Molecular cross-talk between Sa3int phages and their Stapylococcus aureus host

金黄色葡萄球菌是人类和动物的主要机会性病原体，无症状地定植于鼻腔，但也是危及生命的急慢性感染的主要原因。由于对不同宿主的短期和长期适应，物种的进化与噬菌体介导的染色体外移动元件和染色体标记物的转移密切相关。金黄色葡萄球菌菌株可携带多达四种温带噬菌体，其中许多噬菌体具有编码葡萄球菌毒力因子的辅助基因。超过90%的人鼻分离金黄色葡萄球菌被发现携带Sa3int噬菌体，该噬菌体作为前噬菌体整合到细菌的hlb基因中，从而破坏鞘磷脂酶hlb的表达，hlb是在某些感染条件下重要的毒力因子。在由大肠杆菌噬菌体携带的毒力因子编码基因中，有葡萄激酶、肠毒素、趋化抑制蛋白和/或葡萄球菌补体抑制剂，所有这些都是高度人类特异性的，可能是细菌在人类宿主中生存所必需的。因此，无论是将噬菌体插入细菌基因组还是从细菌基因组中切除，都有可能赋予金黄色葡萄球菌适应性优势。现在也有越来越多的证据表明，Sa3int噬菌体可能会进行“活性溶原”，在这一过程中，原噬菌体暂时从染色体上切除，而不会形成完整的噬菌体颗粒。然而，金黄色葡萄球菌宿主如何调节其温带噬菌体的生命周期在很大程度上仍然未知。我们的数据表明，参与细菌宿主与其噬菌体相互作用的细菌因子可能是菌株特异性的，某些金黄色葡萄球菌菌株比其他菌株更倾向于支持溶原性或溶性生命周期。我们的目的是破译调节Sa3int噬菌体从溶原到“活性溶原”或裂解期转变的分子机制。生物信息学分析将深入了解Sa3int噬菌体的多样性及其与某些金黄色葡萄球菌谱系的联系。将阐明参与溶原-“活性溶原”-溶解开关的噬菌体和细菌因子，并评估它们可能的相互作用。利用微流体装置在单细胞水平上监测溶原性、“活性溶原性”和噬菌体周期。这将有助于我们了解这些奇特的噬菌体是如何与它们的细菌宿主金黄色葡萄球菌一起进化的。

As a major opportunistic pathogen of human and animals Staphylococcus aureus asymptomatically colonizes the nasal cavity, but is also a leading cause of life-threatening acute and chronic infections. Evolution of the species as a result of short- and long-term adaptation to diverse hosts is tightly linked to phage-mediated transfer of extra-chromosomal mobile elements as well as chromosomal markers. S. aureus strains can carry up to four temperate phages, many of which possess accessory genes coding for staphylococcal virulence factors. More than 90% of the human nasal isolates of S. aureus were found to carry Sa3int phages, which integrate as prophages into the bacterial hlb gene thus disrupting the expression of the sphingomyelinase Hlb, an important virulence factor under certain infection conditions. Among the virulence factors-encoding genes carried by the ϕSa3-phages are staphylokinase, enterotoxins, chemotaxis-inhibitory proteins, and/or staphylococcal complement inhibitors, all of which are highly human-specific and probably essential for bacterial survival in the human host. Thus, both insertion of the prophages into and excision from the bacterial genome have the potential to confer a fitness advantage to S. aureus. There is now also growing evidence that Sa3int phages might perform “active lysogeny”, a process during which a prophage is temporally excised from the chromosome without forming intact phage particles. However, how the S. aureus host modulates the life cycle of its temperate phages remains largely unknown. Our data suggest that the bacterial factors supposedly involved in the interaction of the bacterial host with its phages are likely to be strain specific, with certain S. aureus strains being more prone than others to support either a lysogenic or a lytic life cycle. We aim to decipher the molecular mechanisms regulating the transition of Sa3int phages from a lysogenic to “active lysogenic” or to the lytic phase. Bioinformatic analyses will give insights into the diversity of Sa3int phages and their linkage to certain S. aureus linages. Phage and bacterial factors involved in the lysogenic-“active lysogenic”-lytic switch will be elucidated and their putative interactions assessed. Lysogeny, “active lysogeny” and lytic phage cycles will be monitored over time on the single cell level using microfluidic devices. This will help us understand how these peculiar phages have evolved together with their bacterial host S. aureus.