A Comprehensive Assessment of the Genetic Determinants in Salmonella Typhimurium for Resistance to Hydrogen Peroxide Using Proteogenomics

Adaptive evolution of Salmonella Typhimurium LT2 exposed to carvacrol lacks a uniform pattern

Emergence of genetic variants with increased resistance/tolerance to natural antimicrobials, such as essential oils, has been previously evidenced; however, it is unknown whether mutagenesis follows a general or a specific pattern. For this purpose, we carried out four adaptive laboratory evolutions (ALE) in parallel of Salmonella enterica Typhimurium with carvacrol. After 10 evolution steps, we selected and characterized one colony from each lineage (SeCarA, SeCarB, SeCarC, and SeCarD). Phenotypic characterization of the four evolved strains revealed enhanced survival to lethal treatments; two of them (SeCarA and SeCarB) showed an increase of minimum inhibitory concentration of carvacrol and a better growth fitness in the presence of carvacrol compared to wild-type strain. Whole genome sequencing revealed 10 mutations, of which four (rrsH, sseG, wbaV, and flhA) were present in more than one strain, whereas six (nirC, fliH, lon, rob, upstream yfhP, and upstream argR) were unique to individual strains. Single-mutation genetic constructs in SeWT confirmed lon and rob as responsible for the increased resistance to carvacrol as well as to antibiotics (ampicillin, ciprofloxacin, chloramphenicol, nalidixic acid, rifampicin, tetracycline, and trimethoprim). wbaV played an important role in increased tolerance against carvacrol and chloramphenicol, and flhA in cross-tolerance to heat treatments. As a conclusion, no common phenotypical or genotypical pattern was observed in the isolated resistant variants of Salmonella Typhimurium emerged under carvacrol stress. Furthermore, the demonstration of cross-resistance against heat and antibiotics exhibited by resistant variants raises concerns regarding food safety. KEY POINTS: • Stable resistant variants of Salmonella Typhimurium emerged under carvacrol stress • No common pattern of mutagenesis after cyclic exposures to carvacrol was observed • Resistant variants to carvacrol showed cross-resistance to heat and to antibiotics.

Integrative DNA methylome and transcriptome analysis reveals DNA adenine methylation is involved in Salmonella enterica Typhimurium response to oxidative stress

IMPORTANCE

The intracellular pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium) comes across a wide variety of stresses from entry to dissemination, such as reactive oxygen species. To adapt itself to oxidative stress, Salmonella must adopt various and complex strategies. In this study, we revealed that DNA adenine methyltransferase was essential for S. Typhimurium to survive in hydrogen peroxide. We then screened out oxidative stress-responsive genes that were potentially regulated by DNA methylation in S. Typhimurium. Our results show that the DNA methylome is highly stable throughout the genome, and the coupled change of m6A GATC with gene expression is identified in only a few positions, which suggests the complexity of the DNA methylation and gene expression regulation networks. The results may shed light on our understanding of m6A-mediated gene expression regulation in bacteria.

Novel method to recover Salmonella enterica cells for Tn-Seq approaches from lettuce leaves and agricultural environments using combination of sonication, filtration, and dialysis membrane

Salmonella enterica in agricultural environments has become an important concern, due to its potential transmission to humans and the associated public health risks. To identify genes contributing to Salmonella adaptation to such environments, transposon sequencing has been used in recent years. However, isolating Salmonella from atypical hosts, such as plant leaves, can pose technical challenges due to low bacterial content and the difficulty to separate an adequate number of bacteria from host tissues. In this study, we describe a modified methodology using a combination of sonication and filtration to recover S. enterica cells from lettuce leaves. We successfully recovered over a total of 3.5 × 106Salmonella cells in each biological replicate from two six-week old lettuce leaves, 7 days after infiltration with a Salmonella suspension of 5 × 107 colony forming units (CFU)/mL. Moreover, we have developed a dialysis membrane system as an alternative method for recovering bacteria from culture medium, mimicking a natural environment. Inoculating 107 CFU/mL of Salmonella into the media based on plant (lettuce and tomato) leaf and diluvial sand soil, a final concentration of 109.5 and 108.5 CFU/mL was obtained, respectively. One millilitre of the bacterial suspension after 24 h incubation at 28 °C using 60 rpm agitation was pelleted, corresponding to 109.5 and 108.5 cells from leaf- or soil-based media. The recovered bacterial population, from both lettuce leaves and environment-mimicking media, can adequately cover a presumptive library density of 106 mutants. In conclusion, this protocol provides an effective method to recover a Salmonella transposon sequencing library from in planta and in vitro systems. We expect this novel technique to foster the study of Salmonella in atypical hosts and environments, as well as other comparable scenarios.

