The LuxS-Dependent Quorum-Sensing System Regulates Early Biofilm Formation by Streptococcus pneumoniae Strain D39

<jats:title>ABSTRACT</jats:title> <jats:p> <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Streptococcus pneumoniae</jats:named-content> is the leading cause of death in children worldwide and forms highly organized biofilms in the nasopharynx, lungs, and middle ear mucosa. The <jats:italic>luxS</jats:italic> -controlled quorum-sensing (QS) system has recently been implicated in virulence and persistence in the nasopharynx, but its role in biofilms has not been studied. Here we show that this QS system plays a major role in the control of <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">S. pneumoniae</jats:named-content> biofilm formation. Our results demonstrate that the <jats:italic>luxS</jats:italic> gene is contained by invasive isolates and normal-flora strains in a region that contains genes involved in division and cell wall biosynthesis. The <jats:italic>luxS</jats:italic> gene was maximally transcribed, as a monocistronic message, in the early mid-log phase of growth, and this coincides with the appearance of early biofilms. Demonstrating the role of the LuxS system in regulating <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">S. pneumoniae</jats:named-content> biofilms, at 24 h postinoculation, two different D39Δ <jats:italic>luxS</jats:italic> mutants produced ∼80% less biofilm biomass than wild-type (WT) strain D39 did. Complementation of these strains with <jats:italic>luxS</jats:italic> , either in a plasmid or integrated as a single copy in the genome, restored their biofilm level to that of the WT. Moreover, a soluble factor secreted by WT strain D39 or purified AI-2 restored the biofilm phenotype of D39Δ <jats:italic>luxS</jats:italic> . Our results also demonstrate that during the early mid-log phase of growth, LuxS regulates the transcript levels of <jats:italic>lytA</jats:italic> , which encodes an autolysin previously implicated in biofilms, and also the transcript levels of <jats:italic>ply</jats:italic> , which encodes the pneumococcal pneumolysin. In conclusion, the <jats:italic>luxS</jats:italic> -controlled QS system is a key regulator of early biofilm formation by <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">S. pneumoniae</jats:named-content> strain D39. </jats:p>