Cyclic di-gmp is essential for the survival of the lyme disease spirochete in ticks

Cyclic dimeric gmp (c-di-gmp) is a bacterial second messenger that modulates many biological processes. although its role in bacterial pathogenesis during mammalian infection has been documented,the role of c-di-gmp in a pathogen's life cycle within a vector host is less understood. the enzootic cycle of the lyme disease pathogen borrelia burgdorferi involves both a mammalian host and an ixodes tick vector. the b. burgdorferi genome encodes a single copy of the diguanylate cyclase gene (rrp1),which is responsible for c-di-gmp synthesis. to determine the role of c-di-gmp in the life cycle of b. burgdorferi,an rrp1-deficient b. burgdorferi strain was generated. the rrp1 mutant remains infectious in the mammalian host but cannot survive in the tick vector. microarray analyses revealed that expression of a four-gene operon involved in glycerol transport and metabolism,bb0240-bb0243,was significantly downregulated by abrogation of rrp1. in vitro,the rrp1 mutant is impaired in growth in the media containing glycerol as the carbon source (bsk-glycerol). to determine the contribution of the glycerol metabolic pathway to the rrp1 mutant phenotype,a glp mutant,in which the entire bb0240-bb0243 operon is not expressed,was generated. similar to the rrp1 mutant,the glp mutant has a growth defect in bsk-glycerol medium. in vivo,the glp mutant is also infectious in mice but has reduced survival in ticks. constitutive expression of the bb0240-bb0243 operon in the rrp1 mutant fully rescues the growth defect in bsk-glycerol medium and partially restores survival of the rrp1 mutant in ticks. thus,c-di-gmp appears to govern a catabolic switch in b. burgdorferi and plays a vital role in the tick part of the spirochetal enzootic cycle. this work provides the first evidence that c-di-gmp is essential for a pathogen's survival in its vector host.