Department of Medical Chemistry and Cell Biology, University of Gothenburg, Sweden.
Department of Medical Chemistry and Cell Biology, University of Gothenburg, Sweden.
Fish Shellfish Immunol. 2024 Oct;153:109862. doi: 10.1016/j.fsi.2024.109862. Epub 2024 Aug 28.
Aeromonas salmonicida is an opportunistic pathogen with relevance for aquaculture. Fish epithelia are covered by a mucus layer, composed mainly by highly glycosylated mucins, which are the first point of contact between fish and pathogens. Quorum sensing (QS), a bacterial communication mechanism through secreted autoinducer signals that governs gene expression, influences bacterial growth and virulence. The main A. salmonicida autoinducers are mediated by the luxS and asaI genes, corresponding to inter- and intraspecies communication, respectively. The aim of this study was to determine the effect of the mucins that pathogens encounter during colonization of the gill and skin on A. salmonicida QS. We found that expression of A. salmonicida asaI, but not luxS, was increased after culture at 20 °C compared to 10 °C. Rainbow trout gill and skin mucins up-regulated asaI expression 2-fold but down-regulated luxS 10-fold. The downregulation of luxS was reflected by a reduction in autoinducer-2 secretion. Mucins isolated from skin had a stronger inhibitory effect than mucins isolated from gills on both luxS expression and A1-2 secretion, consistent with a higher relative abundance of N-Acetylneuraminic acid on skin mucins than on gill mucins. Reduction of AI-2 production by mucins or luxS-deletion lead to a reduced A. salmonicida auto-aggregation. Furthermore, after colonization of the gill, luxS was down regulated whereas asaI expression was upregulated. Both in vivo and in vitro, the expression of luxS and asaI were thus differentially regulated, frequently in an inverse manner. The strong AI-2 inhibiting effect of the skin mucins is likely part of the mucin-based defense against pathogens.
嗜水气单胞菌是一种机会性病原体，与水产养殖有关。鱼类上皮细胞被一层黏液层覆盖，主要由高度糖基化的黏蛋白组成，这是鱼类与病原体接触的第一点。群体感应（QS）是一种通过分泌自动诱导信号的细菌通讯机制，控制基因表达，影响细菌生长和毒力。主要的嗜水气单胞菌自动诱导物由 luxS 和 asaI 基因介导，分别对应于种间和种内通讯。本研究旨在确定在鳃和皮肤定植过程中病原体遇到的黏液对嗜水气单胞菌 QS 的影响。我们发现，与 10°C 相比，20°C 培养后嗜水气单胞菌 asaI 的表达增加，但 luxS 的表达没有增加。虹鳟鱼鳃和皮肤黏液使 asaI 表达增加 2 倍，但使 luxS 表达减少 10 倍。luxS 的下调反映在自动诱导物-2 分泌减少。与从鳃中分离的黏液相比，从皮肤中分离的黏液对 luxS 表达和 A1-2 分泌的抑制作用更强，这与皮肤黏液中 N-乙酰神经氨酸的相对丰度高于鳃黏液一致。黏液或 luxS 缺失减少 AI-2 的产生导致嗜水气单胞菌自动聚集减少。此外，在鳃定植后，luxS 下调，而 asaI 表达上调。在体内和体外，luxS 和 asaI 的表达都因此受到不同的调节，通常是相反的方式。皮肤黏液对 AI-2 的强烈抑制作用可能是基于黏液的防御病原体的一部分。
