Adherence and invasive properties of Corynebacterium diphtheriae strains correlates with the predicted membrane-associated and secreted proteome

Abstract

BackgroundNon-toxigenic Corynebacterium diphtheriae strains are emerging as a major cause of severe pharyngitis and tonsillitis as well as invasive diseases such as endocarditis, septic arthritis, splenic abscesses and osteomyelitis. C. diphtheriae strains have been reported to vary in their ability to adhere and invade different cell lines. To identify the genetic basis of variation in the degrees of pathogenicity, we sequenced the genomes of four strains of C. diphtheriae (ISS 3319, ISS 4060, ISS 4746 and ISS 4749) that are well characterised in terms of their ability to adhere and invade mammalian cells.ResultsComparative analyses of 20 C. diphtheriae genome sequences, including 16 publicly available genomes, revealed a pan-genome comprising 3,989 protein coding sequences that include 1,625 core genes and 2,364 accessory genes. Most of the genomic variation between these strains relates to uncharacterised genes encoding hypothetical proteins or transposases. Further analyses of protein sequences using an array of bioinformatic tools predicted most of the accessory proteome to be located in the cytoplasm. The membrane-associated and secreted proteins are generally involved in adhesion and virulence characteristics. The genes encoding membrane-associated proteins, especially the number and organisation of the pilus gene clusters (spa) including the number of genes encoding surface proteins with LPXTG motifs differed between different strains. Other variations were among the genes encoding extracellular proteins, especially substrate binding proteins of different functional classes of ABC transport systems and ‘non-classical’ secreted proteins.ConclusionsThe structure and organisation of the spa gene clusters correlates with differences in the ability of C. diphtheriae strains to adhere and invade the host cells. Furthermore, differences in the number of genes encoding membrane-associated proteins, e.g., additional proteins with LPXTG motifs could also result in variation in the adhesive properties between different strains. The variation in the secreted proteome may be associated with the degree of pathogenesis. While the role of the ‘non-classical’ secretome in virulence remains unclear, differences in the substrate binding proteins of various ABC transport systems and cytoplasmic proteins potentially suggest strain variation in nutritional requirements or a differential ability to utilize various carbon sources.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1980-8) contains supplementary material, which is available to authorised users.

Evolution, epidemiology and diversity of Corynebacterium diphtheriae : New perspectives on an old foe

“…Strains within STs appear to show close relationships indicating the robust nature of the MLST approach ( Fig. 2; Bolt et al, 2010;Sangal et al, 2015). Similar groupings were also obtained from the genome-wide single nucleotide polymorphism analysis (SNPs; Sangal et al, 2014aSangal et al, , 2014b.…”

“…The strains within individual STs differed from each other by the presence or absence of up to 290 genes, many of which are present on the genomic islands (Sangal et al, 2015). These observations indicate likely differences in recombination frequencies between C. diphtheriae strains.…”

“…diphtheriae strains have been analysed (Cerdeno-Tarraga et al, 2003;Sangal et al, 2015;Sangal et al, 2014aSangal et al, , 2014bSangal et al, , 2012aSangal et al, , 2012bTrost et al, 2012), revealing the genetic diversity among and within the major STs. Approximately 60% of the genome appears to be functionally conserved within C. diphtheriae strains with 1625 genes belonging to the core genome (Sangal et al, 2015). However, enough diversity has accumulated within the core genes to allow discrimination of most C. diphtheriae strains from each other.…”

“…Similar groupings were also obtained from the genome-wide single nucleotide polymorphism analysis (SNPs; Sangal et al, 2014aSangal et al, , 2014b. The accessory genome varied greatly among C. diphtheriae strains (Sangal et al, 2015) even when a relatively small number of genomes was considered (14 known STs; Fig. 1).…”

“…Approximately one-third of the C. diphtheriae genome encodes accessory genes that vary widely between strains (Sangal et al, 2015). The strains within individual STs differed from each other by the presence or absence of up to 290 genes, many of which are present on the genomic islands (Sangal et al, 2015).…”