Pyruvate protects pathogenic spirochetes from H2O2 killing

Assessment of the hypothetical protein BB0616 in the murine infection of Borrelia burgdorferi

bb0616 of Borrelia burgdorferi, the Lyme disease pathogen, encodes a hypothetical protein of unknown function. In this study, we showed that BB0616 was not surface-exposed or associated with the membrane through localization analyses using proteinase K digestion and cell partitioning assays. The expression of bb0616 was influenced by a reduced pH but not by growth phases, elevated temperatures, or carbon sources during in vitro cultivation. A transcriptional start site for bb0616 was identified by using 5' rapid amplification of cDNA ends, which led to the identification of a functional promoter in the 5' regulatory region upstream of bb0616. By analyzing a bb0616-deficient mutant and its isogenic complemented counterparts, we found that the infectivity potential of the mutant was significantly attenuated. The inactivation of bb0616 displayed no effect on borrelial growth in the medium or resistance to oxidative stress, but the mutant was significantly more susceptible to osmotic stress. In addition, the production of global virulence regulators such as BosR and RpoS as well as virulence-associated outer surface lipoproteins OspC and DbpA was reduced in the mutant. These phenotypes were fully restored when gene mutation was complemented with a wild-type copy of bb0616. Based on these findings, we concluded that the hypothetical protein BB0616 is required for the optimal infectivity of B. burgdorferi, potentially by impacting B. burgdorferi virulence gene expression as well as survival of the spirochete under stressful conditions.

Proteomic profile of naturally released extracellular vesicles secreted from Leptospira interrogans serovar Pomona in response to temperature and osmotic stresses

Bacterial extracellular vesicles (EVs) are generally formed by pinching off outer membrane leaflets while simultaneously releasing multiple active molecules into the external environment. In this study, we aimed to identify the protein cargo of leptospiral EVs released from intact leptospires grown under three different conditions: EMJH medium at 30 °C, temperature shifted to 37 °C, and physiologic osmolarity (EMJH medium with 120 mM NaCl). The naturally released EVs observed under transmission electron microscopy were spherical in shape with an approximate diameter of 80-100 nm. Quantitative proteomics and bioinformatic analysis indicated that the EVs were formed primarily from the outer membrane and the cytoplasm. The main functional COG categories of proteins carried in leptospiral EVs might be involved in cell growth, survival and adaptation, and pathogenicity. Relative to their abundance in EVs grown in EMJH medium at 30 °C, 39 and 69 proteins exhibited significant changes in response to the temperature shift and the osmotic change, respectively. During exposure to both stresses, Leptospira secreted several multifunctional proteins via EVs, while preserving certain virulence proteins within whole cells. Therefore, leptospiral EVs may serve as a decoy structure for host responses, whereas some virulence factors necessary for direct interaction with the host environment are reserved in leptospiral cells. This knowledge will be useful for understanding the pathogenesis of leptospirosis and developing as one of vaccine platforms against leptospirosis in the future.

PERK-mediated antioxidant response is key for pathogen persistence in ticks

A crucial phase in the life cycle of tick-borne pathogens is the time spent colonizing and persisting within the arthropod. Tick immunity is emerging as a key force shaping how transmissible pathogens interact with the vector. How pathogens remain in the tick despite immunological pressure remains unknown. In persistently infected Ixodes scapularis, we found that Borrelia burgdorferi (causative agent of Lyme disease) and Anaplasma phagocytophilum (causative agent of granulocytic anaplasmosis) activate a cellular stress pathway mediated by the endoplasmic reticulum receptor PKR-like ER kinase (PERK) and the central regulatory molecule eIF2α. Disabling the PERK pathway through pharmacological inhibition and RNA interference (RNAi) significantly decreased microbial numbers. In vivo RNAi of the PERK pathway not only reduced the number of A. phagocytophilum and B. burgdorferi colonizing larvae after a bloodmeal but also significantly reduced the number of bacteria that survive the molt. An investigation into PERK pathway-regulated targets revealed that A. phagocytophilum and B. burgdorferi induce activity of the antioxidant response regulator, nuclear factor erythroid 2-related factor 2 (Nrf2). Tick cells deficient for nrf2 expression or PERK signaling showed accumulation of reactive oxygen and nitrogen species in addition to reduced microbial survival. Supplementation with antioxidants rescued the microbicidal phenotype caused by blocking the PERK pathway. Altogether, our study demonstrates that the Ixodes PERK pathway is activated by transmissible microbes and facilitates persistence in the arthropod by potentiating an Nrf2-regulated antioxidant environment. IMPORTANCE Recent advances demonstrate that the tick immune system recognizes and limits the pathogens they transmit. Innate immune mediators such as antimicrobial peptides and reactive oxygen/nitrogen species are produced and restrict microbial survival. It is currently unclear how pathogens remain in the tick, despite this immune assault. We found that an antioxidant response controlled by the PERK branch of the unfolded protein response is activated in ticks that are persistently infected with Borrelia burgdorferi (Lyme disease) or Anaplasma phagocytophilum (granulocytic anaplasmosis). The PERK pathway induces the antioxidant response transcription factor, Nrf2, which coordinates a gene network that ultimately neutralizes reactive oxygen and nitrogen species. Interfering with this signaling cascade in ticks causes a significant decline in pathogen numbers. Given that innate immune products can cause collateral damage to host tissues, we speculate that this is an arthropod-driven response aimed at minimizing damage to "self" that also inadvertently benefits the pathogen. Collectively, our findings shed light on the mechanistic push and pull between tick immunity and pathogen persistence within the arthropod vector.

