The Six Faces of Streptococcus pneumoniae

Since the first paper describing the phenotypes of pneumococcus was published in 1933, bacteriologists have known that it is able to change forms (and with it, disease severity); but the way in which it does so have remained a mystery. Until now. An international team of researchers has discovered that the bacteria can take a staggering six different forms depending on the methylation status of its DNA, meaning that scientists who thought they were working on one bacteria may now be surprised to learn that, in effect, they’ve been studying six different ones.

Published in Nature Communications, the study describes how the team created mutant strains of the bacteria, each expressing one of six possible variants of the gene hsdS, which codes for a restriction modification system able to mediate gene expression via methylation (1). “Pneumococcus is an ideal organism, which is highly amenable to genetic manipulation, and models of pathogenesis are well described, so this study was fairly straightforward for us. Even so, finding a clear cut correlation of epigenetic control to carriage and invasive disease was a very positive surprise,” says lead author Marco Oggioni.

The team found that each of these six subpopulations has a different DNA methylation pattern, differences in gene expression and, based on experimental infection of mice, its own pathogenicity. Oggioni believes this work represents a paradigm shift in the understanding of bacterial gene regulation; one which will completely change the way in which S. pneumoniae is studied; “Researchers will have to control the methylation state of the bacteria they are working with, because it determines such strong differences. Work on this pathogen, and many other bacteria which appear to have this same type of epigenetic control, will have to change significantly. It goes without saying that pharmaceutical companies evaluating in vitro vaccine efficacy will also have to check the methylation profile,” he says.

The team now hopes to further investigate how changes in methylation affect gene expression; the exact mechanisms remain unclear. They also plan to investigate what effects the system has on human disease and infection, as their discovery may have far reaching implications for the treatment and prevention of pneumonia.

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References

1. A. S. Manso et al., “A Random Six-Phase Switch Regulates Pneumococcal Virulence Via Global Epigenetic Changes”, Nat. Commun., 5, [epub ahead of print] (2014). DOI: 10.1038/ncomms6055

About the Author(s)

Roisin McGuigan

I have an extensive academic background in the life sciences, having studied forensic biology and human medical genetics in my time at Strathclyde and Glasgow Universities. My research, data presentation and bioinformatics skills plus my ‘wet lab’ experience have been a superb grounding for my role as an Associate Editor at Texere Publishing. The job allows me to utilize my hard-learned academic skills and experience in my current position within an exciting and contemporary publishing company.

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