Quorum sensing (QS) is a well-known chemical signaling system responsible for intercellular communication that is widespread in bacteria.
Acyl-homoserine lactone (AHL) is the most-studied QS signal. Previously, bacterially encoded AHL-degrading
enzymes were considered to be canonical quorum-quenching
proteins that have been widely used to control pathogenic
infections. Here, we report a novel platform that enabled the efficient discovery of noncanonical AHL quorum-quenching
proteins. This platform initially asked bacteriologists to carry out comparative genomic analyses between phylogenetically related AHL-producing and non-AHL-producing members to identify genes that are conservatively shared by non-AHL-producing members but absent in AHL-producing species. These candidate genes were then introduced into recombinant AHL-producing E. coli to screen for target
proteins with the ability to block AHL production. Via this platform, we found that non-AHL-producing Lysobacter containing numerous environmentally ubiquitous members encoded a conserved
glycosyltransferase-like
protein Le4759, which was experimentally shown to be a noncanonical AHL-quenching
protein. Le4759 could not directly degrade exogenous AHL but rather recognized and altered the activities of multiple AHL synthases through
protein-
protein interactions. This versatile capability enabled Le4759 to block specific
AHL synthase such as CarI from Pectobacterium carotovorum to reduce its
protein abundance to suppress AHL synthesis, thereby impairing
bacterial infection. Thus, this study provided bacteriologists with a unique platform to discover noncanonical quorum-quenching
proteins that could be developed as promising next-generation
drug candidates to overcome emerging bacterial antibiotic resistance. IMPORTANCE Targeting and blocking bacterial quorum sensing (QS), the process known as quorum quenching (QQ) is an effective mean to control
bacterial infection and overcome the emerging antibiotic resistance. Previously, diverse QS signal-degradation
enzymes are identified as canonical QQ
proteins. Here, we provided a novel and universal platform that enabled to discover previously unidentified noncanonical QQ
proteins that were unable to degrade
acyl-homoserine lactone (AHL) but could block AHL generation by recognizing multiple AHL synthases via direct
protein-
protein interactions. Our findings are believed to trigger broad interest for bacteriologists to identify potentially widely distributed noncanonical QQ
proteins that have great potential for developing next-generation anti-infectious drugs.