PERK-mediated antioxidant response is key for pathogen persistence in ticks

A crucial phase in the lifecycle of tick-borne pathogens is the time spent colonizing and persisting within the arthropod. Tick immunity is emerging as a key force shaping how transmissible pathogens interact with the vector. How pathogens remain in the tick despite immunological pressure remains unknown. In persistently infected Ixodes scapularis , we found that Borrelia burgdorferi (Lyme disease) and Anaplasma phagocytophilum (granulocytic anaplasmosis) activate a cellular stress pathway mediated by the endoplasmic reticulum receptor PERK and the central regulatory molecule, eIF2α. Disabling the PERK pathway through pharmacological inhibition and RNAi significantly decreased microbial numbers. In vivo RNA interference of the PERK pathway not only reduced the number of A. phagocytophilum and B. burgdorferi colonizing larvae after a bloodmeal, but also significantly reduced the number of bacteria that survive the molt. An investigation into PERK pathway-regulated targets revealed that A. phagocytophilum and B. burgdorferi induce activity of the antioxidant response regulator, Nrf2. Tick cells deficient for nrf2 expression or PERK signaling showed accumulation of reactive oxygen and nitrogen species in addition to reduced microbial survival. Supplementation with antioxidants rescued the microbicidal phenotype caused by blocking the PERK pathway. Altogether, our study demonstrates that the Ixodes PERK pathway is activated by transmissible microbes and facilitates persistence in the arthropod by potentiating an Nrf2-regulated antioxidant environment.

Immune evasion strategies of major tick-transmitted bacterial pathogens

Tick-transmitted bacterial pathogens thrive in enzootic infection cycles, colonizing disparate vertebrate and arthropod tissues, often establishing persistent infections. Therefore, the evolution of robust immune evasion strategies is central to their successful persistence or transmission between hosts. To survive in nature, these pathogens must counteract a broad range of microbicidal host responses that can be localized, tissue-specific, or systemic, including a mix of these responses at the host-vector interface. Herein, we review microbial immune evasion strategies focusing on Lyme disease spirochetes and rickettsial or tularemia agents as models for extracellular and intracellular tick-borne pathogens, respectively. A better understanding of these adaptive strategies could enrich our knowledge of the infection biology of relevant tick-borne diseases, contributing to the development of future preventions.

Enhanced Hemolytic Activity of Mesophilic Aeromonas salmonicida SRW-OG1 Is Brought about by Elevated Temperatures

Aeromonas salmonicida is a well-known cold-water pathogenic bacterium. Previously, we reported the first isolation of pathogenic A. salmonicida from diseased Epinephelus coioides, a kind of warm-water fish, and it was proved to be a putative mesophilic strain with potent pathogenicity to humans. In order to investigate the mechanisms underlying mesophilic growth ability and virulence, the transcriptome of A. salmonicida SRW-OG1 at 18, 28, and 37 °C was analyzed. The transcriptome of A. salmonicida SRW-OG1 at different temperatures showed a clear separation boundary, which might provide valuable information for the temperature adaptation and virulence regulation of A. salmonicida SRW-OG1. Interestingly, aerA and hlyA, the hemolytic genes encoding aerolysin and hemolysin, were found to be significantly up-regulated at 28 and 37 °C. Since aerolysin and hemolysin are the most well-known and -characterized virulence factors of pathogenic Aeromonas strains, the induction of aerA and hlyA was associated with the mesophilic virulence. Further study proved that the extracellular products (ECPs) purchased from A. salmonicida SRW-OG1 cultured at 28 and 37 °C showed elevated hemolytic activity and virulence than those at 18 °C. Moreover, the silence of aerA and hlyA led to significantly decreased hemolysis and virulence. Taken together, our results revealed that the mesophilic virulence of A. salmonicida SRW-OG1 might be due to the enhanced expression of aerA and hlyA induced by elevated temperatures.

BB0761, a MepM homolog, contributes to Borrelia burgdorferi cell division and mammalian infectivity

M23 family endopeptidases play important roles in cell division and separation in a wide variety of bacteria. Recent studies have suggested that these proteins also contribute to bacterial virulence. However, the biological function of M23 peptidases in pathogenic spirochetes remains unexplored. Here, we describe Borrelia burgdorferi, the bacterial pathogen causing Lyme disease, requires a putative M23 family homolog, BB0761, for spirochete morphology and cell division. Indeed, the inactivation of bb0761 led to an aberrant filamentous phenotype as well as the impairment of B. burgdorferi growth in vitro. These phenotypes were complemented not only with B. burgdorferi bb0761, but also with the mepM gene from E. coli. Moreover, the bb0761 mutant showed a complete loss of infectivity in a murine model of Lyme borreliosis. Resistance of the mutant to osmotic and oxidative stresses was markedly reduced. Our combined results indicate that BB0761 contributes to B. burgdorferi cell division and virulence.

Comparison of transcriptional profiles of Treponema pallidum during experimental infection of rabbits and in vitro culture: Highly similar, yet different

Treponema pallidum ssp. pallidum, the causative agent of syphilis, can now be cultured continuously in vitro utilizing a tissue culture system, and the multiplication rates are similar to those obtained in experimental infection of rabbits. In this study, the RNA transcript profiles of the T. pallidum Nichols during in vitro culture and rabbit infection were compared to examine whether gene expression patterns differed in these two environments. To this end, RNA preparations were converted to cDNA and subjected to RNA-seq using high throughput Illumina sequencing; reverse transcriptase quantitative PCR was also performed on selected genes for validation of results. The transcript profiles in the in vivo and in vitro environments were remarkably similar, exhibiting a high degree of concordance overall. However, transcript levels of 94 genes (9%) out of the 1,063 predicted genes in the T. pallidum genome were significantly different during rabbit infection versus in vitro culture, varying by up to 8-fold in the two environments. Genes that exhibited significantly higher transcript levels during rabbit infection included those encoding multiple ribosomal proteins, several prominent membrane proteins, glycolysis-associated enzymes, replication initiator DnaA, rubredoxin, thioredoxin, two putative regulatory proteins, and proteins associated with solute transport. In vitro cultured T. pallidum had higher transcript levels of DNA repair proteins, cofactor synthesis enzymes, and several hypothetical proteins. The overall concordance of the transcript profiles may indicate that these environments are highly similar in terms of their effects on T. pallidum physiology and growth, and may also reflect a relatively low level of transcriptional regulation in this reduced genome organism.

