BB0562 is a nutritional virulence determinant with lipase activity important for Borrelia burgdorferi infection and survival in fatty acid deficient environments

The Lyme disease spirochete Borrelia burgdorferi relies on uptake of essential nutrients from its host environments for survival and infection. Therefore, nutrient acquisition mechanisms constitute key virulence properties of the pathogen, yet these mechanisms remain largely unknown. In vivo expression technology applied to B. burgdorferi (BbIVET) during mammalian infection identified gene bb0562, which encodes a hypothetical protein comprised of a conserved domain of unknown function, DUF3996. DUF3996 is also found across adjacent encoded hypothetical proteins BB0563 and BB0564, suggesting the possibility that the three proteins could be functionally related. Deletion of bb0562, bb0563 and bb0564 individually and together demonstrated that bb0562 alone was important for optimal disseminated infection in immunocompetent and immunocompromised mice by needle inoculation and tick bite transmission. Moreover, bb0562 promoted spirochete survival during the blood dissemination phase of infection. Gene bb0562 was also found to be important for spirochete growth in low serum media and the growth defect of Δbb0562 B. burgdorferi was rescued with the addition of various long chain fatty acids, particularly oleic acid. In mammals, fatty acids are primarily stored in fat droplets in the form of triglycerides. Strikingly, addition of glyceryl trioleate, the triglyceride form of oleic acid, to the low serum media did not rescue the growth defect of the mutant, suggesting bb0562 may be important for the release of fatty acids from triglycerides. Therefore, we searched for and identified two canonical GXSXG lipase motifs within BB0562, despite the lack of homology to known bacterial lipases. Purified BB0562 demonstrated lipolytic activity dependent on the catalytic serine residues within the two motifs. In sum, we have established that bb0562 is a novel nutritional virulence determinant, encoding a lipase that contributes to fatty acid scavenge for spirochete survival in environments deficient in free fatty acids including the mammalian host.

Borrelia burgdorferi, the causative agent of Lyme disease, has a small genome and lacks the ability to synthesize essential nutrients on its own as well as many of the virulence properties typical of bacterial pathogens that contribute to disease. The clinical manifestations of Lyme disease predominantly result from inflammation in response to the B. burgdorferi infection. Therefore, nutrient acquisition functions constitute key virulence factors for the pathogen. Fatty acids are critical components of B. burgdorferi membranes and lipoproteins, which the spirochete must scavenge from the host environment. Previously, through a genetic screen for B. burgdorferi genes that are expressed during mammalian infection we identified gene of unknown function, bb0562. Herein, we demonstrate that bb0562 encodes a lipase that plays a role in the release of free fatty acids from triglycerides. Furthermore, bb0562 contributes to B. burgdorferi survival and dissemination in the mammalian host. BB0562 is important for spirochete survival in environments low in free fatty acids thereby adding to B. burgdorferi’s arsenal of nutritional virulence determinants necessary for the pathogen to be maintained in the tick-mouse enzootic cycle and to cause disseminated disease.

Evaluation of the Pig-Tailed Macaque (Macaca nemestrina) as a Model of Human Staphylococcus aureus Nasal Carriage

Staphylococcus aureus nasal carriage is a common condition affecting both healthy and immunocompromised populations and provides a reservoir for dissemination of potentially infectious strains by casual contact. The factors regulating the onset and duration of nasal S. aureus colonization are mostly unknown, and a human-relevant animal model is needed. Here, we screened 17 pig-tailed macaques (Macaca nemestrina) for S. aureus carriage, and 14 of 17 animals tested positive in the nose at one or both screening sessions (8 weeks apart), while the other 3 animals were negative in the nose but positive in the pharynx at least once. As in humans, S. aureus colonization was densest in the nose, and treatment of the nostrils with mupirocin ointment effectively cleared the nostrils and 6 extranasal body sites. Experimental nasal S. aureus colonization was established with 104 CFU/nostril, and both autologous and nonautologous strains survived over 40 days without any apparent adverse effects. A human nasal S. aureus isolate (strain D579, sequence type 398) was carried in 4 of 6 animals for over 3 weeks. Nostrils that did eradicate experimentally applied S. aureus exhibited neutrophilic innate immunity marked by elevated nasal interleukin-1β (IL-1β), IL-8, and monocyte chemotactic protein 1 levels and a 10-fold decreased IL-1 receptor antagonist/IL-1β ratio within 7 days postinoculation, analogous to the human condition. Taken together, pig-tailed macaques represent a physiological model of human S. aureus nasal carriage that may be utilized for testing natural colonization and decolonization mechanisms as well as novel classes of anti-S. aureus therapeutics.

