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.

Correction: The arginine deaminase system plays distinct roles in Borrelia burgdorferi and Borrelia hermsii.

[This corrects the article DOI: 10.1371/journal.ppat.1010370.].

The arginine deaminase system plays distinct roles in Borrelia burgdorferi and Borrelia hermsii.

Borrelia species are amino acid auxotrophs that utilize di- and tri- peptides obtained through their oligopeptide transport system to supply amino acids for replicative growth during their enzootic cycles. However, Borrelia species from both the Lyme disease (LD) and relapsing fever (RF) groups harbor an amino acid transport and catabolism system, the Arginine Deiminase System (ADI), that could potentially augment intracellular L-arginine required for growth. RF spirochetes contain a "complete", four gene ADI (arcA, B, D, and C) while LD spirochetes harbor arcA, B, and sometimes D but lack arcC (encoding carbamate kinase). In this study, we evaluated the role of the ADI system in bacterial survival and virulence and discovered important differences in RF and LD ADIs. Both in vitro and in a murine model of infection, B. hermsii cells significantly reduced extracellular L-arginine levels and that reduction was dependent on arginine deiminase expression. Conversely, B. burgdorferi did not reduce the concentration of L-arginine during in vitro growth experiments nor during infection of the mammalian host, suggesting a fundamental difference in the ability to directly utilize L-arginine compared to B. hermsii. Further experiments using a panel of mutants generated in both B. burgdorferi and B. hermsii, identified important differences in growth characteristics and ADI transcription and protein expression. We also found that the ADI system plays a key role in blood and spleen colonization in RF spirochetes. In this study we have identified divergent metabolic strategies in two closely related human pathogens, that ultimately impacts the host-pathogen interface during infection.

Metabolomic Analysis of Diverse Mice Reveals Hepatic Arginase-1 as Source of Plasma Arginase in Plasmodium chabaudi Infection.

Infections disrupt host metabolism, but the factors that dictate the nature and magnitude of metabolic change are incompletely characterized. To determine how host metabolism changes in relation to disease severity in murine malaria, we performed plasma metabolomics on eight Plasmodium chabaudi-infected mouse strains with diverse disease phenotypes. We identified plasma metabolic biomarkers for both the nature and severity of different malarial pathologies. A subset of metabolic changes, including plasma arginine depletion, match the plasma metabolomes of human malaria patients, suggesting new connections between pathology and metabolism in human malaria. In our malarial mice, liver damage, which releases hepatic arginase-1 (Arg1) into circulation, correlated with plasma arginine depletion. We confirmed that hepatic Arg1 was the primary source of increased plasma arginase activity in our model, which motivates further investigation of liver damage in human malaria patients. More broadly, our approach shows how leveraging phenotypic diversity can identify and validate relationships between metabolism and the pathophysiology of infectious disease. IMPORTANCE Malaria is a severe and sometimes fatal infectious disease endemic to tropical and subtropical regions. Effective vaccines against malaria-causing Plasmodium parasites remain elusive, and malaria treatments often fail to prevent severe disease. Small molecules that target host metabolism have recently emerged as candidates for therapeutics in malaria and other diseases. However, our limited understanding of how metabolites affect pathophysiology limits our ability to develop new metabolite therapies. By providing a rich data set of metabolite-pathology correlations and by validating one of those correlations, our work is an important step toward harnessing metabolism to mitigate disease. Specifically, we showed that liver damage in P. chabaudi-infected mice releases hepatic arginase-1 into circulation, where it may deplete plasma arginine, a candidate malaria therapeutic that mitigates vascular stress. Our data suggest that liver damage may confound efforts to increase levels of arginine in human malaria patients.

DksA-dependent regulation of RpoS contributes to Borrelia burgdorferi tick-borne transmission and mammalian infectivity.