First insights into a pyruvate sensing and uptake system in Vibrio campbellii and its importance for virulence

Pyruvate is a key metabolite in living cells and has been shown to play a crucial role in the virulence of several bacterial pathogens. The bioluminescent Vibrio campbellii, a severe infectious burden for marine aquaculture, excretes extraordinarily large amounts of pyruvate during growth and rapidly retrieves it by an as-yet unknown mechanism. We have now identified the responsible pyruvate transporter, here named BtsU, and our results show that it is the only pyruvate transporter in V. campbellii. Expression of btsU is tightly regulated by the membrane-integrated LytS-type histidine kinase BtsS, a sensor for extracellular pyruvate, and the LytTR-type response regulator BtsR. Cells lacking either the pyruvate transporter or sensing system show no chemotactic response towards pyruvate, indicating that intracellular pyruvate is required to activate the chemotaxis system. Moreover, pyruvate sensing and uptake were found to be important for the resuscitation of V. campbellii from the viable but nonculturable (VBNC) state and the bacterium's virulence against brine shrimp larvae. IMPORTANCE Bacterial infections are a serious threat to marine aquaculture, one of the fastest growing food sectors on earth. Therefore, it is extremely important to learn more about the pathogens responsible, one of which is Vibrio campbellii. This study sheds light on the importance of pyruvate sensing and uptake for V. campbellii, and reveals that the bacterium possesses only one pyruvate transporter, which is activated by a pyruvate-responsive histidine kinase/response regulator system. Without the ability to sense or take up pyruvate, the virulence of V. campbellii towards gnotobiotic brine shrimp larvae is strongly reduced.

The Diadenylate Cyclase CdaA Is Critical for Borrelia turicatae Virulence and Physiology

Relapsing fever (RF), caused by spirochetes of the genus Borrelia, is a globally distributed, vector-borne disease with high prevalence in developing countries. To date, signaling pathways required for infection and virulence of RF Borrelia spirochetes are unknown. Cyclic di-AMP (c-di-AMP), synthesized by diadenylate cyclases (DACs), is a second messenger predominantly found in Gram-positive organisms that is linked to virulence and essential physiological processes. Although Borrelia is Gram-negative, it encodes one DAC (CdaA), and its importance remains undefined. To investigate the contribution of c-di-AMP signaling in the RF bacterium Borrelia turicatae, a cdaA mutant was generated. The mutant was significantly attenuated during murine infection, and genetic complementation reversed this phenotype. Because c-di-AMP is essential for viability in many bacteria, whole-genome sequencing was performed on cdaA mutants, and single-nucleotide polymorphisms identified potential suppressor mutations. Additionally, conditional mutation of cdaA confirmed that CdaA is important for normal growth and physiology. Interestingly, mutation of cdaA did not affect expression of homologs of virulence regulators whose levels are impacted by c-di-AMP signaling in the Lyme disease bacterium Borrelia burgdorferi Finally, the cdaA mutant had a significant growth defect when grown with salts, at decreased osmolarity, and without pyruvate. While the salt treatment phenotype was not reversed by genetic complementation, possibly due to suppressor mutations, growth defects at decreased osmolarity and in media lacking pyruvate could be attributed directly to cdaA inactivation. Overall, these results indicate CdaA is critical for B. turicatae pathogenesis and link c-di-AMP to osmoregulation and central metabolism in RF spirochetes.

Borrelia burgdorferi infection modifies protein content in saliva of Ixodes scapularis nymphs

BACKGROUND

Lyme disease (LD) caused by Borrelia burgdorferi is the most prevalent tick-borne disease. There is evidence that vaccines based on tick proteins that promote tick transmission of B. burgdorferi could prevent LD. As Ixodes scapularis nymph tick bites are responsible for most LD cases, this study sought to identify nymph tick saliva proteins associated with B. burgdorferi transmission using LC-MS/MS. Tick saliva was collected using a non-invasive method of stimulating ticks (uninfected and infected: unfed, and every 12 h during feeding through 72 h, and fully-fed) to salivate into 2% pilocarpine-PBS for protein identification using LC-MS/MS.

RESULTS

We identified a combined 747 tick saliva proteins of uninfected and B. burgdorferi infected ticks that were classified into 25 functional categories: housekeeping-like (48%), unknown function (18%), protease inhibitors (9%), immune-related (6%), proteases (8%), extracellular matrix (7%), and small categories that account for <5% each. Notably, B. burgdorferi infected ticks secreted high number of saliva proteins (n=645) than uninfected ticks (n=376). Counter-intuitively, antimicrobial peptides, which function to block bacterial infection at tick feeding site were suppressed 23-85 folds in B. burgdorferi infected ticks. Similar to glycolysis enzymes being enhanced in mammalian cells exposed to B. burgdorferi : eight of the 10-glycolysis pathway enzymes were secreted at high abundance by B. burgdorferi infected ticks. Of significance, rabbits exposed to B. burgdorferi infected ticks acquired potent immunity that caused 40-60% mortality of B. burgdorferi infected ticks during the second infestation compared to 15-28% for the uninfected. This might be explained by ELISA data that show that high expression levels of immunogenic proteins in B. burgdorferi infected ticks.

CONCLUSION

Data here suggest that B. burgdorferi infection modified protein content in tick saliva to promote its survival at the tick feeding site. For instance, enzymes; copper/zinc superoxide dismutase that led to production of H2O2 that is toxic to B. burgdorferi were suppressed, while, catalase and thioredoxin that neutralize H2O2, and pyruvate kinase which yields pyruvate that protects Bb from H2O2 killing were enhanced. We conclude data here is an important resource for discovery of effective antigens for a vaccine to prevent LD.

The Lon-1 Protease Is Required by Borrelia burgdorferi To Infect the Mammalian Host

Borrelia burgdorferi encodes a functional homolog of canonical Lon protease termed Lon-2. In addition, B. burgdorferi encodes a second Lon homolog called Lon-1. Recent studies suggest that Lon-1 may function differently from the prototypical Lon protease. However, the function of Lon-1 in B. burgdorferi biology remains virtually unknown. Particularly, the contribution of Lon-1 to B. burgdorferi fitness and infection remains hitherto unexplored. Herein, we show that Lon-1 plays a critical role for the infection of B. burgdorferi in a mammalian host. We found that lon-1 was highly expressed during animal infection, implying an important function of this protein in bacterial infection. We further generated a lon-1 deletion mutant and an isogenic complemented strain. Relative to that of the wild-type strain, the infectivity of the mutant was severely attenuated in a murine infection model. Our data also showed that the mutant displayed growth defects in regular BSK-II medium. Furthermore, bacterial resistance to osmotic stress was markedly reduced when lon-1 was inactivated. When exposed to tert-butyl hydroperoxide, survival of the lon-1 mutant was impaired. In addition, production of several virulence factors, such as BosR, RpoS, and OspC, was elevated in the mutant. These phenotypes were restored when the lon-1 mutation was complemented. Finally, we created a lon-1(S714A) mutant and found that this mutant failed to infect mice, suggesting that the proteolytic activity of Lon-1 is essential for bacterial infection. Taken together, these results demonstrate that Lon-1 is required by B. burgdorferi to infect animal hosts and to cope with environmental stresses.

