The propensity of bacteria to grow collectively in communities known as biofilms and their ability to overcome clinical treatments in this condition has become a major medical problem, emphasizing the need for anti-biofilm strategies. Antagonistic microbial interactions have extensively served as searching platforms for antibiotics, but their potential as sources for anti-biofilm compounds has barely been exploited. By screening for microorganisms that in agar-set pairwise interactions could antagonize Escherichia coli’s ability to form macrocolony biofilms, we found that the soil bacterium Bacillus subtilis strongly inhibits the synthesis of amyloid fibers –known as curli-, which are the primary extracellular matrix (ECM) components of E. coli biofilms. We identified bacillaene, a B. subtilis hybrid non-ribosomal peptide/polyketide metabolite, previously described as a bacteriostatic antibiotic, as the effector molecule. We found that bacillaene combines both antibiotic and anti-curli functions in a concentration-dependent order that potentiates the ecological competitiveness of B. subtilis, highlighting bacillaene as a metabolite naturally optimized for microbial inhibition. Our studies revealed that bacillaene inhibits curli by directly impeding the assembly of the CsgB and CsgA curli subunits into amyloid fibers. Moreover, we found that curli inhibition occurs despite E. coli attempts to reinforce its protective ECM by inducing curli genes via a RpoS-mediated competition sensing response trigged by the threatening presence of B. subtilis. Overall, our findings illustrate the relevance of exploring microbial interactions not only for finding compounds with unknown and unique activities, but for uncovering additional functions of compounds previously categorized as antibiotics.

细菌在被称为生物膜的群落中集体生长的倾向以及它们在这种情况下克服临床治疗的能力已成为一个主要的医学问题，强调了抗生物膜策略的必要性。拮抗微生物相互作用已广泛用作抗生素的搜索平台，但它们作为抗生物膜化合物来源的潜力几乎没有被开发。通过筛选在琼脂组中成对相互作用可以拮抗大肠​​杆菌形成大菌落生物膜能力的微生物，我们发现土壤细菌枯草芽孢杆菌强烈抑制淀粉样纤维（称为curli）的合成，淀粉样纤维是主要的细胞外基质（ECM） ）大肠杆菌生物膜的成分。我们将枯草芽孢杆菌杂合非核糖体肽/聚酮化合物代谢物bacillaene 确定为效应分子，之前被描述为抑菌抗生素。我们发现芽孢杆菌烯以浓度依赖的顺序结合了抗生素和抗卷曲功能，增强了枯草芽孢杆菌的生态竞争力，突出了芽孢杆菌烯作为一种天然优化的微生物抑制代谢物。我们的研究表明，bacillaene 通过直接阻止 CsgB 和 CsgA curli 亚基组装成淀粉样蛋白纤维来抑制 curli。此外，我们发现，尽管大肠杆菌试图通过由枯草芽孢杆菌的威胁性存在触发的 RpoS 介导的竞争感应反应诱导 curli 基因来增强其保护性 ECM，但还是发生了 curli抑制。总体而言，我们的研究结果说明了探索微生物相互作用的相关性，不仅可以寻找具有未知和独特活性的化合物，而且可以发现先前归类为抗生素的化合物的其他功能。