Throughout its enzootic cycle, the Lyme disease spirochete Borreliella (Borrelia) burgdorferi, senses and responds to changes in its environment using a small repertoire of transcription factors that coordinate the expression of genes required for infection of Ixodes ticks and various mammalian hosts. Among these transcription factors, the DnaK suppressor protein (DksA) plays a pivotal role in regulating gene expression in B. burgdorferi during periods of nutrient limitation and is required for mammalian infectivity. In many pathogenic bacteria, the gene regulatory activity of DksA, along with the alarmone guanosine penta- and tetra-phosphate ((p)ppGpp), coordinate the stringent response to various environmental stresses, including nutrient limitation. In this study, we sought to characterize the role of DksA in regulating the transcriptional activity of RNA polymerase and its role in the regulation of RpoS-dependent gene expression required for B. burgdorferi infectivity. Using in vitro transcription assays, we observed recombinant DksA inhibits RpoD-dependent transcription by B. burgdorferi RNA polymerase independent of ppGpp. Additionally, we determined the pH-inducible expression of RpoS-dependent genes relies on DksA, but this relationship is independent of (p)ppGpp produced by Relbbu. Subsequent transcriptomic and western blot assays indicate DksA regulates the expression of BBD18, a protein previously implicated in the post-transcriptional regulation of RpoS. Moreover, we observed DksA was required for infection of mice following intraperitoneal inoculation or for transmission of B. burgdorferi by Ixodes scapularis nymphs. Together, these data suggest DksA plays a central role in coordinating transcriptional responses in B. burgdorferi required for infectivity through DksA's interactions with RNA polymerase and post-transcriptional control of RpoS.

Global Profiling of Lysine Acetylation in Borrelia burgdorferi B31 Reveals Its Role in Central Metabolism.

The post-translational modification of proteins has been shown to be extremely important in prokaryotes. Using a highly sensitive mass spectrometry-based proteomics approach, we have characterized the acetylome of B. burgdorferi. As previously reported for other bacteria, a relatively low number (5%) of the potential genome-encoded proteins of B. burgdorferi were acetylated. Of these, the vast majority were involved in central metabolism and cellular information processing (transcription, translation, etc.). Interestingly, these critical cell functions were targeted during both ML (mid-log) and S (stationary) phases of growth. However, acetylation of target proteins in ML phase was limited to single lysine residues while these same proteins were acetylated at multiple sites during S phase. To determine the acetyl donor in B. burgdorferi, we used mutants that targeted the sole acetate metabolic/anabolic pathway in B. burgdorferi (lipid I synthesis). B. burgdorferi strains B31-A3, B31-A3 ΔackA (acetyl-P- and acetyl-CoA-) and B31-A3 Δpta (acetyl-P+ and acetyl-CoA-) were grown to S phase and the acetylation profiles were analyzed. While only two proteins were acetylated in the ΔackA mutant, 140 proteins were acetylated in the Δpta mutant suggesting that acetyl-P was the primary acetyl donor in B. burgdorferi. Using specific enzymatic assays, we were able to demonstrate that hyperacetylation of proteins in S phase appeared to play a role in decreasing the enzymatic activity of at least two glycolytic proteins. Currently, we hypothesize that acetylation is used to modulate enzyme activities during different stages of growth. This strategy would allow the bacteria to post-translationally stimulate the activity of key glycolytic enzymes by deacetylation rather than expending excessive energy synthesizing new proteins. This would be an appealing, low-energy strategy for a bacterium with limited metabolic capabilities. Future work focuses on identifying potential protein deacetylase(s) to complete our understanding of this important biological process.

Genomic and phenotypic characterization of Borrelia afzelii BO23 and Borrelia garinii CIP 103362.

In recent years, the number of Lyme disease or borreliosis cases in Eurasia has been dramatically increasing. This tick-borne disease is caused by Borrelia burgdorferi sensu lato, which includes B. burgdorferi sensu stricto, the main species found in North America, and B. afzelii and B. garinii, which are primarily responsible for the disease in Eurasia. Currently, research on Lyme disease has focused mainly on B. burgdorferi while B. afzelii and B. garinii, which cause disease with distinctly different symptoms, are less studied. The purpose of this study is to evaluate B. afzelii BO23 and B. garinii CIP 103362 as model organisms to study Eurasian Lyme disease. To begin our analyses, we sequenced, annotated the chromosomes of both species and compared them to B. burgdorferi strain B31. We also assayed shuttle vector, pBSV2, for transformation efficacy and demonstrated that these strains can be cultured on solid media. In addition, we characterized how physicochemical parameters (e.g., oxygen, osmolarity, oxidative stress) affect both growth and motility of the bacteria. Finally, we describe each strain's antibiotic susceptibility and accessed their ability to infect mice. In conclusion, B. afzelii BO23 was more practical for in vitro and in vivo studies than B. garinii CIP 103362.