Pyruvate secretion by oral streptococci modulates hydrogen peroxide dependent antagonism

Many commensal oral streptococci generate H₂O₂ via pyruvate oxidase (SpxB) to inhibit the growth of competing bacteria like Streptococcus mutans, a major cariogenic species. In Streptococcus sanguinis SK36 (SK36) and Streptococcus gordonii DL1 (DL1), spxB expression and H₂O₂ release are subject to carbon catabolite repression by the catabolite control protein A (CcpA). Surprisingly, ccpA deletion mutants of SK36 and DL1 fail to inhibit S. mutans despite their production of otherwise inhibitory levels of H₂O₂. Using H₂O₂-deficient spxB deletion mutants of SK36 and DL1, it was subsequently discovered that both strains confer protection in trans to other bacteria when H₂O₂ is added exogenously. This protective effect depends on the direct detoxification of H₂O₂ by the release of pyruvate. The pyruvate dependent protective effect is also present in other spxB-encoding streptococci, such as the pneumococcus, but is missing from spxB-negative species like S. mutans. Targeted and transposon-based mutagenesis revealed Nox (putative H₂O-forming NADH dehydrogenase) as an essential component required for pyruvate release and oxidative protection, while other genes such as sodA and dps play minor roles. Furthermore, pyruvate secretion is only detectable in aerobic growth conditions at biofilm-like cell densities and is responsive to CcpA-dependent catabolite control. This ability of spxB-encoding streptococci reveals a new facet of the competitive interactions between oral commensals and pathobionts and provides a mechanistic basis for the variable levels of inhibitory potential observed among H₂O₂-producing strains of commensal oral streptococci.

Borrelia burgdorferi hijacks cellular metabolism of immune cells: Consequences for host defense

Changes in cellular metabolism have proven to be important factors in driving cell behavior. It has been shown that cellular metabolism of immune cells changes when exposed to or infected by several pathogens: while this is often an adaptation of the host cells to the infection, sometimes it represents a mechanism through which the pathogens evade immune activation. Borrelia burgdorferi sensu lato, the causative agent of Lyme borreliosis, is a pathogen that highly depends on the host to survive, as the bacterium lacks many central metabolic pathways to generate its own nutrients. It is therefore quite likely that the bacterium interacts with host cells to obtain these metabolites and thereby affects metabolism in the host. Previously, several studies have assessed metabolic pathways in B. burgdorferi s.l. and how it adapts to its different host species. However, few studies have looked into how the interaction with the bacterium might affect the host cell metabolism. In this review we present the major metabolic pathways activated during Lyme borreliosis, viewed from both bacterium and host metabolism, and we discuss how these pathways interact with each other, and how they influence pathogenesis of Lyme borreliosis.

The Lon-2 protease of Borrelia burgdorferi is critical for infection in the mammalian host

Borrelia burgdorferi encodes a functional homolog of canonical Lon protease termed Lon-2. To date, the contribution of Lon-2 to B. burgdorferi fitness and infection remains unexplored. Herein, we showed that expression of lon-2 was highly induced during animal infection, suggesting that Lon-2 is important for B. burgdorferi infection. We further generated a lon-2 deletion mutant. Compared with that of wild-type (WT) strain, the infectivity of the mutant was severely attenuated in a murine infection model. Although no growth defect was observed for the mutant in normal BSK-II medium, resistance of the lon-2 mutant to osmotic stress was markedly reduced. In addition, when exposed to tert-Butyl hydroperoxide, survival of the lon-2 mutant was impaired. In addition, we found that the protein levels of RpoS and RpoS-dependent OspC were decreased in the mutant. All these phenotypes were restored to WT or near-WT levels when lon-2 mutation was complemented in cis. Taken together, these results demonstrate that Lon-2 is critical for B. burgdorferi to establish infection and to cope with environmental stresses. This study provides a foundation for further uncovering the direct link between the dual roles of Lon-2 in protein quality control and bacterial pathogenesis.

Assessing the Contribution of an HtrA Family Serine Protease During Borrelia turicatae Mammalian Infection

Tick-borne relapsing fever (TBRF), characterized by recurring febrile episodes, is globally distributed and among the most common bacterial infections in some African countries. Despite the public health concern that this disease represents, little is known regarding the virulence determinants required by TBRF Borrelia during infection. Because the chromosomes of TBRF Borrelia show extensive colinearity with those of Lyme disease (LD) Borrelia, the exceptions represent unique genes encoding proteins that are potentially essential to the disparate enzootic cycles of these two groups of spirochetes. One such exception is a gene encoding an HtrA family protease, BtpA, that is present in TBRF Borrelia, but not in LD spirochetes. Previous work suggested that btpA orthologs may be important for resistance to stresses faced during mammalian infection. Herein, proteomic analyses of the TBRF spirochete, Borrelia turicatae, demonstrated that BtpA, as well as proteins encoded by adjacent genes in the B. turicatae genome, were produced in response to culture at mammalian body temperature, suggesting a role in mammalian infection. Further, transcriptional analyses revealed that btpA was expressed with the genes immediately upstream and downstream as part of an operon. To directly assess if btpA is involved in resistance to environmental stresses, btpA deletion mutants were generated. btpA mutants demonstrated no growth defect in response to heat shock, but were more sensitive to oxidative stress produced by t-butyl peroxide compared to wild-type B. turicatae. Finally, btpA mutants were fully infectious in a murine relapsing fever (RF) infection model. These results indicate that BtpA is either not required for mammalian infection, or that compensatory mechanisms exist in TBRF spirochetes to combat environmental stresses encountered during mammalian infection in the absence of BtpA.