Genome-wide characterization of Salmonella Typhimurium genes required for the fitness under iron restriction

Background

Iron is a crucial element for bacterial survival and virulence. During Salmonella infection, the host utilizes a variety of mechanisms to starve the pathogen from iron. However, Salmonella activates distinctive defense mechanisms to acquire iron and survive in iron-restricted host environments. Yet, the comprehensive set of the conditionally essential genes that underpin Salmonella survival under iron-restricted niches has not been fully explored.

Results

Here, we employed transposon sequencing (Tn-seq) method for high-resolution elucidation of the genes in Salmonella Typhimurium (S. Typhimurium) 14028S strain required for the growth under the in vitro conditions with four different levels of iron restriction achieved by iron chelator 2,2′-dipyridyl (Dip): mild (100 and 150 μM), moderate (250 μM) and severe iron restriction (400 μM). We found that the fitness of the mutants reduced significantly for 28 genes, suggesting the importance of these genes for the growth under iron restriction. These genes include sufABCDSE, iron transport fepD, siderophore tonB, sigma factor E ropE, phosphate transport pstAB, and zinc exporter zntA. The siderophore gene tonB was required in mild and moderate iron-restricted conditions, but it became dispensable in severe iron-restricted conditions. Remarkably, rpoE was required in moderate and severe iron restrictions, leading to complete attenuation of the mutant under these conditions. We also identified 30 genes for which the deletion of the genes resulted in increased fitness under iron-restricted conditions.

Conclusions

The findings broaden our knowledge of how S. Typhimurium survives in iron-deficient environments, which could be utilized for the development of new therapeutic strategies targeting the pathways vital for iron metabolism, trafficking, and scavenging.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12863-022-01069-3.

Gene essentiality profiling reveals a novel determinant of stresses preventing protein aggregation in Salmonella

Adaptation to various stresses during infection is important for Salmonella Typhimurium virulence, while the fitness determinants under infection-relevant stress conditions remain unknown. Here, we simulated conditions Salmonella encountered within the host or in the environment by 15 individual stresses as well as two model cell lines (epithelium and macrophage) to decipher the genes and pathways required for fitness. By high-resolution Tn-seq analysis, a total of 1242 genes were identified as essential for fitness under at least one stress condition. The comparative analysis of fitness determinants in 17 stress conditions indicated the essentiality of genes varied in different mimicking host niches. A total of 12 genes were identified as fitness determinants in all stress conditions, including recB, recC, and xseA (encode three exonuclease subunits necessary for DNA recombination repair) and a novel essential fitness gene yheM. YheM is a putative sulfurtransferase subunit that is responsible for tRNA modification, and our results showed that Salmonella lacking yheM accumulated more aggregates of endogenous protein than wild-type. Moreover, we established a scoring scheme for sRNA essentiality analysis and found STnc2080 of unknown function was essential for resistance to LL-37. In summary, we systematically dissected Salmonella gene essentiality profiling and demonstrated the general and specific adaptive requirements in infection-relevant niches. Our data not only provide valuable insights on how Salmonella responds to environmental stresses during infections but also highlight the potential clinical application of fitness determinants in vaccine development.

