L-Arabinose alters the E. coli transcriptome to favor biofilm growth and enhances survival with fluoroquinolone stress
Environmental conditions, including nutrient composition and temperature, influence biofilm formation and antibiotic resistance in Escherichia coli. Understanding how specific metabolites modulate these processes is critical for improving antimicrobial strategies. Here, we investigated the growth and composition of Escherichia coli in both planktonic and biofilm states under the influence of L-arabinose, with and without exposure to the fluoroquinolone antibiotic levofloxacin, at two temperatures: 28?°C, optimal for biofilm development, and 37?°C, representative of human physiological conditions. L-arabinose increased the growth rate of planktonic E. coli but resulted in less total planktonic growth overall; L-arabinose addition also enhanced biofilm growth at 37 °C. L-arabinose reduced the efficacy of the fluoroquinolone levofloxacin and promoted growth in sub-minimum inhibitory concentrations of the antibiotic.  We conducted transcriptomic analyses at both temperatures to gain insight into the molecular basis of arabinose-mediated reduced susceptibility of E. coli to levofloxacin. We found that L-arabinose had a temperature- and state-dependent impact on the transcriptome. Using gene ontology overrepresentation analyses, we found that L-arabinose modulated the expression of many critical antibiotic resistance genes, including efflux pumps, transporters, and biofilm-related genes for external structures like pili and curli. This study demonstrates a previously uncharacterized role for L-arabinose in modulating antibiotic resistance and biofilm-associated gene expression in E. coli and provides a foundation for additional exploration of sugar-mediated antibiotic sensitivity in bacterial biofilms. Overall design: PHL628 E. coli cells were grown in rich (LB) media supplemented with either L-arabinose at 0.5% (w/w) or no sugar (0%, LB samples).  Cells were grown at either 28 °C or 37 °C and three biological replicates of planktonic and biofilm samples of each experimental condition type were harvested (8 conditions, 24 samples total).