Borrelia burgdorferi genes, bb0639-0642, encode a putative putrescine/spermidine transport system, PotABCD, that is spermidine specific and essential for cell survival.

Polyamines are an essential class of metabolites found throughout all kingdoms in life. Borrelia burgdorferi harbors no enzymes to synthesize or degrade polyamines yet does contain a polyamine uptake system, potABCD. In this report, we describe the initial characterization of this putative transport system. After several unsuccessful attempts to inactivate potABCD, we placed the operon under the control of an inducible LacI promoter expression system. Analyses of this construct confirmed that potABCD was required for in vitro survival. Additionally, we demonstrated that the potABCD operon were upregulated in vitro by low osmolarity. Previously, we had shown that low osmolarity triggers the activation of the Rrp2/RpoN/RpoS regulatory cascade, which regulates genes essential for the transmission of spirochetes from ticks to mammalian hosts. Interestingly, induction of the pot operon was only affected in an rpoS mutant but not in a rpoN mutant, suggesting that the genes were RpoS dependent and RpoN independent. Furthermore, potABCD was upregulated during tick feeding concomitant with the initiation of spirochete replication. Finally, uptake experiments determined the specificity of B. burgdorferi's PotABCD for spermidine.

Detection of Pathogenic and Non-pathogenic Bacteria in Drinking Water and Associated Biofilms on the Crow Reservation, Montana, USA.

Private residences in rural areas with water systems that are not adequately regulated, monitored, and updated could have drinking water that poses a health risk. To investigate water quality on the Crow Reservation in Montana, water and biofilm samples were collected from 57 public buildings and private residences served by either treated municipal or individual groundwater well systems. Bacteriological quality was assessed including detection of fecal coliform bacteria and heterotrophic plate count (HPC) as well as three potentially pathogenic bacterial genera, Mycobacterium, Legionella, and Helicobacter. All three target genera were detected in drinking water systems on the Crow Reservation. Species detected included the opportunistic and frank pathogens Mycobacterium avium, Mycobacterium gordonae, Mycobacterium flavescens, Legionella pneumophila, and Helicobacter pylori. Additionally, there was an association between HPC bacteria and the presence of Mycobacterium and Legionella but not the presence of Helicobacter. This research has shown that groundwater and municipal drinking water systems on the Crow Reservation can harbor potential bacterial pathogens.

Weak Organic Acids Decrease Borrelia burgdorferi Cytoplasmic pH, Eliciting an Acid Stress Response and Impacting RpoN- and RpoS-Dependent Gene Expression.

The spirochete Borrelia burgdorferi survives in its tick vector, Ixodes scapularis, or within various hosts. To transition between and survive in these distinct niches, B. burgdorferi changes its gene expression in response to environmental cues, both biochemical and physiological. Exposure of B. burgdorferi to weak monocarboxylic organic acids, including those detected in the blood meal of fed ticks, decreased the cytoplasmic pH of B. burgdorferi in vitro. A decrease in the cytoplasmic pH induced the expression of genes encoding enzymes that have been shown to restore pH homeostasis in other bacteria. These include putative coupled proton/cation exchangers, a putative Na+/H+ antiporter, a neutralizing buffer transporter, an amino acid deaminase and a proton exporting vacuolar-type VoV1 ATPase. Data presented in this report suggested that the acid stress response triggered the expression of RpoN- and RpoS-dependent genes including important virulence factors such as outer surface protein C (OspC), BBA66, and some BosR (Borrelia oxidative stress regulator)-dependent genes. Because the expression of virulence factors, like OspC, are so tightly connected by RpoS to general cellular stress responses and cell physiology, it is difficult to separate transmission-promoting conditions in what is clearly a multifactorial and complex regulatory web.