Transposon-Directed Insertion-Site Sequencing Reveals Glycolysis Gene gpmA as Part of the H2O2 Defense Mechanisms in Escherichia coli

Hydrogen peroxide (H₂O₂) is a common effector of defense mechanisms against pathogenic infections. However, bacterial factors involved in H₂O₂ tolerance remain unclear. Here we used transposon-directed insertion-site sequencing (TraDIS), a technique allowing the screening of the whole genome, to identify genes implicated in H₂O₂ tolerance in Escherichia coli. Our TraDIS analysis identified 10 mutants with fitness defect upon H₂O₂ exposure, among which previously H₂O₂-associated genes (oxyR, dps, dksA, rpoS, hfq and polA) and other genes with no known association with H₂O₂ tolerance in E. coli (corA, rbsR, nhaA and gpmA). This is the first description of the impact of gpmA, a gene involved in glycolysis, on the susceptibility of E. coli to H₂O₂. Indeed, confirmatory experiments showed that the deletion of gpmA led to a specific hypersensitivity to H₂O₂ comparable to the deletion of the major H₂O₂ scavenger gene katG. This hypersensitivity was not due to an alteration of catalase function and was independent of the carbon source or the presence of oxygen. Transcription of gpmA was upregulated under H₂O₂ exposure, highlighting its role under oxidative stress. In summary, our TraDIS approach identified gpmA as a member of the oxidative stress defense mechanism in E. coli.

Genome-Wide Identification of Pseudomonas aeruginosa Genes Important for Desiccation Tolerance on Inanimate Surfaces

Pseudomonas aeruginosa is an opportunistic pathogen prevalent in the environment and in health care settings. Transmission in the health care setting occurs through human-human interactions and/or contact with contaminated surfaces. Moist surfaces such as respirators, sink and tub drains, and even disinfectants can serve as reservoirs. Dry surfaces such as plastic and stainless steel could also serve as a reservoir but would necessitate some degree of tolerance to desiccation. Using an assay to measure P. aeruginosa tolerance to desiccation on plastic and stainless-steel surfaces, we found that only 0.05 to 0.1% of the desiccated cells could be recovered 24 h postdesiccation. We took advantage of the strong selection imposed by desiccation to identify genes important for tolerance using Tn-seq. A highly saturated Tn-seq library was desiccated on plastic and stainless-steel surfaces. NexGen sequencing of the recovered cells identified 97 genes important for survival. Comparing cells desiccated under low- and high-nutrient conditions allowed for differentiation of genes important for desiccation tolerance. The 53 genes identified in the latter analysis are involved in maintenance of cell envelope integrity, purine and pyrimidine biosynthesis, tricarboxylic acid (TCA) cycle, and the hydrolysis of misfolded proteins. The Tn-seq findings were validated by competition experiments with wild-type (WT) cells and select Tn insertion mutants. Mutants lacking carB and surA demonstrated the largest fitness defects, indicating that pyrimidine biosynthesis and outer membrane integrity are essential for desiccation tolerance. Increased understanding of desiccation tolerance could provide insight into approaches to control environmental reservoirs of P. aeruginosa.

IMPORTANCE Health care-associated infections (HAIs) caused by Pseudomonas aeruginosa result in significant morbidity and mortality and are a significant economic burden. Moist environments that promote biofilm formation are an important reservoir for P. aeruginosa. Dry environments may also serve as a reservoir but would require some degree of desiccation tolerance. Here, we took a genome-wide approach to identify genes important for desiccation tolerance on plastic and stainless-steel surfaces. Genes involved in assembly of outer membrane proteins and pyrimidine biosynthesis were particularly important. Strains lacking these functions were unable to tolerate surface desiccation. These findings suggest that inhibitors of these pathways could be used to prevent P. aeruginosa survival on dry surfaces.

