ABSTRACT: Enterococcus faecalis is a commensal bacterium in the gastrointestinal tract (GIT) of humans and other organisms. Outside of the GIT, E. faecalis can cause infections in root canals, wounds, surgical sites, the urinary tract, and on heart valves. Many of these infections can be polymicrobial, and a variety of toxins and nutritional signals influence interactions between E. faecalis and other microbes. Like other bacteria, E. faecalis metabolizes arginine through the arginine deiminase (ADI) pathway, which converts arginine to ornithine and releases ATP, ammonia, and CO2. E. faecalis arginine metabolism also affects virulence of other pathogens, such as Clostridioides difficile and Escherichia coli, during co-culture. E. faecalis may encounter elevated levels of arginine in the GIT or the oral cavity, where arginine is used as an additive in dental therapeutics to disrupt plaque formation and biofilm growth by oral streptococci. However, little is known about how E. faecalis responds to growth in arginine. To address this gap, we used RNAseq and additional in vitro assays to measure changes in growth, gene expression, and biofilm formation in arginine relative to control conditions. Here, we demonstrate that arginine decreases E. faecalis biofilm production and causes widespread differential expression of genes related to metabolism, nutrient transport, quorum sensing, and polysaccharide synthesis. Growth in arginine also increases aggregation of E. faecalis cultures and promotes decreased susceptibility to the antibiotics ampicillin and ceftriaxone. Together, this shows that E. faecalis undergoes global transcriptional changes during growth in arginine and provides a platform for better understanding of how the presence of arginine in the niches colonized by E. faecalis affects the physiology of this organism in addition to the virulence of surrounding microbes.
