic-like structure of genome arrangement. Genes related to pathogenicity are found to have high variations among the strains, whereas genes for oxidative stress resistance are well conserved, indicating the importance of this trait in the dental biofilm community. Analysis of genome-scale metabolic networks revealed significant differences in 42 pathways. A striking dissimilarity is the unique presence of two lactate oxidases in S. sobrinus DSM 20742, probably indicating an unusual capability of this strain in producing H2O2 and expanding its ecological niche. In addition, lactate oxidases may form with other enzymes a novel energetic pathway in S. sobrinus DSM 20742 that can remedy its deficiency in citrate utilization pathway.Using 67 S. mutans genomes currently available including the strains sequenced in this study, we estimates the theoretical core genome size of S. mutans, and performed modeling of S. mutans pan-genome by applying different fitting models. An “open” pan-genome was inferred.ConclusionsThe comparative genome analyses revealed diversities in the mutans streptococci group, especially with respect to the virulence related genes and metabolic pathways. The results are helpful for better understanding the evolution and adaptive mechanisms of these oral pathogen microorganisms and for combating them.

Highlights

Mutans streptococci are a group of bacteria significantly contributing to tooth decay
Traditionally and supported by 16S rRNA gene and rnpB gene sequence analyses, the genus Streptococcus is divided into several groups, with the mutans group streptococci consisting of the species S. mutans, S. sobrinus, S. ratti, S. criceti, S. downei, S. macacae, and – but controversially discussed – S. ferus [1]
An overview of the genome assemblies and annotations of the 6 S. mutans isolates as well as S. ratti DSM 20564 and S. sobrinus DSM 20742 is summarized in Table 1 in comparison with two previously sequenced S. mutans strains, namely UA159 and S. mutans NN2025

Summary

Introduction

Mutans streptococci are a group of bacteria significantly contributing to tooth decay. Their genetic variability is still not well understood. With the rapid development of DNA sequencing technologies, the steadily increasing genome data enable us to dig the evolutionary and genetic information of a species from a pan-genome perspective. In 2002, the release of the genome sequence of S. mutans UA159, the first genome sequence of mutans group streptococci, has greatly helped in understanding the robustness and complexity of S. mutans as an oral and odontogenic (e.g. infective endocarditis and abscesses) pathogen [8]. After the genome sequence of S. mutans NN2025 became available, a comparative genomic analysis of S. mutans NN2025 and UA159 provides insights into chromosomal shuffling and species-specific contents [9]. Cornejo et al have studied the evolutionary and population genomics of S. mutans based on 57 S. mutans draft genomes and revealed a high lateral gene transfer (LGT) rate of S. mutans [10]

Methods

Results

Conclusion