Coordinated interaction between Lon protease and catalase-peroxidase regulates virulence and oxidative stress management during Salmonellosis

This study investigates the interplay between Lon protease and catalase-peroxidase (KatG) in relation to virulence modulation and the response to oxidative stress in Salmonella Typhimurium (ST). Proteomic comparison of ST wild-type and lon deletion mutant led to the recognition of a highly expressed KatG protein product among five other protein candidates that were significantly affected by lon deletion. By employing a bacterium two-hybrid assay (B2H), we demonstrated that the catalytic domain of Lon protease potentially interacts with the KatG protein that leads to proteolytic cleavage. Assessment of virulence gene expression in single and double lon and katG mutants revealed katG to be a potential positive modulator of both Salmonella pathogenicity Island-1 (SPI-1) and -2, while lon significantly affected SPI-1 genes. ST double deletion mutant, ∆lon∆katG was more susceptible to survival defects within macrophage-like cells and exhibited meager colonization of the mouse spleen compared to the single deletion mutants. The findings reveal a previously unknown function of Lon and KatG interaction in Salmonella virulence. Taken together, our experiments demonstrate the importance of Lon and KatG to cope with oxidative stress, for intracellular survival and in vivo virulence of Salmonella.

Genetic Determinants in Salmonella enterica Serotype Typhimurium Required for Overcoming In Vitro Stressors in the Mimicking Host Environment

Salmonella enterica serotype Typhimurium, a nontyphoidal Salmonella (NTS), results in a range of enteric diseases, representing a major disease burden worldwide. There is still a significant portion of Salmonella genes whose mechanistic basis to overcome host innate defense mechanisms largely remains unknown. Here, we have applied transposon insertion sequencing (Tn-seq) method to unveil the genetic factors required for the growth or survival of S. Typhimurium under various host stressors simulated in vitro. A highly saturating Tn5 library of S. Typhimurium 14028s was subjected to selection during growth in the presence of short-chain fatty acid (100 mM propionate), osmotic stress (3% NaCl), or oxidative stress (1 mM H2O2) or survival in extreme acidic pH (30 min in pH 3) or starvation (12 days in 1× phosphate-buffered saline [PBS]). We have identified a total of 339 conditionally essential genes (CEGs) required to overcome at least one of these conditions mimicking host insults. Interestingly, all eight genes encoding FoF1-ATP synthase subunit proteins were required for fitness in all five stresses. Intriguingly, a total of 88 genes in Salmonella pathogenicity islands (SPI), including SPI-1, SPI-2, SPI-3, SPI-5, SPI-6, and SPI-11, are also required for fitness under the in vitro conditions. Additionally, by comparative analysis of the genes identified in this study and the genes previously shown to be required for in vivo fitness, we identified novel genes (marBCT, envF, barA, hscA, rfaQ, rfbI, and the genes encoding putative proteins STM14_1138, STM14_3334, STM14_4825, and STM_5184) that have compelling potential for the development of vaccines and antibacterial drugs to curb Salmonella infection. IMPORTANCE Salmonella enterica serotype Typhimurium is a major human bacterial pathogen that enters the food chain through meat animals asymptomatically carrying this pathogen. Despite the rich genome sequence data, a significant portion of Salmonella genes remain to be characterized for their potential contributions to virulence. In this study, we used transposon insertion sequencing (Tn-seq) to elucidate the genetic factors required for growth or survival under various host stressors, including short-chain fatty acids, osmotic stress, oxidative stress, extreme acid, and starvation. Among the total of 339 conditionally essential genes (CEGs) that are required under at least one of these five stress conditions were 221 previously known virulence genes required for in vivo fitness during infection in at least one of four animal species, including mice, chickens, pigs, and cattle. This comprehensive map of virulence phenotype-genotype in S. Typhimurium provides a roadmap for further interrogation of the biological functions encoded by the genome of this important human pathogen to survive in hostile host environments.