The relapsing fever spirochete Borrelia turicatae persists in the highly oxidative environment of its soft-bodied tick vector

The relapsing fever spirochete Borrelia turicatae possesses a complex life cycle in its soft-bodied tick vector, Ornithodoros turicata. Spirochetes enter the tick midgut during a blood meal, and, during the following weeks, spirochetes disseminate throughout O. turicata. A population persists in the salivary glands allowing for rapid transmission to the mammalian hosts during tick feeding. Little is known about the physiological environment within the salivary glands acini in which B. turicatae persists. In this study, we examined the salivary gland transcriptome of O. turicata ticks and detected the expression of 57 genes involved in oxidant metabolism or antioxidant defences. We confirmed the expression of five of the most highly expressed genes, including glutathione peroxidase (gpx), thioredoxin peroxidase (tpx), manganese superoxide dismutase (sod-1), copper-zinc superoxide dismutase (sod-2), and catalase (cat) by reverse-transcriptase droplet digital polymerase chain reaction (RT-ddPCR). We also found distinct differences in the expression of these genes when comparing the salivary glands and midguts of unfed O. turicata ticks. Our results indicate that the salivary glands of unfed O. turicata nymphs are highly oxidative environments where reactive oxygen species (ROS) predominate, whereas midgut tissues comprise a primarily nitrosative environment where nitric oxide synthase is highly expressed. Additionally, B. turicatae was found to be hyperresistant to ROS compared with the Lyme disease spirochete Borrelia burgdorferi, suggesting it is uniquely adapted to the highly oxidative environment of O. turicata salivary gland acini.

Electrical discharges in water induce spores' DNA damage

Bacterial spores are one of the most resilient life forms on earth and are involved in many human diseases, such as infectious diarrhea, fatal paralytic illnesses and respiratory infections. Here, we investigated the mechanisms involved in the death of Bacillus pumilus spores after exposure to electric arcs in water. Cutting-edge microscopies at the nanoscale did not reveal any structural disorganization of spores exposed to electric arcs. This result suggested the absence of physical destruction by a propagating shock wave or an exposure to an electric field. However, Pulsed-Field Gel Electrophoresis (PFGE) revealed genomic DNA damage induced by UV radiation and Reactive Oxygen Species (ROS). UV induced single-strand DNA breaks and thymine dimers while ROS were mainly involved in base excision. Our findings revealed a correlation between DNA damage and the treatment of spores with electrical discharges.

The oligopeptide ABC transporter OppA4 negatively regulates the virulence factor OspC production of the Lyme disease pathogen

Borrelia burgdorferi sensu lato, the agent of Lyme disease, exists in nature through a complex enzootic life cycle that involves both ticks and mammals. The B. burgdorferi genome encodes five Oligopeptide ABC transporters (Opp) that are predicted to be involve in transport of various nutrients. Previously, it was reported that OppA5 is important for the optimal production of OspC, a major virulence factor of B. burgdorferi. In this study, possible role of another Oligopeptide ABC transporter, OppA4 in ospC expression was investigated by construction of an oppA4 deletion mutant and the complemented strain. Inactivation of oppA4 resulted an increased production of OspC, suggesting that OppA4 has a negative impact on ospC expression. Expression of ospC is controlled by Rrp2-RpoN-RpoS, the central pathway essential for mammal infection. We showed that increased ospC expression in the oppA4 mutant was due to an increased rpoS expression. We then further investigated how OppA4 negatively regulates this pathway. Two regulators, BosR and BadR, are known to positively and negatively, respectively, regulate the Rrp2-RpoN-RpoS pathway. We found that deletion of oppA4 resulted in an increased level of BosR. Previous reports showed that bosR is mainly regulated at the post-transcriptional level by other factors. However, OppA4 appears to negatively regulate bosR expression at the transcriptional level. The finding of OppA4 involved in regulation of the Rrp2-RpoN-RpoS pathway further reinforces the importance of nutritional virulence to the enzootic cycle of B. burgdorferi.

Stimulation of Vibrio vulnificus Pyruvate Kinase in the Presence of Glucose to Cope With H2O2 Stress Generated by Its Competitors

The bacterial phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system (PTS) regulates a variety of cellular processes in addition to catalyzing the coupled transport and phosphorylation of carbohydrates. We recently reported that, in the presence of glucose, HPr of the PTS is dephosphorylated and interacts with pyruvate kinase A (PykA) catalyzing the conversion of PEP to pyruvate in Vibrio vulnificus. Here, we show that this interaction enables V. vulnificus to survive H₂O₂ stress by increasing pyruvate production. A pykA deletion mutant was more susceptible to H₂O₂ stress than wild-type V. vulnificus without any decrease in the expression level of catalase, and this sensitivity was rescued by the addition of pyruvate. The H₂O₂ sensitivity difference between wild-type and pykA mutant strains becomes more apparent in the presence of glucose. Fungi isolated from the natural habitat of V. vulnificus retarded the growth of the pykA mutant more severely than the wild-type strain in the presence of glucose by glucose oxidase-dependent generation of H₂O₂. These data suggest that V. vulnificus has evolved to resist the killing action of its fungal competitors by increasing pyruvate production in the presence of glucose.

Improved measurements of scant hydrogen peroxide enable experiments that define its threshold of toxicity for Escherichia coli

Escherichia coli is a model organism that has been exploited to reveal key details of hydrogen peroxide stress: the biomolecules that H₂O₂ most rapidly damages and the defensive tactics that organisms use to fend it off. Much less clear is the amount of exogenous H₂O₂ that is sufficient to injure the bacterium and/or to trigger its stress response. To fill this gap, we need to study the behavior of cells when they are exposed to defined amounts of H₂O₂ on an hours-long time scale. Such experiments are difficult because bacteria rapidly consume H₂O₂ that is added to test cultures. Further, lab media itself can generate H₂O₂, and media components interfere with the quantification of H₂O₂ levels. In this study we describe mechanisms by which media components interfere with H₂O₂ determinations, and we identify simple ways to minimize and correct for this interference. Using these techniques, it was shown that standard media generate so much H₂O₂ that most intracellular H₂O₂ derives from the medium rather than from endogenous metabolism. Indeed, bacteria spread on plates must induce their stress response or else perish. Finally, two straightforward methods were used to sustain low-micromolar steady-state concentrations of H₂O₂. In this way we determined that > 2 μM extracellular H₂O₂ is sufficient to trigger the intracellular OxyR stress response, and > 5 μM begins to impair cell growth in a minimal medium. These concentrations are orders of magnitude lower than the doses that have typically been used in lab experiments. The new approaches should enable workers to study how various organisms cope with natural levels of H₂O₂ stress.

