Sacher Jessica C, Shajahan Asif, Butcher James, Patry Robert T, Flint Annika, Hendrixson David R, Stintzi Alain, Azadi Parastoo, Szymanski Christine M
Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada.
Complex Carbohydrate Research Center, University of Georgia, Athens, GA, United States.
Front Microbiol. 2020 Mar 20;11:397. doi: 10.3389/fmicb.2020.00397. eCollection 2020.
Many bacterial pathogens display glycosylated surface structures that contribute to virulence, and targeting these structures is a viable strategy for pathogen control. The foodborne pathogen expresses a vast diversity of flagellar glycans, and flagellar glycosylation is essential for its virulence. Little is known about why encodes such a diverse set of flagellar glycans, but it has been hypothesized that evolutionary pressure from bacteriophages (phages) may have contributed to this diversity. However, interactions between phages and host flagellar glycans have not been characterized in detail. Previously, we observed that Gp047 (now renamed FlaGrab), a conserved phage protein, binds to flagella displaying the nine-carbon monosaccharide 7-acetamidino-pseudaminic acid, and that this binding partially inhibits cell growth. However, the mechanism of this growth inhibition, as well as how might resist this activity, are not well-understood. Here we use RNA-Seq to show that FlaGrab exposure leads 11168 cells to downregulate expression of energy metabolism genes, and that FlaGrab-induced growth inhibition is dependent on motile flagella. Our results are consistent with a model whereby FlaGrab binding transmits a signal through flagella that leads to retarded cell growth. To evaluate mechanisms of FlaGrab resistance in , we characterized the flagellar glycans and flagellar glycosylation loci of two strains naturally resistant to FlaGrab binding. Our results point toward flagellar glycan diversity as the mechanism of resistance to FlaGrab. Overall, we have further characterized the interaction between this phage-encoded flagellar glycan-binding protein and , both in terms of mechanism of action and mechanism of resistance. Our results suggest that encodes as-yet unidentified mechanisms for generating flagellar glycan diversity, and point to phage proteins as exciting lenses through which to study bacterial surface glycans.
许多细菌病原体都具有糖基化的表面结构，这些结构有助于其致病，针对这些结构是控制病原体的一种可行策略。食源性病原体表达种类繁多的鞭毛聚糖，鞭毛糖基化对其致病性至关重要。关于该病原体为何编码如此多样的鞭毛聚糖知之甚少，但据推测，来自噬菌体的进化压力可能促成了这种多样性。然而，噬菌体与宿主鞭毛聚糖之间的相互作用尚未得到详细表征。此前，我们观察到一种保守的噬菌体蛋白Gp047（现重新命名为FlaGrab）可与展示九碳单糖7-脒基-假氨基糖酸的该病原体鞭毛结合，且这种结合会部分抑制细胞生长。然而，这种生长抑制的机制以及该病原体如何抵抗这种活性尚不清楚。在这里，我们使用RNA测序表明，暴露于FlaGrab会导致该病原体细胞下调能量代谢基因的表达，并且FlaGrab诱导的生长抑制依赖于能动的鞭毛。我们的结果与一个模型一致，即FlaGrab结合通过鞭毛传递信号，导致细胞生长迟缓。为了评估该病原体对FlaGrab的抗性机制，我们对两种天然抗FlaGrab结合的该病原体菌株的鞭毛聚糖和鞭毛糖基化位点进行了表征。我们的结果表明鞭毛聚糖多样性是对FlaGrab抗性的机制。总体而言，我们进一步表征了这种噬菌体编码的鞭毛聚糖结合蛋白与该病原体之间在作用机制和抗性机制方面的相互作用。我们的结果表明，该病原体编码了尚未确定的产生鞭毛聚糖多样性的机制，并指出噬菌体蛋白是研究细菌表面聚糖的令人兴奋的切入点。