Sodium butyrate modulates chicken macrophage proteins essential for Salmonella Enteritidis invasion

Salmonella Enteritidis is an intracellular foodborne pathogen that has developed multiple mechanisms to alter poultry intestinal physiology and infect the gut. Short chain fatty acid butyrate is derived from microbiota metabolic activities, and it maintains gut homeostasis. There is limited understanding on the interaction between S. Enteritidis infection, butyrate, and host intestinal response. To fill this knowledge gap, chicken macrophages (also known as HTC cells) were infected with S. Enteritidis, treated with sodium butyrate, and proteomic analysis was performed. A growth curve assay was conducted to determine sub-inhibitory concentration (SIC, concentration that do not affect bacterial growth compared to control) of sodium butyrate against S. Enteritidis. HTC cells were infected with S. Enteritidis in the presence and absence of SIC of sodium butyrate. The proteins were extracted and analyzed by tandem mass spectrometry. Our results showed that the SIC was 45 mM. Notably, S. Enteritidis-infected HTC cells upregulated macrophage proteins involved in ATP synthesis through oxidative phosphorylation such as ATP synthase subunit alpha (ATP5A1), ATP synthase subunit d, mitochondrial (ATP5PD) and cellular apoptosis such as Cytochrome-c (CYC). Furthermore, sodium butyrate influenced S. Enteritidis-infected HTC cells by reducing the expression of macrophage proteins mediating actin cytoskeletal rearrangements such as WD repeat-containing protein-1 (WDR1), Alpha actinin-1 (ACTN1), Vinculin (VCL) and Protein disulfide isomerase (P4HB) and intracellular S. Enteritidis growth and replication such as V-type proton ATPase catalytic subunit A (ATPV1A). Interestingly, sodium butyrate increased the expression of infected HTC cell protein involving in bacterial killing such as Vimentin (VIM). In conclusion, sodium butyrate modulates the expression of HTC cell proteins essential for S. Enteritidis invasion.

Turgor-dependent and coronin-mediated F-actin dynamics drive septin disc-to-ring remodeling in the blast fungus Magnaporthe oryzae

The fungus Magnaporthe oryzae uses a specialized pressure-generating infection cell called an appressorium to break into rice leaves and initiate disease. Appressorium functionality is dependent on the formation of a cortical septin ring during its morphogenesis, but precisely how this structure assembles is unclear. Here, we show that F-actin rings are recruited to the circumference of incipient septin disc-like structures in a pressure-dependent manner, and that this is necessary for their contraction and remodeling into rings. We demonstrate that the structural integrity of these incipient septin discs requires both an intact F-actin and microtubule cytoskeleton and provide fundamental new insight into their functional organization within the appressorium. Lastly, using proximity-dependent labeling, we identify the actin modulator coronin as a septin-proximal protein and show that F-actin-mediated septin disc-to-ring remodeling is perturbed in the genetic absence of coronin. Taken together, our findings provide new insight into the dynamic remodeling of infection-specific higher-order septin structures in a globally significant fungal plant pathogen.

Genetic Variants and Phenotypic Characteristics of Salmonella Typhimurium-Resistant Mutants after Exposure to Carvacrol

The emergence of antimicrobial resistance has raised questions about the safety of essential oils and their individual constituents as food preservatives and as disinfection agents. Further research is required to understand how and under what conditions stable genotypic resistance might occur in food pathogens. Evolution experiments on Salmonella Typhimurium cyclically exposed to sublethal and lethal doses of carvacrol permitted the isolation of SeSCar and SeLCar strains, respectively. Both evolved strains showed a significant increase in carvacrol resistance, assessed by minimum inhibitory and bactericidal concentrations, the study of growth kinetics in the presence of carvacrol, and the evaluation of survival under lethal conditions. Moreover, antibiotic susceptibility tests revealed a development of SeLCar resistance to a wide range of antibiotics. Whole genome sequencing allowed the identification of single nucleotide variations in transcriptional regulators of oxidative stress-response: yfhP in SeSCar and soxR in SeLCar, which could be responsible for the increased resistance by improving the response to carvacrol and preventing its accumulation inside the cell. This study demonstrates the emergence of S. Typhimurium-resistant mutants against carvacrol, which might pose a risk to food safety and should therefore be considered in the design of food preservation strategies, or of cleaning and disinfection treatments.

