The experimental laboratory work was divided into three work packages (WP):
WP1. - “Impact of drug-induced evolution on microbiome antibiotic sensitivity and metabolism”
To investigate the extent and potential of gut microbial evolution upon the exposure of individual bacterial strains to non-antibiotic compounds, we performed a pilot in vitro evolution experiment with four representative gut bacterial strains in the presence of ten drugs that can act as cellular stressors. Throughout the drug exposure, we monitored changes in microbial drug resistance. The selection of the drugs and bacterial species was based on an extensive analysis from the existing literature and new experimental data generated for this project. Our results demonstrated that long exposure to subinhibitory concentration of non-antibiotic drugs can induce drug resistance in a diverse gut bacterial species. Additionally, we collected data of the in vitro growth parameters of ten representative human gut bacteria and determined the minimal inhibitory concentration of approximately 160 drug-bacteria combinations. The methods and the results established in this WP can be used for current and future projects on the topic in the hosting lab.
WP2- “Role of the SOS and RpoS response in microbiome evolution”
Based on previous studies on the gut bacteria sensitivity to human-targeted drugs, we hypothesized that these non-antibiotic drugs, similar to antibiotics, could act as stressors and activate two stress transcriptional programs named the SOS and RpoS responses. Both pathways can cause mutagenesis in bacterial genomes and they have been associated with microbial evolution acceleration and its consequences in the antimicrobial resistance development in bacterial pathogens. However, there is currently no understanding how these transcriptional programs function in gut bacteria, in particular in the most abundant and prevalent human commensal of Bacteroides spp. To gain insights in these molecular mechanisms, we studied the role of LexA and RpoS homologues (the stress responses regulators, respectively) in Bacteroides thetaiotaomicron as a model. Using molecular microbiology, culturomics and transcriptomics, we found that LexA may play a different role in this species. We are currently analyzing the transcriptomics data of the rpoS mutant in B. thetaiotaomicron. Furthermore, we developed various molecular biology tools for the Bacteroides spp. research, such as the mutagenesis system and the luminescent reporters, that are available to be used for current and future studies in these species.
WP 3. “Drug-induced microbiome evolution in vivo using gnotobiotic mouse models”
In this WP, we validated the in vitro results in vivo using a gnotobiotic mouse model. Briefly, we performed a competition assay of different B. thetaiotaomicron lexA mutants strains to gain insight into their role in mouse gut colonization. For strain identification, we used the newly barcoding method followed by sequencing. Currently the data is under processing.
The results of the three WPs were presented to the scientific community on various occasions including international conferences and seminars. Together the data is currently being written up for peer- review in an OA journal to be submitted in October 2024.