Department of Food and Animal Biotechnology, Seoul, Korea.
Mol Microbiol. 2012 Oct;86(2):411-25. doi: 10.1111/j.1365-2958.2012.08202.x. Epub 2012 Aug 29.
As natural killers of bacteria, bacteriophages have forced bacteria to develop a variety of defence mechanisms. The alteration of host receptors is one of the most common bacterial defence strategies against phage infection, which completely blocks phage attachment but comes at a potential fitness cost to the bacteria. Here, we report the cost-free, transient emergence of phage resistance in Salmonella enterica subspecies enterica serovar Typhimurium through a phase-variable modification of the O-antigen. Phage SPC35 typically requires BtuB as a host receptor but also uses the Salmonella O12-antigen as an adsorption-assisting apparatus for the successful infection of S. Typhimurium. The α-1,4-glucosylation of galactose residues in the O12-antigen by phase variably expressed O-antigen glucosylating genes, designated the (LT) (2) gtrABC1 cluster, blocks the adsorption-assisting function of the O12-antigen. Consequently, it confers transient SPC35 resistance to Salmonella without any mutations to the btuB gene. This temporal switch-off of phage adsorption through phase-variable antigenic modification may be widespread among Gram-negative bacteria-phage systems.
作为细菌的天然杀手，噬菌体迫使细菌产生了多种防御机制。改变宿主受体是细菌对抗噬菌体感染的最常见防御策略之一，这种策略完全阻止了噬菌体的附着，但对细菌的适应性有潜在的代价。在这里，我们通过 O 抗原的相变异构修饰报告了鼠伤寒沙门氏菌亚种肠炎沙门氏菌中无成本、短暂出现的噬菌体抗性。噬菌体 SPC35 通常需要 BtuB 作为宿主受体，但也利用沙门氏菌 O12 抗原作为吸附辅助装置，成功感染 S. 鼠伤寒沙门氏菌。相变异构表达的 O 抗原糖基化基因（命名为（LT）(2)gtrABC1 簇）将 O12 抗原中半乳糖残基的 α-1,4-葡糖苷化，阻断了 O12 抗原的吸附辅助功能。因此，它赋予沙门氏菌对 SPC35 的短暂抗性，而无需对 btuB 基因进行任何突变。通过相变异构抗原修饰暂时关闭噬菌体吸附作用可能在革兰氏阴性细菌-噬菌体系统中广泛存在。
