Environmental Control of Queuosine Levels in <i>Streptococcus mutans</i><scp>tRNAs</scp>

Queuosine (Q) is a modification of the wobble base in tRNAs that decode NA(C/U) codons. It is ubiquitous in bacteria, including many pathogens. Streptococcus mutans is an early colonizer of dental plaque biofilm and a key player in dental caries. Using a combination of genetic and physiological approaches, the predicted Q synthesis and salvage pathways were validated in this organism. These experiments confirmed that S. mutans can synthesize Q de novo through similar pathways found in Bacillus subtilis and Escherichia coli. However, S. mutans has a distinct salvage pathway compared to these model organisms, as it uses a transporter belonging to the energy coupling factor (ECF) family controlled by a preQ₁-dependent riboswitch. Furthermore, Q levels in this oral pathogen depended heavily on the media composition, suggesting that micronutrients can affect Q-mediated translation efficiency.