PROJECT SUMMARY The Gram-positive Actinobacteria, including the oral colonizers Actinomyces oris and Corynebacterium matruchotii, as well as the diphtheria-causing pathogen Corynebacterium diphtheriae, employ a disulfide-bond forming machine, MdbA, to promote oxidative protein folding. In A. oris and C. diphtheriae, MdbA catalyzes disulfide bond formation in pilin substrates that are required for oral biofilm formation and polymicrobial interactions. This diversity supplement supports the research training of a graduate student who aims to characterize a conserved membrane protein – working in conjunction with MdbA – that maintains membrane-homoeostasis of an enzyme essential for formation of oral biofilms and polymicrobial interactions. The results generated will advance our understanding of assembly and folding of factors contributing to the development of oral biofilms.