State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu Province, China.
School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu Province, China.
J Appl Microbiol. 2022 Oct;133(4):2122-2136. doi: 10.1111/jam.15446. Epub 2022 Jan 25.
Hexanal and geraniol are essential oil components with anti-quorum sensing (QS) activity against Pseudomonas fluorescens. This study demonstrated that QS inhibition (QSI) efficacy of the hexanal and geraniol combination (HG) was significantly higher when compared to those of their mono-counterparts at the same concentration.
Tests on P. fluorescens motility, biofilm formation, acyl-homoserine lactones' (AHLs) production, gene expression in vitro, and molecular docking in silico were conducted to evaluate the synergistic effect of hexanal and geraniol on QSI. HG mixture at 0.5 minimal inhibitory concentration (MIC) showed a strong synergistic inhibition of biofilm formation (51.8%), motility (60.13%), and extracellular protease activity (58.9%) of P. fluorescens. The synthesis of AHLs, e.g., C -HSL and C -HSL, was inhibited by hexanal, geraniol, and HG; both AHLs are responsible for regulating virulence factors in P. fluorescens. The expression of pcoI and gacA genes regulating AHL synthetase and sensor kinase was significantly down-regulated by HG (0.29 and 0.38-fold) at 0.5 MIC. Hexanal and HG showed significant inhibition of the expression of pcoR and gacS genes, which are responsible for AHL receptor protein and response regulation; however, geraniol failed to downregulate the two genes. Molecular docking in silico also supported these findings. Hexanal, which gets inserted into the minor groove of pcoI/pcoR DNA fragments, inhibits the expression of both the genes. Both hexanal (-31.487 kcal/mol) and geraniol (-25.716 kcal/mol) had a higher binding affinity with PcoI protein than the halogenated furanone C30 (-24.829 kcal/mol), which is a known competitor of AHLs. Similarly, hexanal and geraniol strongly bind to the PcoR protein also.
It was found that HG at 0.5 MIC could effectively inhibit QS by suppressing the expression of pcoR/gacS and gacA/gacS genes and therefore, could inhibit the motility and biofilm formation of P. fluorescens.
The present study indicated that HG at sub-MIC as QS inhibitor could be further developed as a new preservative of agri-food products.
己醛和香叶醇是具有抗群体感应（QS）活性的精油成分，可抑制荧光假单胞菌。本研究表明，与单一组分相比，相同浓度下己醛和香叶醇混合物（HG）的 QS 抑制（QSI）效果明显更高。
通过体外测试荧光假单胞菌的运动性、生物膜形成、酰基高丝氨酸内酯（AHLs）的产生、基因表达以及分子对接，评估了己醛和香叶醇对 QSI 的协同作用。HG 混合物在 0.5 最小抑菌浓度（MIC）下对荧光假单胞菌的生物膜形成（51.8%）、运动性（60.13%）和细胞外蛋白酶活性（58.9%）表现出强烈的协同抑制作用。己醛、香叶醇和 HG 抑制了 C-HSL 和 C-HSL 等 AHL 的合成，这些 AHL 负责调节荧光假单胞菌中的毒力因子。HG（0.29 和 0.38 倍）在 0.5 MIC 时显著下调了调节 AHL 合成酶和传感器激酶的 pcoI 和 gacA 基因的表达。HG 还显著抑制了负责 AHL 受体蛋白和反应调节的 pcoR 和 gacS 基因的表达，但香叶醇未能下调这两个基因。分子对接的计算机模拟也支持了这些发现。己醛插入 pcoI/pcoR DNA 片段的小沟中，抑制了两个基因的表达。与卤代呋喃酮 C30（-24.829 kcal/mol）相比，己醛（-31.487 kcal/mol）和香叶醇（-25.716 kcal/mol）对 PcoI 蛋白具有更高的结合亲和力，而 C30 是 AHLs 的已知竞争者。同样，己醛和香叶醇也能强烈结合 PcoR 蛋白。
研究发现，HG 在 0.5 MIC 时可通过抑制 pcoR/gacS 和 gacA/gacS 基因的表达有效抑制 QS，从而抑制荧光假单胞菌的运动性和生物膜形成。
本研究表明，HG 作为亚 MIC 浓度的 QS 抑制剂，可进一步开发为农业食品产品的新型防腐剂。
