September 22, 2019  |  

Streptococcus suis contains multiple phase-variable methyltransferases that show a discrete lineage distribution.

Authors: Atack, John M and Weinert, Lucy A and Tucker, Alexander W and Husna, Asma U and Wileman, Thomas M and F Hadjirin, Nazreen and Hoa, Ngo T and Parkhill, Julian and Maskell, Duncan J and Blackall, Patrick J and Jennings, Michael P

Streptococcus suis is a major pathogen of swine, responsible for a number of chronic and acute infections, and is also emerging as a major zoonotic pathogen, particularly in South-East Asia. Our study of a diverse population of S. suis shows that this organism contains both Type I and Type III phase-variable methyltransferases. In all previous examples, phase-variation of methyltransferases results in genome wide methylation differences, and results in differential regulation of multiple genes, a system known as the phasevarion (phase-variable regulon). We hypothesized that each variant in the Type I and Type III systems encoded a methyltransferase with a unique specificity, and could therefore control a distinct phasevarion, either by recombination-driven shuffling between different specificities (Type I) or by biphasic on-off switching via simple sequence repeats (Type III). Here, we present the identification of the target specificities for each Type III allelic variant from S. suis using single-molecule, real-time methylome analysis. We demonstrate phase-variation is occurring in both Type I and Type III methyltransferases, and show a distinct association between methyltransferase type and presence, and population clades. In addition, we show that the phase-variable Type I methyltransferase was likely acquired at the origin of a highly virulent zoonotic sub-population.

Journal: Nucleic acids research
DOI: 10.1093/nar/gky913
Year: 2018

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