Spatially localized expression of glutamate decarboxylasegadBinEscherichia coliO157:H7 microcolonies in hydrogel matrix

Abstract

AbstractFunctional diversity within isogenic spatially organized bacterial populations has been shown to trigger emergent community properties such as stress tolerance. Taking advantage of confocal laser scanning microscopy combined with a transcriptional fluorescent fusion reporting at single cell scale the expression of the glutamic acid decarboxylasegadBinE. coliO157:H7, it was possible to visualize for the first-time spatial patterns of bacterial gene expression in microcolonies grown in a gelled matrix. ThegadBgene is involved inE. colitolerance to acidic conditions and its strong over-expression was observed locally on the periphery of embedded microcolonies grown in acidic hydrogels. This spatialization ofgadBexpression did not correlate with live/dead populations that appeared randomly distributed in the colonies. While the planktonic population of the pathogens was eradicated by an exposition to a pH of 2 (HCl) for 4h, mimicking a stomachal acidic stress, bacteria grown in gel-microcolonies were poorly affected by this treatment, in particular in conditions wheregadBwas spatially overexpressed. Consequences of these results for food safety are further discussed.