Transcriptome analysis of enterotoxigenic escherichia coli (ETEC) isolates exposed to cabbage

Abstract

Enterotoxigenic Escherichia coli (ETEC) is a food-borne pathogen causing diarrhea among children in developing countries as well as travelers in ETEC endemic areas. Recent studies have revealed that many outbreaks of ETEC were mediated by fresh produce such as sprouts or lettuce. To understand how ETEC adapt to fresh produce, ETEC FORC31 isolated from stool of a patient suffered from foodborne disease in Korea was cultivated in the presence of cabbage (Brassica oleracea var. capitata L.). Planktonic cells exposed to cabbage were subjected to RNA sequencing to obtain bacterial gene expression profiles. As a result, among a total of 5,391 annotated coding DNA sequences, 1.13% and 0.74% of total genes were significantly up- or down-regulated when contacted with cabbage for 4 h. Differently expressed genes (p-value ≤ 0.05, fold-change ≥ 5) were grouped mainly into five categories according to COG designations: amino acid transport/metabolism, nucleotide transport/metabolism, cell motility, inorganic ion transport/metabolism, and signal transduction mechanisms. This indicates that ETEC FORC31 may utilize various nutritional factors released from cabbage to promote its growth and survival. Particularly, RNA-Seq revealed that molybdenum-related genes including molybdate transporter and molybdenum cofactor (Moco) biosynthesis operons are differentially expressed when the bacteria were exposed to cabbage. Molybdate used for Moco biosynthesis, and Moco is found in a number of different molybdoenzymes, which involve carbon, sulfur, and nitrogen metabolisms. It was further demonstrated that ETEC FORC31 ΔmoeAB defective in Moco biosynthesis had reduced motility and changed curli production in the presence of excess nitrate. In addition, ΔmoeAB was more sensitive to organic acid than wild type. These results indicate that molybdenum metabolism significantly affects for survival of ETEC in cabbage. Therefore, to reduce ETEC contamination in cabbage, organic acid treatment is carefully conducted because up-regulated Moco biosynthesis genes may affect bacterial acid resistance.