RT Journal Article SR Electronic T1 Microniches in biofilm depth are hot-spots for antibiotic resistance acquisition in response to in situ stress JF bioRxiv FD Cold Spring Harbor Laboratory SP 2021.11.03.467100 DO 10.1101/2021.11.03.467100 A1 Linda Tlili A1 Marie-Cécile Ploy A1 Sandra Da Re YR 2021 UL http://biorxiv.org/content/early/2021/11/03/2021.11.03.467100.abstract AB Class 1 integrons play a major role in antibiotic resistance dissemination among Gram-negative bacteria. They are genetic platforms able to capture, exchange and express antibiotic resistance gene cassettes. The integron integrase, whose expression is regulated by the bacterial SOS response, is the key element of the integron catalyzing insertion/excision/shuffling of gene cassettes. We previously demonstrated that the basal level of integrase expression and in consequence, its activity, is increased via the starvation-induced stringent response in the biofilm population. However, biofilms are heterogeneous environments where bacteria are under various physiological states. Here we thus analyzed at the bacterial level, the SOS response and integrase expression within the biofilm, using confocal microscopy and flow cytometry. We showed that in the absence of exogenous stress, only a small number of bacteria (~ 1%) located in the depth of the biofilm induce the SOS-response leading to a high level of integrase expression, through both a stringent response-dependent and -independent manner. Our results thus indicate that few bacteria located in microniches of the biofilm depth undergo sufficient endogenous stress to promote the acquisition of antibiotic resistance, forming a reservoir of bacteria ready to rapidly resist antibiotic treatments.Competing Interest StatementThe authors have declared no competing interest.