Acetyl-Phosphate Is Not a Global Regulatory Bridge between Virulence and Central Metabolism in Borrelia burgdorferi.

In B. burgdorferi, the Rrp2-RpoN-RpoS signaling cascade is a distinctive system that coordinates the expression of virulence factors required for successful transition between its arthropod vector and mammalian hosts. Rrp2 (BB0763), an RpoN specific response regulator, is essential to activate this regulatory pathway. Previous investigations have attempted to identify the phosphate donor of Rrp2, including the cognate histidine kinase, Hk2 (BB0764), non-cognate histidine kinases such as Hk1, CheA1, and CheA2, and small molecular weight P-donors such as carbamoyl-phosphate and acetyl-phosphate (AcP). In a report by Xu et al., exogenous sodium acetate led to increased expression of RpoS and OspC and it was hypothesized this effect was due to increased levels of AcP via the enzyme AckA (BB0622). Genome analyses identified only one pathway that could generate AcP in B. burgdorferi: the acetate/mevalonate pathway that synthesizes the lipid, undecaprenyl phosphate (C55-P, lipid I), which is essential for cell wall biogenesis. To assess the role of AcP in Rrp2-dependent regulation of RpoS and OspC, we used a unique selection strategy to generate mutants that lacked ackA (bb0622: acetate to AcP) or pta (bb0589: AcP to acetyl-CoA). These mutants have an absolute requirement for mevalonate and demonstrate that ackA and pta are required for cell viability. When the ΔackA or Δpta mutant was exposed to conditions (i.e., increased temperature or cell density) that up-regulate the expression of RpoS and OspC, normal induction of those proteins was observed. In addition, adding 20mM acetate or 20mM benzoate to the growth media of B. burgdorferi strain B31 ΔackA induced the expression of RpoS and OspC. These data suggest that AcP (generated by AckA) is not directly involved in modulating the Rrp2-RpoN-RpoS regulatory pathway and that exogenous acetate or benzoate are triggering an acid stress response in B. burgdorferi.

Optimizing the growth of stressed Helicobacter pylori.

Helicobacter pylori is a gram-negative bacterium that colonizes the human stomach and is responsible for causing gastric ulcers. H. pylori is known to become stressed and nonculturable after exposure to unfavorable conditions. In this study, we enhanced previously published resuscitation procedures, characterized conditions under which stressed H. pylori can be recovered, and formulated a selective and differential resuscitation medium. Results showed that a specialized broth supplemented with trace minerals and lysed human erythrocytes and serum is required for the recovery of nonculturable H. pylori. The type of stress was an important factor in the efficacy of resuscitation, with cells exposed to atmospheric oxygen more readily resuscitated than nutrient deprived cells. After resuscitation, culturable cells were recovered from previously nonculturable oxygen stressed cells (24 and 72 h of exposure) and nonculturable nutrient deprived cells (24 h of exposure). The length of time the cells were exposed to the stress was also an important factor in the recovery of stressed H. pylori. RNA levels were quantified and transcription of the cell division related gene, cdrA (HP0066), was assessed by qRT-PCR. The low levels of RNA detected in stressed cells, after resuscitation, support the idea that a small population of viable cells may be responsible for the colonies recovered on solid agar. The modification of the resuscitation broth into a selective and differential slant culture medium also allowed the recovery of stressed H. pylori. The methods presented here highlight the benefits and limitations of using human blood products for recovering nonculturable H. pylori.

Community-based participatory research in Indian country: improving health through water quality research and awareness.

Water has always been held in high respect by the Apsaálooke (Crow) people of Montana. Tribal members questioned the health of the rivers and well water because of visible water quality deterioration and potential connections to illnesses in the community. Community members initiated collaboration among local organizations, the tribe, and academic partners, resulting in genuine community-based participatory research. The article shares what we have learned as tribal members and researchers about working together to examine surface and groundwater contaminants, assess routes of exposure, and use our data to bring about improved health of our people and our waters.