The Arabidopsis Proteins AtNHR2A and AtNHR2B Are Multi-Functional Proteins Integrating Plant Immunity With Other Biological Processes

AtNHR2A (Arabidopsis thaliana nonhost resistance 2A) and AtNHR2B (Arabidopsis thaliana nonhost resistance 2B) are two proteins that participate in nonhost resistance, a broad-spectrum mechanism of plant immunity that protects plants against the majority of potential pathogens. AtNHR2A and AtNHR2B are localized to the cytoplasm, chloroplasts, and other subcellular compartments of unknown identity. The multiple localizations of AtNHR2A and AtNHR2B suggest that these two proteins are highly dynamic and versatile, likely participating in multiple biological processes. In spite of their importance, the specific functions of AtNHR2A and AtNHR2B have not been elucidated. Thus, to aid in the functional characterization of these two proteins and identify the biological processes in which these proteins operate, we used immunoprecipitation coupled with mass spectrometry (IP-MS) to identify proteins interacting with AtNHR2A and AtNHR2B and to generate their interactome network. Further validation of three of the identified proteins provided new insights into specific pathways and processes related to plant immunity where AtNHR2A and AtNHR2B participate. Moreover, the comprehensive analysis of the AtNHR2A- and AtNHR2B-interacting proteins using published empirical information revealed that the functions of AtNHR2A and AtNHR2B are not limited to plant immunity but encompass other biological processes.

An intra-bacterial activity for a T3SS effector

Many Gram-negative bacterial pathogens interact with mammalian cells by using type III secretion systems (T3SS) to inject virulence proteins into host cells. A subset of these injected protein 'effectors' are enzymes that inhibit the function of host proteins by catalyzing the addition of unusual post-translational modifications. The E. coli and Citrobacter rodentium NleB effectors, as well as the Salmonella enterica SseK effectors are glycosyltransferases that modify host protein substrates with N-acetyl glucosamine (GlcNAc) on arginine residues. This post-translational modification disrupts the normal functioning of host immune response proteins. T3SS effectors are thought to be inactive within the bacterium and fold into their active conformations after they are injected, due to the activity of chaperones that keep the effectors in a structural state permissive for secretion. While performing mass spectrometry experiments to identify glycosylation substrates of NleB orthologs, we unexpectedly observed that the bacterial glutathione synthetase (GshB) is glycosylated by NleB on arginine residue R256. NleB-mediated glycosylation of GshB resulted in enhanced GshB activity, leading to an increase in glutathione production, and promoted C. rodentium survival in oxidative stress conditions. These data represent, to our knowledge, the first intra-bacterial activity for a T3SS effector and show that arginine-GlcNAcylation, once thought to be restricted to host cell compartments, also plays an important role in regulating bacterial physiology.

Preparation of Transposon Library and Tn-Seq Amplicon Library for Salmonella Typhimurium

Transposon sequencing (Tn-seq) is a powerful tool for functional genomics of bacteria. Tn-seq combines transposon mutagenesis with next generation sequencing to assess genetic requirements at a genome-wide scale and identify essential and conditionally essential genes. An efficient application of this experimental approach relies on robust protocols for transposon mutagenesis system and Tn-seq amplicon library preparation method. However, the existing approaches for the Tn-seq amplicon library preparation have several shortcomings. Hence, we present a robust, fast, specific, and cost-effective approach for the transposon mutagenesis of Salmonella Typhimurium and Tn-seq amplicon library preparation for Illumina sequencing. Besides S. Typhimurium that was used here for illustration, this protocol can also be used for other bacteria. In particular, the procedure for Tn-seq amplicon library preparation can be broadly applicable to any transposon elements. We delineate comprehensive step-by-step protocols for transposon mutagenesis and Tn-seq amplicon library such that it can be reproduced effortlessly by other researchers.

Iron-dependent essential genes in Salmonella Typhimurium

Background

The molecular mechanisms underlying bacterial cell death due to stresses or bactericidal antibiotics are complex and remain puzzling. Due to the current crisis of antibiotic resistance, development of effective antibiotics is urgently required. Previously, it has been shown that iron is required for effective killing of bacterial cells by numerous bactericidal antibiotics.

