The accumulation of colibactin intermediates does not affect the growth and morphology of pks+Escherichia coli

Colibactin is a natural product made by numerous strains of E. coli that harbor the pks genomic island. The deletion of one of the genes within the pks island, the peptidase clbP, has been found to disrupt the maturation of colibactin, thus promoting the accumulation in the periplasmic space of numerous biosynthesis intermediates, some of which have been characterized chemically. To date, no one has reported the effect of such an accumulation of intermediates on the cellular morphology of the producing E. coli bacterium. In this report, we describe the scanning electron microscopy (SEM) images of numerous clinical isolates of E. coli harboring the pks island, collected from Puerto Rico hospitals. We have observed that the wild type isolates that harbor the pks island display lesions on the bacterial envelope surface. These lesions are absent in isolates lacking the pks island. To determine whether this phenotype is associated with colibactin production, we deleted the clbP gene from the extraintestinal pathogenic E. coli strain IHE3034, thus disrupting its ability to make colibactin. The wild-type IHE3034 displayed a spherical shape with no envelope lesions, and was practically indistinguishable from the {Delta}clbP deletion mutant. To our knowledge, this work provides the first SEM images of a pks deletion mutant. ImportanceThe pks genomic island has been linked to the promotion of DNA damage and colorectal cancer, through the production of genotoxic compound colibactin in some strains of E. coli. While much is known about the mechanism of colibactin toxicity once it enters the mammalian cell, the prior steps leading to colibactin secretion or translocation from the bacterial cell, remain unclear. Here, we report high-resolution electron microscopy images of E. coli IHE3034 strain, a known colibactin producer, and a deletion mutant that is known to accumulate colibactin intermediates. The images reveal a predominantly spherical morphology that is unaffected by the accumulation of colibactin precursors and intermediates.