An energy coupling factor transporter of Streptococcus sanguinis impacts antibiotic susceptibility as well as metal and membrane homeostasis

Streptococcus sanguinis is a prevalent member of human microbiome capable of acting as a causative agent of oral and respiratory infections. S. sanguinis competitive success within the infection niche is dependent on acquisition of metal ions and vitamins. Among the systems that bacteria use for micronutrient uptake is the energy coupling factor (ECF) transporter system EcfAAT. Here we describe physiological changes arising from EcfAAT transporter disruption. We found that EcfAAT contributes to S. sanguinis antibiotic sensitivity as well as metal and membrane homeostasis. Specifically, our work found that disruption of EcfAAT results in increased polymyxin susceptibility. We performed assessment of cell-associated metal content and found depletion of iron, magnesium, and manganese. Furthermore, membrane composition analysis revealed significant enrichment in unsaturated fatty acid species resulting in increased membrane fluidity. Our results demonstrate how disruption of a single EcfAAT transporter can have broad consequences on bacterial cell homeostasis. ECF transporters are of interest within the context of infection biology in bacterial species other than streptococci, hence work described here will further the understanding of how micronutrient uptake systems contribute to bacterial pathogenesis. ImportanceProficiency in micronutrient uptake is key for pathogen success in bacteria-bacteria and bacteria-host interactions within the infection context. Micronutrient uptake mechanisms are of interest in furthering the understanding of bacterial physiology within infection niche and as targets for design of antimicrobials. Here we describe how a deletion of a nutrient uptake transporter in S. sanguinis alters bacterial sensitivity to antibiotics. We also show that a defect in this candidate nutrient uptake system has consequences on the intracellular metal content, and also results in changes in membrane fatty acid composition and fluidity. This study demonstrates how disruption of a single nutrient uptake system disrupts bacterial physiology resulting in increased antibiotic sensitivity.