Degradation of hydrogen peroxide at the ocean's surface: the influence of the microbial community on the realized thermal niche of Prochlorococcus

Prochlorococcus, the smallest and most abundant phytoplankter in the ocean, is highly sensitive to hydrogen peroxide (HOOH), and co-occurring heterotrophs such as Alteromonas facilitate the growth of Prochlorococcus by scavenging HOOH. Temperature is also a major influence on Prochlorococcus abundance and distribution in the ocean, and studies in other photosynthetic organisms have shown that HOOH and temperature extremes can act together as synergistic stressors. To address potential synergistic effects of temperature and HOOH on Prochlorococcus growth, high- and low-temperature-adapted representative strains were cultured at ecologically relevant concentrations under a range of HOOH concentrations and temperatures. Higher concentrations of HOOH severely diminished the permissive temperature range for growth of both Prochlorococcus strains. At the permissive temperatures, the growth rates of both Prochlorococcus strains decreased as a function of HOOH, and cold temperature increased susceptibility of photosystem II to HOOH-mediated damage. Serving as a proxy for the natural community, co-cultured heterotrophic bacteria increased the Prochlorococcus growth rate under these temperatures, and expanded the permissive range of temperature for growth. These studies indicate that in the ocean, the cross-protective function of the microbial community may confer a fitness increase for Prochlorococcus at its temperature extremes, especially near the ocean surface where oxidative stress is highest. This interaction may play a substantial role in defining the realized thermal niche and habitat range of Prochlorococcus with respect to latitude.

Optically Assisted Surface Functionalization for Protein Arraying in Aqueous Media

Protein surface patterning is employed in a broad spectrum of applications ranging from protein microarray analysis to 2D cell organization. However, limitations arise because of the highly sensitive nature of proteins requiring careful handling to ensure their structural and functional integrity during the grafting process. Here, we describe a patterning protocol that keeps proteins in an aqueous environment during their immobilization, avoiding the loss of their biological activity. The procedure is based on the UV-mediated removal of polyethylene glycol self-assembled monolayers in a transparent microfluidic chamber, giving access to micrometric motifs of predefined geometries. Afterward, modified proteins can be grafted on the photopatterned domains. We also studied the influence of reactive oxygen species for a better understanding of the chemical mechanism involved in this process. Finally, as a proof of concept, a protein microarray was created with this process using cell-capturing antibodies to immobilize human blood cells, confirming the functionality of the arrayed proteins.

Comparative analysis of methicillin-sensitive and resistant Staphylococcus aureus exposed to emodin based on proteomic profiling

Emodin has a strong antibacterial activity, including methicillin-resistant Staphylococcus aureus (MRSA). However, the mechanism by which emodin induces growth inhibition against MRSA remains unclear. In this study, the isobaric tags for relative and absolute quantitation (iTRAQ) proteomics approach was used to investigate the modes of action of emodin on a MRSA isolate and methicillin-sensitive S. aureus ATCC29213(MSSA). Proteomic analysis showed that expression levels of 145 and 122 proteins were changed significantly in MRSA and MSSA, respectively, after emodin treatment. Comparative analysis of the functions of differentially expressed proteins between the two strains was performed via bioinformatics tools blast2go and STRING database. Proteins related to pyruvate pathway imbalance induction, protein synthesis inhibition, and DNA synthesis suppression were found in both methicillin-sensitive and resistant strains. Moreover, Interference proteins related to membrane damage mechanism were also observed in MRSA. Our findings indicate that emodin is a potential antibacterial agent targeting MRSA via multiple mechanisms.

Comparative analysis of LytS/LytTR-type histidine kinase/response regulator systems in γ-proteobacteria

Bacterial histidine kinase/response regulator systems operate at the interface between environmental cues and physiological states. Escherichia coli contains two LytS/LytTR-type histidine kinase/response regulator systems, BtsS/BtsR (formerly YehU/YehT) and YpdA/YpdB, which have been identified as pyruvate-responsive two-component systems. Since they exhibit remarkable similarity, we analyzed their phylogenetic distribution within the γ-proteobacteria, and experimentally characterized them in a set of representative species. We found that BtsS/BtsR is the predominant LytS/LytTR-type two-component system among γ-proteobacteria, whereas YpdA/YpdB primarily appears in a supplementary role. Based on our observations in E. coli, we used the highly conserved DNA-binding motifs to test the in vivo functionality of both systems in various genera, including Salmonella, Enterobacter, Citrobacter, Xenorhabdus, Yersinia, Aeromonas and Vibrio. The results suggest that, in all cases tested, BtsS/BtsR and YpdA/YpdB respond to different levels of pyruvate in the environment.

A high-throughput genetic screen identifies previously uncharacterized Borrelia burgdorferi genes important for resistance against reactive oxygen and nitrogen species

Borrelia burgdorferi, the causative agent of Lyme disease in humans, is exposed to reactive oxygen and nitrogen species (ROS and RNS) in both the tick vector and vertebrate reservoir hosts. B. burgdorferi contains a limited repertoire of canonical oxidative stress response genes, suggesting that novel gene functions may be important for protection of B. burgdorferi against ROS or RNS exposure. Here, we use transposon insertion sequencing (Tn-seq) to conduct an unbiased search for genes involved in resistance to nitric oxide, hydrogen peroxide, and tertiary-butyl hydroperoxide in vitro. The screens identified 66 genes whose disruption resulted in increased susceptibility to at least one of the stressors. These genes include previously characterized mediators of ROS and RNS resistance (including components of the nucleotide excision repair pathway and a subunit of a riboflavin transporter), as well as novel putative resistance candidates. DNA repair mutants were among the most sensitive to RNS in the Tn-seq screen, and survival assays with individual Tn mutants confirmed that the putative ribonuclease BB0839 is involved in resistance to nitric oxide. In contrast, mutants lacking predicted inner membrane proteins or transporters were among the most sensitive to ROS, and the contribution of three such membrane proteins (BB0017, BB0164, and BB0202) to ROS sensitivity was confirmed using individual Tn mutants and complemented strains. Further analysis showed that levels of intracellular manganese are significantly reduced in the Tn::bb0164 mutant, identifying a novel role for BB0164 in B. burgdorferi manganese homeostasis. Infection of C57BL/6 and gp91phox-/- mice with a mini-library of 39 Tn mutants showed that many of the genes identified in the in vitro screens are required for infectivity in mice. Collectively, our data provide insight into how B. burgdorferi responds to ROS and RNS and suggests that this response is relevant to the in vivo success of the organism.

