title: Cyclic di-GMP modulates gene expression in Lyme disease spirochetes at the tick-mammal interface to promote spirochete survival during the blood meal and tick-to-mammal transmission.
abstract: Borrelia burgdorferi, the Lyme disease spirochete, couples environmental sensing and gene regulation primarily via the Hk1/Rrp1 two-component system (TCS) and Rrp2/RpoN/RpoS pathways. Beginning with acquisition, we reevaluated the contribution of these pathways to spirochete survival and gene regulation throughout the enzootic cycle. Live imaging of B. burgdorferi caught in the act of being acquired revealed that the absence of RpoS and the consequent derepression of tick-phase genes impart a Stay signal required for midgut colonization. In addition to the behavioral changes brought on by the RpoS-off state, acquisition requires activation of cyclic di-GMP (c-di-GMP) synthesis by the Hk1/Rrp1 TCS; B. burgdorferi lacking either component is destroyed during the blood meal. Prior studies attributed this dramatic phenotype to a metabolic lesion stemming from reduced glycerol uptake and utilization. In a head-to-head comparison, however, the B. burgdorferi Δglp mutant had a markedly greater capacity to survive tick feeding than B. burgdorferi Δhk1 or Δrrp1 mutants, establishing unequivocally that glycerol metabolism is only one component of the protection afforded by c-di-GMP. Data presented herein suggest that the protective response mediated by c-di-GMP is multifactorial, involving chemotactic responses, utilization of alternate substrates for energy generation and intermediary metabolism, and remodeling of the cell envelope as a means of defending spirochetes against threats engendered during the blood meal. Expression profiling of c-di-GMP-regulated genes through the enzootic cycle supports our contention that the Hk1/Rrp1 TCS functions primarily, if not exclusively, in ticks. These data also raise the possibility that c-di-GMP enhances the expression of a subset of RpoS-dependent genes during nymphal transmission.
authors.affiliation: Department of Medicine, University of Connecticut Health Center, Farmington, Connecticut, USA Department of Pediatrics, University of Connecticut Health Center, Farmington, Connecticut, USA Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, Connecticut, USA mcaima@uchc.edu.
authors.forename: Melissa J
authors.initials: MJ
authors.lastname: Caimano
authors.affiliation: Department of Medicine, University of Connecticut Health Center, Farmington, Connecticut, USA.
authors.forename: Star
authors.initials: S
authors.lastname: Dunham-Ems
authors.affiliation: Department of Medicine, University of Connecticut Health Center, Farmington, Connecticut, USA.
authors.forename: Anna M
authors.initials: AM
authors.lastname: Allard
authors.affiliation: Department of Biochemistry and Center for Drug Discovery, Virginia Tech, Blacksburg, Virginia, USA.
authors.forename: Maria B
authors.initials: MB
authors.lastname: Cassera
authors.affiliation: Department of Microbiology and Immunology, University of Oklahoma College of Medicine, Oklahoma City, Oklahoma, USA.
authors.forename: Melisha
authors.initials: M
authors.lastname: Kenedy
authors.affiliation: Department of Medicine, University of Connecticut Health Center, Farmington, Connecticut, USA Department of Pediatrics, University of Connecticut Health Center, Farmington, Connecticut, USA Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, Connecticut, USA Department of Genetics and Genomic Sciences, University of Connecticut Health Center, Farmington, Connecticut, USA Department of Immunology, University of Connecticut Health Center, Farmington, Connecticut, USA.
authors.forename: Justin D
authors.initials: JD
authors.lastname: Radolf
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D025065:Borrelia burgdorferi / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000378:metabolism; D005260:Female; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D008193:Lyme Disease / Q000382:microbiology* / Q000635:transmission; D051379:Mice; D008809:Mice, Inbred C3H; D050296:Microbial Viability; D051381:Rats; D017207:Rats, Sprague-Dawley; D013987:Ticks / Q000382:microbiology* / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; C062025:bis(3',5')-cyclic diguanylic acid; D006152:Cyclic GMP