Systematic Analysis of Escherichia coli Isolates from Sheep and Cattle Suggests Adaption to the Rumen Niche

Abstract

The commonly used laboratory bacterium Escherichia coli normally does not produce and secrete cellulases due to its complex bilayer membrane structure and poor secretory apparatus. In our previous study, the cellulolytic E. coli strain ZH-4 with extracellular cellulase activity was found in the bovine rumen. In this study, we demonstrate that the secretion of cellulase is a common feature of E. coli isolated from the rumen, such as sheep and cattle. Physiological phenotype characterization of these E. coli isolates together with genome, transcriptome and comparative genomics analysis suggested their adaption to the rumen niche. The faster growth rate of the isolated strains under aerobic conditions meets the competitive requirements of the strains in rumen microecosystem, while anaerobic accumulation of reduced H2 and succinate was hypothesized to be the results of adaptation to the rumen environment. The cellulase secretion increased significantly when the molecular chaperone genes ibpA and ibpB was overexpressed. These were also revealed by the transcriptomic data. A possible reason of cellulase secretion by E. coli isolates was proposed based on the transcriptomic data and molecular experiments. Importance As an important intestinal microorganism, E. coli is present in the intestinal tract of animals and many other environments. However, it normally does not produce and secret cellulases due to its complex bilayer membrane structure and poor secretory apparatus. Here, we proved that E. coli is widely present in the rumen of sheep and cattle. Systematic analysis of the isolates indicated that they have adapted to the rumen niche, with phenotypes including secretion of cellulase and fermentative accumulation of succinate and H2. The finding that overexpression small heat shock protein genes ibpA and ibpB could facilitate cellulase BcsZ secretion, which provides a possible insight into the protein secretion mechanism of rumen colonizing E. coli.

Prevalence of Antibiotic Resistance and Virulence Genes in Escherichia coli Carried by Migratory Birds on the Inner Mongolia Plateau of Northern China from 2018 to 2023

“…They were densely distributed on the evolutionary tree, mostly in later evolutionary branches. Some sequence type isolates (ST48, ST155, ST602 and ST906) were closely related to human or domestic animal isolates [ 55 , 56 ]. This further proves the close relationship between human activities and epidemic strains of wildlife.…”