The multicellular behavior designated “red dry and rough” (rdar) morphotype—characterized by production of extracellular matrix mainly comprising curli fimbriae and cellulose—is a potential survival strategy of Escherichia coli outside the host. This study documents the ability of Escherichia cryptic clades, which have recently been recognized as new lineages genetically divergent from E. coli, to grow in unfavorable conditions through expression of distinct phenotypes. Growth under low-temperature and nutrient-poor conditions induced the rdar morphotype in all cryptic clade strains tested, especially after preincubation in broth supplemented with uracil. Such phenotypic response to harsh growth conditions was clearly detected by transmission and scanning electron microscopy, which showed that bacteria were encased in a fibrous matrix. Conversely, cells incubated in rich medium at 37 °C showed no matrix. Uracil enhanced the biosynthesis of matrix components, fostering biofilm production and strain adhesion to abiotic surfaces, as demonstrated by the increase of strong biofilm producers in biofilm assays. Harsh growth conditions also induced catalase activity, resulting in clade strain resistance to hydrogen peroxide oxidative stress. The present findings further support the ‘environmental hypothesis’ whereby cryptic clades would be able to persist in natural habitats outside the host through the expression of distinct survival phenotypes.

被称为“红色干和粗糙”（rdar）形态型的多细胞行为（通过产生主要包含卷曲菌毛和纤维素的细胞外基质来表征）是宿主以外大肠杆菌的潜在生存策略。这项研究记录了大肠埃希氏菌隐性进化枝的能力，这些进化枝最近被认为是从大肠杆菌遗传分化出的新谱系。，通过表达不同的表型在不利的条件下生长。在所有测试的隐性进化枝菌株中，在低温和营养缺乏的条件下生长会诱导rdar形态，特别是在添加了尿嘧啶的肉汤中预孵育后。通过透射和扫描电子显微镜清楚地检测到了对苛刻生长条件的这种表型反应，这表明细菌被包裹在纤维状基质中。相反，在37°C的富培养基中温育的细胞未显示任何基质。尿嘧啶增强了基质成分的生物合成，促进了生物膜的产生以及菌株对非生物表面的粘附，这通过生物膜测定法中强大的生物膜生产者的增加证明了这一点。苛刻的生长条件还诱导过氧化氢酶活性，导致进化枝菌株对过氧化氢的氧化胁迫具有抗性。