Microbiology Doctoral Training Program, University of Wisconsin-Madison, Madison, Wisconsin, USA.
Department of Bacteriology, University of Wisconsin-Madison, Madison, Wisconsin, USA.
Appl Environ Microbiol. 2024 Nov 20;90(11):e0136224. doi: 10.1128/aem.01362-24. Epub 2024 Oct 22.
Type VII protein secretion systems play an important role in the survival and virulence of pathogens and in the competition among some microbes. Potential polymorphic toxin substrates of the type VII secretion system (T7SS) in are important for competition in the context of biofilm communities. Within a biofilm, there is significant physiological heterogeneity as cells within the population take on differential cell fates. Which cells express and deploy the various T7SS substrates is still unknown. To identify which cells express at least one of the T7SS substrates, we investigated the operon. The operon encodes at least one predicted T7SS substrate. Starting with an analysis of the operon promoter region, we identified potential regulatory sequences. Using a promoter-reporter fusion, we then identified several regulators that impact expression of the operon, including a regulator of biofilm formation, DegU. In a deletion mutant, expression is completely abolished. Mutation of predicted DegU binding sites also results in a significant reduction in reporter levels. Further analysis of regulation reveals that deletion of has the opposite effect of the deletion. Following the reporter by microscopy of cells harvested from biofilms, we find that the operon is expressed specifically in the subset of cells undergoing sporulation. Together, our results define cells entering sporulation as the subpopulation most likely to express products of the operon in .IMPORTANCEDifferential expression of genes in a bacterial community allows for the division of labor among cells in the community. The toxin substrates of the type VII secretions system (T7SS) are known to be active in biofilm communities. This work describes the expression of one of the T7SS-associated operons, the operon, which encodes the YFJ toxin, in the sporulating subpopulation within a biofilm. The evidence that the YFJ toxin may be deployed specifically in cells at the early stages of sporulation provides a potential role for deployment of T7SS in community-associated activities, such as cannibalism.
VII 型蛋白分泌系统在病原体的生存和毒力以及某些微生物之间的竞争中发挥着重要作用。在生物膜群落中，VII 型分泌系统（T7SS）的潜在多态性毒素底物对于竞争非常重要。在生物膜内，由于种群内的细胞承担不同的细胞命运，因此存在显著的生理异质性。哪些细胞表达和部署各种 T7SS 底物仍不得而知。为了确定哪些细胞至少表达一种 T7SS 底物，我们研究了 操纵子。 操纵子编码至少一种预测的 T7SS 底物。从 操纵子启动子区域的分析开始，我们确定了潜在的调控序列。然后，我们使用 启动子-报告基因融合来鉴定影响操纵子表达的几个调节剂，包括生物膜形成调节剂 DegU。在 缺失突变体中， 表达完全被废除。预测的 DegU 结合位点的突变也导致 报告基因水平显著降低。对 调控的进一步分析表明， 缺失的影响与 缺失的相反。通过对生物膜中收获的细胞进行显微镜观察 报告基因，我们发现 操纵子仅在经历孢子形成的细胞亚群中表达。总之，我们的结果将进入孢子形成的细胞定义为最有可能在 中表达 操纵子产物的亚群。重要的是，细菌群落中基因的差异表达允许群落中的细胞在劳动分工。VII 型分泌系统（T7SS）的毒素底物已知在生物膜群落中活跃。这项工作描述了 T7SS 相关操纵子之一的表达，即编码 YFJ 毒素的 操纵子，在生物膜中的孢子形成亚群中表达。YFJ 毒素可能专门在孢子形成的早期阶段的细胞中部署的证据为 T7SS 在社区相关活动中的部署提供了一个潜在的作用，例如同类相食。