Results

We investigated the death or growth inhibition of S. Typhimurium under iron-restricted conditions, following disruption of essential genes, by transposon mutagenesis using transposon sequencing (Tn-seq). Our high-resolution Tn-seq analysis revealed that transposon mutants of S. Typhimurium with insertions in essential genes escaped immediate killing or growth inhibition under iron-restricted conditions for approximately one-third of all previously known essential genes. Based on this result, we classified all essential genes into two categories, iron-dependent essential genes, for which the insertion mutants can grow slowly if iron is restricted, and iron-independent essential genes, for which the mutants become nonviable regardless of iron concentration. The iron-dependency of the iron-dependent essential genes was further validated by the fact that the relative abundance of these essential gene mutants increased further with more severe iron restrictions. Our unexpected observation can be explained well by the common killing mechanisms of bactericidal antibiotics via production of reactive oxygen species (ROS). In this model, iron restriction would inhibit production of ROS, leading to reduced killing activity following blocking of essential gene functions. Interestingly, the targets of most antibiotics currently in use clinically are iron-dependent essential genes.

Conclusions

Our result suggests that targeting iron-independent essential genes may be a better strategy for future antibiotic development, because blocking their essential gene functions would lead to immediate cell death regardless of the iron concentration. This work expands our knowledge on the role of iron to a broad range of essential functions and pathways, providing novel insights for development of more effective antibiotics.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4986-1) contains supplementary material, which is available to authorized users.

Pulmonary Surfactant Promotes Virulence Gene Expression and Biofilm Formation in Klebsiella pneumoniae

The interactions between Klebsiella pneumoniae and the host environment at the site of infection are largely unknown. Pulmonary surfactant serves as an initial point of contact for inhaled bacteria entering the lung and is thought to contain molecular cues that aid colonization and pathogenesis. To gain insight into this ecological transition, we characterized the transcriptional response of K. pneumoniae MGH 78578 to purified pulmonary surfactant. This work revealed changes within the K. pneumoniae transcriptome that likely contribute to host colonization, adaptation, and virulence in vivo Notable transcripts expressed under these conditions include genes involved in capsule synthesis, lipopolysaccharide modification, antibiotic resistance, biofilm formation, and metabolism. In addition, we tested the contributions of other surfactant-induced transcripts to K. pneumoniae survival using engineered isogenic KPPR1 deletion strains in a murine model of acute pneumonia. In these infection studies, we identified the MdtJI polyamine efflux pump and the ProU glycine betaine ABC transporter to be significant mediators of K. pneumoniae survival within the lung and confirmed previous evidence for the importance of de novo leucine synthesis to bacterial survival during infection. Finally, we determined that pulmonary surfactant promoted type 3 fimbria-mediated biofilm formation in K. pneumoniae and identified two surfactant constituents, phosphatidylcholine and cholesterol, that drive this response. This study provides novel insight into the interactions occurring between K. pneumoniae and the host at an important infection site and demonstrates the utility of purified lung surfactant preparations for dissecting host-lung pathogen interactions in vitro.

Iron-dependent reconfiguration of the proteome underlies the intracellular lifestyle of Brucella abortus

Brucella ssp. is a facultative intracellular pathogen that causes brucellosis, a worldwide zoonosis that affects a wide range of mammals including humans. A critical step for the establishment of a successful Brucella infection is its ability to survive within macrophages. To further understand the mechanisms that Brucella utilizes to adapt to an intracellular lifestyle, a differential proteomic study was performed for the identification of intracellular modulated proteins. Our results demonstrated that at 48 hours post-infection Brucella adjusts its metabolism in order to survive intracellularly by modulating central carbon metabolism. Remarkably, low iron concentration is likely the dominant trigger for reprogramming the protein expression profile. Up-regulation of proteins dedicated to reduce the concentration of reactive oxygen species, protein chaperones that prevent misfolding of proteins, and proteases that degrade toxic protein aggregates, suggest that Brucella protects itself from damage likely due to oxidative burst. This proteomic analysis of B. abortus provides novel insights into the mechanisms utilized by Brucella to establish an intracellular persistent infection and will aid in the development of new control strategies and novel targets for antimicrobial therapy.