Abstract
Streptococcus suis is a porcine commensal and pathogen with zoonotic potential. We recently identified a novel Type I restriction–modification (R–M) system in a zoonotic S. suis clone which has emerged in the Netherlands. Here, we describe the DNA inversions in the specificity subunit of this system in S. suis serotype 2, clonal complex 20 and explain the absence of domain movement by the absence of repeats. In addition, we identified a core Type I R–M system present in 95% of the isolates and found an association of the distribution of Type I R–M systems in the S. suis genome with population structure. We speculate on the potential role of Type I R–M systems in S. suis given the recently described associations of Type I R–M systems with virulence and propose future research directions.
Highlights
Restriction–modification (R–M) systems are protein complexes which protect the host bacterium from invasion by foreign DNA through global methylation by methyltransferase (MTase) activity and digestion of the invaded DNA by restriction endonuclease (REase) activity [1]
We sequenced 116 S. suis isolates from the Netherlands and performed a whole genome analysis to search for genetic factors important for zoonotic potential [9]
The single S. suis serotype causing zoonotic infection in the Netherlands is serotype 2, which belongs to either multi-locus sequence type (MLST) clonal complex (CC) 1 or CC20 [14]
Summary
Restriction–modification (R–M) systems are protein complexes which protect the host bacterium from invasion by foreign DNA through global methylation by methyltransferase (MTase) activity and digestion of the invaded DNA by restriction endonuclease (REase) activity [1]. Each individual TRD can be exchanged, resulting in different TRD combinations, allowing for a great variety of R–M specificities. Both the MTase complexes as well as the REase complex make use of the same S subunit, which creates an efficient system for switching the R–M specificity of the host cell. The different combinations of TRDs in S subunits result in different global methylation patterns of the host DNA, which in turn may have an impact on global gene expression.
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