BrnQ Branched-Chain Amino Acid Transporters Influence Toxin Production by, but Not Growth of, Clostridium perfringens Type A Strain ATCC3624

By producing alpha toxin (PLC) and perfringolysin O (PFO), <i>Clostridium perfringens</i> type A strains are the most common cause of traumatic gas gangrene. <i>C. perfringens</i> cannot synthesize branched-chain amino acids (BCAAs), so BCAA transporters are essential for <i>C. perfringens</i> growth and survival. <i>C. perfringens</i> type A strain ATCC3624 encodes the BrnQ1, BrnQ2, and BrnQ3 BCAA transporters. RT-PCR analyses showed that, with increasing culture time in TY broth, <i>brnQ2</i> and <i>brnQ3</i> expression levels remained stable but <i>brnQ1</i> expression levels declined. Single null mutants unable to produce one of the BrnQ proteins grew and survived similarly as wild type. However, these mutants all showed altered PLC production, especially in the early culture stage, and those effects were reversible by complementation. Therefore, the presence of BrnQ proteins impacts toxin production levels, even though they are not necessary for growth. Interestingly, a triple mutant that was unable to produce any BrnQ protein also grew similarly as ATCC3624. Since BCAA uptake is essential for <i>C. perfringens</i>, this strain must produce another (still to be identified) BCAA transporter.