Riboflavin salvage by Borrelia burgdorferi supports carbon metabolism and is essential for survival in the tick vector

The Lyme disease agent, Borrelia burgdorferi, harbors a significantly reduced genome and relies on the scavenging of critical nutrients from its tick and mammalian hosts for survival. Riboflavin salvage has been shown to be important for B. burgdorferi infection of mice, yet the contributions of riboflavin to B. burgdorferi metabolism and survival in the tick remain unknown. Using a targeted mass spectrometry approach, we confirmed the importance of bb0318, the putative ATPase component of an ABC-type riboflavin transporter, for riboflavin salvage and the production of FMN and FAD. This analysis further revealed that Δbb0318 B. burgdorferi displayed increased levels of glycerol 3-phosphate compared to the wild-type. The glycerol 3-phosphate dehydrogenase activity of GlpD was found to be FAD-dependent and the transcription and translation of glpD were significantly decreased in Δbb0318 B. burgdorferi. Finally, gene bb0318 was found to be important for maximal spirochete burden in unfed larvae and essential for survival in feeding ticks. Together, these data demonstrate the importance of riboflavin salvage for B. burgdorferi carbon metabolism and survival in ticks.

Broadly conserved FlgV controls flagellar assembly and Borrelia burgdorferi dissemination in mice

Flagella propel pathogens through their environments yet are expensive to synthesize and are immunogenic. Thus, complex hierarchical regulatory networks control flagellar gene expression. Spirochetes are highly motile bacteria, but peculiarly in the Lyme spirochete Borrelia burgdorferi, the archetypal flagellar regulator σ28 is absent. We rediscovered gene bb0268 in B. burgdorferi as flgV, a broadly-conserved gene in the flagellar superoperon alongside σ28 in many Spirochaetes, Firmicutes and other phyla, with distant homologs in Epsilonproteobacteria. We found that B. burgdorferi FlgV is localized within flagellar motors. B. burgdorferi lacking flgV construct fewer and shorter flagellar filaments and are defective in cell division and motility. During the enzootic cycle, B. burgdorferi lacking flgV survive and replicate in Ixodes ticks but are attenuated for dissemination and infection in mice. Our work defines infection timepoints when spirochete motility is most crucial and implicates FlgV as a broadly distributed structural flagellar component that modulates flagellar assembly.

Evaluation of the pig-tailed macaque (Macaca nemestrina) as a model of human Staphylococcus aureus nasal carriage

Staphylococcus aureus (SA) nasal carriage is a common condition effecting both healthy and immunocompromised populations, and provides a reservoir for dissemination of potentially infectious strains by casual contact. Factors regulating the onset and duration of nasal SA colonization are mostly unknown, and a human-relevant animal model is needed. Here, we screened 17 pig-tailed macaques (Macaca nemestrina) for SA carriage, and 14 of 17 animals tested positive in the nose at one or both screening sessions (8 weeks apart), while the other three animals were negative in the nose but positive in the pharynx at least once. Similar to humans, SA colonization was densest in the nose, and treatment of the nostrils with mupirocin ointment effectively cleared the nostrils and 6 extra-nasal body sites. Experimental nasal SA colonization was established with 104 CFU/nostril, and both autologous and non-autologous strains survived over 40 days without any apparent adverse effects. A human nasal SA isolate (D579/ST398) was carried in 4 of 6 animals for over three weeks. Nostrils that did eradicate experimentally applied SA exhibited neutrophilic innate immunity marked by elevated nasal IL-1β, IL-8, and MCP-1, and a 10-fold decreased IL-1RA:IL-1β ratio within 7 days post-inoculation, analogous to the human condition. Taken together, pig-tailed macaques represent a physiological model of human SA nasal carriage with utility for testing natural colonization and decolonization mechanisms, and novel classes of anti-SA therapeutics.

Broadly conserved FlgV controls flagellar assembly and Borrelia burgdorferi dissemination in mice

Flagella propel pathogens through their environments, yet are expensive to synthesize and are immunogenic. Thus, complex hierarchical regulatory networks control flagellar gene expression. Spirochetes are highly motile bacteria, but peculiarly, the archetypal flagellar regulator σ28 is absent in the Lyme spirochete Borrelia burgdorferi. Here, we show that gene bb0268 (flgV) in B. burgdorferi, previously and incorrectly annotated to encode the RNA-binding protein Hfq, is instead a structural flagellar component that modulates flagellar assembly. The flgV gene is broadly conserved in the flagellar superoperon alongside σ28 in many Spirochaetae, Firmicutes and other phyla, with distant homologs in Epsilonproteobacteria. We find that B. burgdorferi FlgV is localized within flagellar basal bodies, and strains lacking flgV produce fewer and shorter flagellar filaments and are defective in cell division and motility. During the enzootic cycle, flgV-deficient B. burgdorferi survive and replicate in Ixodes ticks but are attenuated for infection and dissemination in mice. Our work defines infection timepoints when spirochete motility is most crucial and implicates FlgV as a broadly distributed structural flagellar component that modulates flagellar assembly.