Major Neutrophilia Observed in Acute Phase of Human Leptospirosis Is Not Associated with Increased Expression of Granulocyte Cell Activation Markers

It has long been known that pathogenic Leptospira can mobilize the immune system but the specific contribution of neutrophils to control the infectious challenge remains to be clarified. We herein analyzed the phenotype of circulating neutrophils of patients with leptospirosis and healthy controls for the expression of toll-like receptor (TLR) type 2 (TLR2, to sense the leptospiral LPS) and several activation markers: interleukin 8 chemokine receptor CD182 (CXCR2), CD11b of the integrin/opsonin complement receptor type 3 (CR3) and CD15 (ligand of the selectin). The plasmatic level of the main CD182 ligand, interleukin 8 (CXCL8), was measured by ELISA. Hospitalized leptospirosis cases showed marked neutrophilia, particularly in the most severe cases. Interestingly, TLR2 was significantly increased in leptospirosis but identical levels of CD182 and CD11b were detected when compared to controls. CD15 was significantly decreased on neutrophils in leptospirosis but returned to normal within 1 month. Basal levels of IL-8 were measured in control subjects and were not increased in leptospirosis cases at the initial stage of the disease. In conclusion, we observed that neutrophils failed to regulate the expression of several of the receptors involved in cell activation and recruitment. This study further emphasizes the paradigm that neutrophils may be impaired in their overall capacity to thwart bacterial infection in leptospirosis patients.

Gene bb0318 Is Critical for the Oxidative Stress Response and Infectivity of Borrelia burgdorferi

A greater understanding of the molecular mechanisms that Borrelia burgdorferi uses to survive during mammalian infection is critical for the development of novel diagnostic and therapeutic tools to improve the clinical management of Lyme disease. By use of an in vivo expression technology (IVET)-based approach to identify B. burgdorferi genes expressed in vivo, we discovered the bb0318 gene, which is thought to encode the ATPase component of a putative riboflavin ABC transport system. Riboflavin is a critical metabolite enabling all organisms to maintain redox homeostasis. B. burgdorferi appears to lack the metabolic capacity for de novo synthesis of riboflavin and so likely relies on scavenging riboflavin from the host environment. In this study, we sought to investigate the role of bb0318 in B. burgdorferi pathogenesis. No in vitro growth defect was observed for the Δbb0318 clone. However, the mutant spirochetes displayed reduced levels of survival when exposed to exogenous hydrogen peroxide or murine macrophages. Spirochetes lacking bb0318 were found to have a 100-fold-higher 50% infectious dose than spirochetes containing bb0318 In addition, at a high inoculum dose, bb0318 was found to be important for effective spirochete dissemination to deep tissues for as long as 3 weeks postinoculation and to be critical for B. burgdorferi infection of mouse hearts. Together, these data implicate bb0318 in the oxidative stress response of B. burgdorferi and indicate the contribution of bb0318 to B. burgdorferi mammalian infectivity.

The Nucleotide Excision Repair Pathway Protects Borrelia burgdorferi from Nitrosative Stress in Ixodes scapularis Ticks

The Lyme disease spirochete Borrelia burgdorferi encounters a wide range of environmental conditions as it cycles between ticks of the genus Ixodes and its various mammalian hosts. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are potent antimicrobial molecules generated during the innate immune response to infection, however, it is unclear whether ROS and RNS pose a significant challenge to B. burgdorferi in vivo. In this study, we screened a library of B. burgdorferi strains with mutations in DNA repair genes for increased susceptibility to ROS or RNS in vitro. Strains with mutations in the methyl-directed mismatch repair gene mutS1 are hypersensitive to killing by ROS, while strains lacking the nucleotide excision repair (NER) gene uvrB show increased susceptibility to both ROS and RNS. Therefore, mutS1-deficient and uvrB-deficient strains were compared for their ability to complete their infectious cycle in Swiss Webster mice and I. scapularis ticks to help identify sites of oxidative and nitrosative stresses encountered by B. burgdorferi in vivo. Both mutS1 and uvrB were dispensable for infection of mice, while uvrB promoted the survival of spirochetes in I. scapularis ticks. The decreased survival of uvrB-deficient B. burgdorferi was associated with the generation of RNS in I. scapularis midguts and salivary glands during feeding. Collectively, these data suggest that B. burgdorferi must withstand cytotoxic levels of RNS produced during infection of I. scapularis ticks.

Interaction of Bovine Peripheral Blood Polymorphonuclear Cells and Leptospira Species; Innate Responses in the Natural Bovine Reservoir Host

Cattle are the reservoir hosts of Leptospira borgpetersenii serovar Hardjo, and can also be reservoir hosts of other Leptospira species such as L. kirschneri, and Leptospira interrogans. As a reservoir host, cattle shed Leptospira, infecting other animals, including humans. Previous studies with human and murine neutrophils have shown activation of neutrophil extracellular trap or NET formation, and upregulation of inflammatory mediators by neutrophils in the presence of Leptospira. Humans, companion animals and most widely studied models of Leptospirosis are of acute infection, hallmarked by systemic inflammatory response, neutrophilia, and septicemia. In contrast, cattle exhibit chronic infection with few outward clinical signs aside from reproductive failure. Taking into consideration that there is host species variation in innate immunity, especially in pathogen recognition and response, the interaction of bovine peripheral blood polymorphonuclear cells (PMNs) and several Leptospira strains was evaluated. Studies including bovine-adapted strains, human pathogen strains, a saprophyte and inactivated organisms. Incubation of PMNs with Leptospira did induce slight activation of neutrophil NETs, greater than unstimulated cells but less than the quantity from E. coli P4 stimulated PMNs. Very low but significant from non-stimulated, levels of reactive oxygen peroxides were produced in the presence of all Leptospira strains and E. coli P4. Similarly, significant levels of reactive nitrogen intermediaries (NO2) was produced from PMNs when incubated with the Leptospira strains and greater quantities in the presence of E. coli P4. PMNs incubated with Leptospira induced RNA transcripts of IL-1β, MIP-1α, and TNF-α, with greater amounts induced by live organisms when compared to heat-inactivated leptospires. Transcript for inflammatory cytokine IL-8 was also induced, at similar levels regardless of Leptospira strain or viability. However, incubation of Leptospira strains with bovine PMNs did not affect Leptospira viability as measured by limiting dilution culture. This is in contrast to previously reported results of innate inflammatory activation by Leptospira in human and other animal models, or the activation and interaction of bovine PMNs with Escherichia coli and other bacterial pathogens. While it could be hypothesized that variations in innate receptor recognition, specifically variance in toll-like receptor 2, could underlie the observed reduction of activation in bovine PMNs, additional studies would be needed to explore this possibility. Reduction in neutrophil responses may help to establish nearly asymptomatic chronic Leptospira infection of cattle. This study emphasizes the importance of studying host-pathogen relationships in the appropriate species as extrapolation from other animal models may be incorrect and confounded by differences in the host responses.

