Roy David, Takamatsu Daisuke, Okura Masatoshi, Goyette-Desjardins Guillaume, Van Calsteren Marie-Rose, Dumesnil Audrey, Gottschalk Marcelo, Segura Mariela
Faculty of Veterinary Medicine, Swine and Poultry Infectious Disease Research Centre, University of Montreal, Saint-Hyacinthe, QC, Canada.
Division of Bacterial and Parasitic Diseases, National Institute of Animal Health, National Agriculture and Food Research Organization, Tsukuba, Japan.
Front Microbiol. 2018 Apr 3;9:545. doi: 10.3389/fmicb.2018.00545. eCollection 2018.
The capsular polysaccharide (CPS) represents a key virulence factor for most encapsulated streptococci. and Group B (GBS) are both well-encapsulated pathogens of clinical importance in veterinary and/or human medicine and responsible for invasive systemic diseases. and GBS are the only Gram-positive bacteria which express a sialylated CPS at their surface. An important difference between these two sialylated CPSs is the linkage between the side-chain terminal galactose and sialic acid, being α-2,6 for but α-2,3 for GBS. It is still unclear how sialic acid may affect CPS production and, consequently, the pathogenesis of the disease caused by these two bacterial pathogens. Here, we investigated the role of sialic acid and the putative effect of sialic acid linkage modification in CPS synthesis using inter-species allelic exchange mutagenesis. To this aim, a new molecular biogenetic approach to express CPS with modified sialic acid linkage was developed. We showed that sialic acid (and its α-2,6 linkage) is crucial for CPS synthesis, whereas for GBS, CPS synthesis may occur in presence of an α-2,6 sialyltransferase or in absence of sialic acid moiety. To evaluate the effect of the CPS composition/structure on sialyltransferase activity, two distinct capsular serotypes within each bacterial species were compared ( serotypes 2 and 14 and GBS serotypes III and V). It was demonstrated that the observed differences in sialyltransferase activity and specificity between and GBS were serotype unrestricted. This is the first time that a study investigates the interspecies exchange of capsular sialyltransferase genes in Gram-positive bacteria. The obtained mutants represent novel tools that could be used to further investigate the immunomodulatory properties of sialylated CPSs. Finally, in spite of common CPS structural characteristics and similarities in the loci, sialic acid exerts differential control of CPS expression by and GBS.
荚膜多糖（CPS）是大多数有荚膜链球菌的关键毒力因子。A群链球菌（GAS）和B群链球菌（GBS）都是在兽医和/或人类医学中具有临床重要性的高度有荚膜的病原体，可引起侵袭性全身性疾病。GAS和GBS是仅有的在其表面表达唾液酸化CPS的革兰氏阳性细菌。这两种唾液酸化CPS之间的一个重要区别是侧链末端半乳糖与唾液酸之间的连接，GAS为α-2,6连接，而GBS为α-2,3连接。目前仍不清楚唾液酸如何影响CPS的产生，进而影响这两种细菌病原体所引起疾病的发病机制。在此，我们利用种间等位基因交换诱变研究了唾液酸的作用以及唾液酸连接修饰在CPS合成中的假定效应。为此，开发了一种新的分子生物发生方法来表达具有修饰唾液酸连接的CPS。我们发现唾液酸（及其α-2,6连接）对GAS的CPS合成至关重要，而对于GBS，在存在α-2,6唾液酸转移酶或不存在唾液酸部分的情况下都可能发生CPS合成。为了评估CPS组成/结构对唾液酸转移酶活性的影响，比较了每个细菌物种内的两种不同荚膜血清型（GAS血清型2和14以及GBS血清型III和V）。结果表明，观察到的GAS和GBS之间唾液酸转移酶活性和特异性的差异不受血清型限制。这是首次在革兰氏阳性细菌中研究荚膜唾液酸转移酶基因的种间交换。获得的突变体代表了可用于进一步研究唾液酸化CPS免疫调节特性的新工具。最后，尽管CPS具有共同的结构特征且GAS和GBS的相关基因座存在相似性，但唾液酸对GAS和GBS的CPS表达发挥着不同的调控作用。
