Oligosaccharides increase the genotoxic effect of colibactin produced by pks+ Escherichia coli strains

Abstract

Background Colibactin is a genotoxin that induces DNA double-strand breaks that may lead to carcinogenesis and is produced by Escherichia coli strains harboring the pks island. Human and animal studies have shown that colibactin-producing gut bacteria promote carcinogenesis and enhance the progression of colorectal cancer through cellular senescence and chromosomal abnormalities. In this study, we investigated the impact of prebiotics on the genotoxicity of colibactin-producing E. coli strains Nissle 1917 and NC101. Methods Bacteria were grown in medium supplemented with 20, 30 and 40 mg/mL of prebiotics inulin or galacto-oligosaccharide, and with or without 5 μM, 25 μM and 125 μM of ferrous sulfate. Colibactin expression was assessed by luciferase reporter assay for the clbA gene, essential for colibactin production, in E. coli Nissle 1917 and by RT-PCR in E. coli NC101. The human epithelial colorectal adenocarcinoma cell line, Caco-2, was used to assess colibactin-induced megalocytosis by methylene blue binding assay and genotoxicity by γ-H2AX immunofluorescence analysis. Results Inulin and galacto-oligosaccharide enhanced the expression of clbA in pks+ E. coli. However, the addition of 125 μM of ferrous sulfate inhibited the expression of clbA triggered by oligosaccharides. In the presence of either oligosaccharide, E. coli NC101 increased dysplasia and DNA double-strand breaks in Caco-2 cells compared to untreated cells. Conclusion Our results suggest that, in vitro, prebiotic oligosaccharides exacerbate DNA damage induced by colibactin-producing bacteria. Further studies are necessary to establish whether oligosaccharide supplementation may lead to increased colorectal tumorigenesis in animal models colonized with pks+ E. coli.

Somatic mutation rates scale with lifespan across mammals

“…This revealed a significant depletion of colibactin mutagenesis in the non-human crypts studied (Fisher's exact tests, P=7×10 -14 ). The apparent difference in colibactin mutagenesis observed between species, or between the cohorts studied, might result from a different prevalence of pks+ E. coli strains 42 or a different expression of colibactin by pks+ E.coli across species 43 . Finally, we also searched for evidence of APOBEC signatures (SBS2/13), which have been reported in a small number of human crypts and are believed to be caused by APOBEC DNA-editing cytidine deaminases.…”

Gut Microbiota as Potential Biomarker and/or Therapeutic Target to Improve the Management of Cancer: Focus on Colibactin-Producing Escherichia coli in Colorectal Cancer

“…Recently, impact of prebiotics (inulin and galacto-saccharide) on the genotoxicity of CoPEC, was studied in vitro. Unexpected results were obtained with an increase of DNA damage induced by the CoPEC after the treatment [ 148 ]. Preclinical studies are needed to confirm these data.…”

Shining a Light on Colibactin Biology

“…Spermidine, a polyamine produced during bacterial metabolism or scavenged from the environment is necessary for the production of colibactin [ 14 ]. Administration of oligosaccharide prebiotics, such as inulin or glucose, similarly enhance clbA transcription and pks + genotoxicity [ 37 ]. In contrast, metabolites promoting pks transcription can be attenuated by inhibitory factors (such as ferrous sulfate [ 37 ]), suggesting that regulation of colibactin production is thus intrinsically linked to metabolic conditions within the intestinal lumen or the mucosal lining.…”

“…Administration of oligosaccharide prebiotics, such as inulin or glucose, similarly enhance clbA transcription and pks + genotoxicity [ 37 ]. In contrast, metabolites promoting pks transcription can be attenuated by inhibitory factors (such as ferrous sulfate [ 37 ]), suggesting that regulation of colibactin production is thus intrinsically linked to metabolic conditions within the intestinal lumen or the mucosal lining. These findings are particularly relevant when considering how the carcinogenic activity of pks + E. coli may be enhanced in colitis or CRC patients, who often present with anemia [ 38 ] or other disruptions to metabolic homeostasis which may alter pks transcription.…”