Hyperglycemia Impairs Neutrophil-Mediated Bacterial Clearance in Mice Infected with the Lyme Disease Pathogen

Insulin-insufficient type 1 diabetes is associated with attenuated bactericidal function of neutrophils, which are key mediators of innate immune responses to microbes as well as pathological inflammatory processes. Neutrophils are central to immune responses to the Lyme pathogen Borrelia burgdorferi. The effect of hyperglycemia on host susceptibility to and outcomes of B. burgdorferi infection has not been examined. The present study investigated the impact of sustained obesity-independent hyperglycemia in mice on bacterial clearance, inflammatory pathology and neutrophil responses to B. burgdorferi. Hyperglycemia was associated with reduced arthritis incidence but more widespread tissue colonization and reduced clearance of bacterial DNA in multiple tissues including brain, heart, liver, lung and knee joint. B. burgdorferi uptake and killing were impaired in neutrophils isolated from hyperglycemic mice. Thus, attenuated neutrophil function in insulin-insufficient hyperglycemia was associated with reduced B. burgdorferi clearance in target organs. These data suggest that investigating the effects of comorbid conditions such as diabetes on outcomes of B. burgdorferi infections in humans may be warranted.

The Impact of Non-Enzymatic Reactions and Enzyme Promiscuity on Cellular Metabolism during (Oxidative) Stress Conditions

Cellular metabolism assembles in a structurally highly conserved, but functionally dynamic system, known as the metabolic network. This network involves highly active, enzyme-catalyzed metabolic pathways that provide the building blocks for cell growth. In parallel, however, chemical reactivity of metabolites and unspecific enzyme function give rise to a number of side products that are not part of canonical metabolic pathways. It is increasingly acknowledged that these molecules are important for the evolution of metabolism, affect metabolic efficiency, and that they play a potential role in human disease—age-related disorders and cancer in particular. In this review we discuss the impact of oxidative and other cellular stressors on the formation of metabolic side products, which originate as a consequence of: (i) chemical reactivity or modification of regular metabolites; (ii) through modifications in substrate specificity of damaged enzymes; and (iii) through altered metabolic flux that protects cells in stress conditions. In particular, oxidative and heat stress conditions are causative of metabolite and enzymatic damage and thus promote the non-canonical metabolic activity of the cells through an increased repertoire of side products. On the basis of selected examples, we discuss the consequences of non-canonical metabolic reactivity on evolution, function and repair of the metabolic network.

Expression of stress-related proteins in Sediminibacterium sp. growing under planktonic conditions

Aggregation is a common trait of bacteria in natural and engineered biological systems. Microbial aggregates, such as flocs, granules, and biofilms, are spatially heterogeneous environments. It is generally observed that by growing under aggregated conditions bacteria respond and adapt to environmental stress better than free-swimming bacteria of the same species. We performed a proteomic analysis of a strain of Sediminibacterium, isolated from activated sludge, which grew planktonically in diluted culture media and in an aggregated form in media containing a high concentration of organic substrate. Auto-aggregation was also observed in the presence of pyruvate in dilute media. Expression of a number of stress-related proteins significantly increased under planktonic growth in comparison to aggregate growth. The upregulated proteins, identified by MALDI-TOF mass spectrometry, were two isoforms of a protein belonging to the universal stress family (UspA), a thioredoxin-disulfide reductase, the Campylobacter jejuni orthologue transcriptional regulator (Cj1172c), and the CocE/NonD hydrolase. We conclude that Sediminibaterium sp. C3 growth is stressed under planktonic conditions and that aggregation induced by pyruvate protects the bacteria against oxidative stress.

Effects of apocynin, an NADPH oxidase inhibitor, on levels of ADMA, MPO, iNOS and TLR4 induced by myocardial ischemia reperfusion

PURPOSE

In this study, the effects of apocynin, an NADPH oxidase inhibitor, on the levels of inducible nitric oxide synthase (iNOS) and the toll-like receptor 4 (TLR4), which are inflammatory mediators in myocardial ischemia-reperfusion (MIR) injury, and myeloperoxidase (MPO), which is the indicator of neutrophil infiltration and the endogenous nitric oxide synthase inhibitor asymmetric dimethyl arginine (ADMA) increasing with oxidative stress were investigated.

METHODS

MIR injury was accomplished by the application of occlusion for 30 minutes and reperfusion for 120 minutes in the left anterior descending artery (LAD). In the study, 21 Sprague-Dawley male rats were divided into three groups: a sham group (n = 7); a MIR group (n = 7); and a MIR + apocynin treatment group (n = 7, before the procedure, an intraperitoneal administration of 10 mg/kg of apocynin for 15 days). After reperfusion, iNOS, TLR4, MPO and ADMA levels in myocardial tissue were measured by ELISA.

RESULTS

While myocardial TLR4, MPO and ADMA levels increased in the MIR group, these parameters were found to be decreased significantly in the group treated with apocynin. Although iNOS levels showed an increase in the MIR group compared to the sham group and a reduction in the MIR+apocynin group, there was no statistically significant difference between the groups.

DISCUSSION

In our study, the effect of the treatment of apocynin in MIR on ADMA, MPO, iNOS and TLR4 levels in myocardial tissue was shown for the first time. It is thought that apocynin treatment may show a protective effect in MIR injury by affecting oxidative stress (ADMA) and inflammatory parameters (iNOS, MPO).