Reevaluation of whether a Functional Agr-like Quorum-Sensing System Is Necessary for Production of Wild-Type Levels of Epsilon-Toxin by Clostridium perfringens Type D Strains

Clostridium perfringens type B and D strains produce epsilon-toxin (ETX). Our 2011 mBio study (mBio 2:e00275-11, 2011, https://doi.org/10.1128/mBio.00275-11) reported that the Agr quorum-sensing (QS) system regulates ETX production by type D strain CN3718. However, subsequent studies have brought that conclusion into question. For example, we reported in 2012 (Infect Immun 80:3008–3017, 2012, https://doi.org/10.1128/IAI.00438-12) that the Agr-like QS system is not required for wild-type ETX production levels by two type B strains. Consequently, we reexamined whether the Agr-like QS system regulates ETX production in type D strains by using Targetron insertional mutagenesis to construct new agrB null mutants of two type D strains, CN3718 and CN2068. Western blotting showed that both agrB mutants still produce wild-type ETX levels. However, the newly constructed agrB mutants of both type D strains produced reduced amounts of alpha-toxin, and this effect was reversible by complementation, which confirms loss of functional AgrB production by these mutants since alpha-toxin production is known to be regulated by AgrB. Coupled with the previously published results for type B strains, these new findings indicate the Agr-like QS system is not usually necessary for C. perfringens to produce wild-type ETX levels.