Competitive and cooperative interactions between organisms, including bacteria, can significantly impact the composition of a community and the fitness of its members, as well as the fitness of their hosts when communities are living on or within other organisms. Understanding the underlying mechanisms is critical to the development of strategies to control microbiological communities that impact animal and plant health and also for understanding the evolution of social behaviors, which has been challenging for evolutionary biologists. Contact-dependent growth inhibition (CDI) is a phenomenon defined by the delivery of a protein toxin to the cytoplasm of neighboring bacteria upon cell–cell contact, resulting in growth inhibition or death unless a specific immunity protein is present. CDI was first described based on observations of interbacterial killing and has been assumed to function primarily as a means of eliminating competitor cells. However, recent molecular evidence indicates that multiple levels of specificity restrict CDI toxin delivery and activity to the same bacterial strain, and that CDI system proteins can mediate cooperative behaviors among ‘self’ cells, a phenomenon called contact-dependent signaling (CDS). Here we review these recent findings and discuss potential biological and evolutionary implications of CDI system-mediated interbacterial competition and cooperation.
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Research by the authors’ relating to work described in this review was supported by the National Institutes of Health (R21 AI112764 and R01 GM121110 to P.A.C.; F32 AI096728 and K22 AI118949 to E.C.G.; E.S.D. was supported by K12GM00678 from the Training, Workforce Development, and Diversity division of the NIGMS).
Danka, Elizabeth S.; Garcia, Erin C.; and Cotter, Peggy A., "Are CDI Systems Multicolored, Facultative, Helping Greenbeards?" (2017). Microbiology, Immunology, and Molecular Genetics Faculty Publications. 138.