title: The Borrelia burgdorferi RelA/SpoT Homolog and Stringent Response Regulate Survival in the Tick Vector and Global Gene Expression during Starvation.
abstract: As the Lyme disease bacterium Borrelia burgdorferi traverses its enzootic cycle, alternating between a tick vector and a vertebrate host, the spirochete must adapt and persist in the tick midgut under prolonged nutrient stress between blood meals. In this study, we examined the role of the stringent response in tick persistence and in regulation of gene expression during nutrient limitation. Nutritionally starving B. burgdorferi in vitro increased the levels of guanosine tetraphosphate (ppGpp) and guanosine pentaphosphate (pppGpp), collectively referred to as (p)ppGpp, products of the bifunctional synthetase/hydrolase RelBbu (RelA/SpoT homolog). Conversely, returning B. burgdorferi to a nutrient-rich medium decreased (p)ppGpp levels. B. burgdorferi survival in ticks between the larval and nymph blood meals, and during starvation in vitro, was dependent on RelBbu. Furthermore, normal morphological conversion from a flat-wave shape to a condensed round body (RB) form during starvation was dependent on RelBbu; relBbu mutants more frequently formed RBs, but their membranes were compromised. By differential RNA sequencing analyses, we found that RelBbu regulates an extensive transcriptome, both dependent and independent of nutrient stress. The RelBbu regulon includes the glp operon, which is important for glycerol utilization and persistence in the tick, virulence factors and the late phage operon of the 32-kb circular plasmid (cp32) family. In summary, our data suggest that RelBbu globally modulates transcription in response to nutrient stress by increasing (p)ppGpp levels to facilitate B. burgdorferi persistence in the tick.
authors.affiliation: Division of Biological Sciences, University of Montana, Missoula, Montana, United States of America.
authors.forename: Dan
authors.initials: D
authors.lastname: Drecktrah
authors.affiliation: Department of Biology, University of Colorado, Colorado Springs, Colorado, United States of America; Department of Biochemistry and Cell Biology, Max F. Perutz Laboratories, University of Vienna, Vienna, Austria.
authors.forename: Meghan
authors.initials: M
authors.lastname: Lybecker
authors.affiliation: Oxford NIHR Biomedical Research Centre, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, United Kingdom; Center for Integrative Bioinformatics Vienna, Max F. Perutz Laboratories, University of Vienna & Medical University of Vienna, Vienna, Austria.
authors.forename: Niko
authors.initials: N
authors.lastname: Popitsch
authors.affiliation: Center for Integrative Bioinformatics Vienna, Max F. Perutz Laboratories, University of Vienna & Medical University of Vienna, Vienna, Austria.
authors.forename: Philipp
authors.initials: P
authors.lastname: Rescheneder
authors.affiliation: Division of Biological Sciences, University of Montana, Missoula, Montana, United States of America.
authors.forename: Laura S
authors.initials: LS
authors.lastname: Hall
authors.affiliation: Division of Biological Sciences, University of Montana, Missoula, Montana, United States of America; Center for Biomolecular Structure and Dynamics, University of Montana, Missoula, Montana, United States of America.
authors.forename: D Scott
authors.initials: DS
authors.lastname: Samuels
mesh_terms: D000818:Animals; D001096:Arachnid Vectors / Q000382:microbiology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D025065:Borrelia burgdorferi / Q000235:genetics / Q000254:growth & development / Q000502:physiology* / Q000648:ultrastructure; D041981:Gastrointestinal Tract / Q000382:microbiology; D015964:Gene Expression Regulation, Bacterial; D006158:Guanosine Pentaphosphate / Q000378:metabolism; D006159:Guanosine Tetraphosphate / Q000378:metabolism; D018884:Ixodes / Q000382:microbiology* / Q000502:physiology; D007814:Larva / Q000382:microbiology / Q000502:physiology; D050296:Microbial Viability; D008855:Microscopy, Electron, Scanning; D009154:Mutation; D009758:Nymph / Q000382:microbiology / Q000502:physiology; D009876:Operon; D011755:Pyrophosphatases / Q000235:genetics / Q000378:metabolism*; D018085:Regulon; D013312:Stress, Physiological; D051996:Transcription Factor RelA / Q000235:genetics / Q000378:metabolism; D059467:Transcriptome
chemical_list: D001426:Bacterial Proteins; D051996:Transcription Factor RelA; D006159:Guanosine Tetraphosphate; D006158:Guanosine Pentaphosphate; C027627:guanosine-3',5'-bis(diphosphate) 3'-pyrophosphatase; D011755:Pyrophosphatases