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Goldberg, J. B.

Publications and source records attributed to Goldberg, J. B..

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The interplay between temperature and growth phase shapes the transcriptional landscape of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a highly versatile bacterium capable of surviving and often thriving in stressful environmental conditions. Here we report the effect of two environmental conditions, temperature and growth phase, on the P. aeruginosa PAO1 transcriptome. As P. aeruginosa is well-known for its growth phase dependent phenotypes and gene regulation, our goal was to determine how temperature altered global gene expression at exponential versus stationary phase and to characterize how growth phase affects thermoregulation. To do this, we grew PAO1 in parallel at 25{degrees}C and 37{degrees}C and sampled the same populations first at exponential phase and then again at stationary phase and assessed gene expression by RNA-sequencing. We found that temperature regulated hundreds of genes at, and unique to, exponential and stationary phase. We also grew PAO1 and an isogenic {Delta}lasR mutant at 25{degrees}C and 37{degrees}C and sampled populations at stationary phase to define LasR-regulated genes at each temperature by RNA-sequencing. LasR regulated most of its target genes similarly at 25{degrees}C and 37{degrees}C, although we identified a subset of genes whose regulation by LasR was affected by temperature. This work provides a comprehensive thermoregulon for PAO1 at two distinct growth phases, as well as growth phase transcriptomics at two temperatures, and expands our understanding of quorum sensing regulation under different environmental conditions that P. aeruginosa encounters. IMPORTANCEPseudomonas aeruginosa is a highly adaptable opportunistic pathogen with a repertoire of mechanisms for surviving in diverse and often challenging environments yet is most often studied at 37{degrees}C as the optimum temperature for growth. To better understand how this bacterium survives in the environment versus the human body, we performed transcriptomics on P. aeruginosa grown at 25{degrees}C and 37{degrees}C. At each temperature, we examined both exponential and stationary phases. We also determined the LasRI quorum sensing regulon at 37{degrees}C compared to 25{degrees}C using a {Delta}lasR mutant, which uncovered a suite of previously unrecognized LasR-regulated genes. Our work provides a comprehensive transcriptomic resource for thermoregulation of P. aeruginosa at two growth phases, as well as growth phase and LasR regulation at two temperatures.

microbiology↗

Loss of O-specific antigen shapes Pseudomonas aeruginosa microbiogeography in murine preclinical pulmonary infection model

Chronic Pseudomonas aeruginosa infections are the hallmark of late-stage lung disease in individuals with cystic fibrosis. During chronic infection P. aeruginosa becomes the dominant bacteria in the airways. Within-host adaptation of P. aeruginosa leads to vast phenotypic and genetic population heterogeneity. In vitro studies show mutations in lipopolysaccharide (LPS) O-specific antigen changes the aggregate formation in P. aeruginosa, however role of these changes in aggregate assembly in vivo is not understood. Using a synthetic CF sputum media and a preclinical murine infection model we assessed how the PAO1 wildtype and O-specific antigen mutants interact with each other, and if P. aeruginosa population heterogeneity affects the colonization of the murine lungs. Our findings suggest that the presence of variants lacking O-specific antigen does not impact the population fitness and size in both in vitro and in vivo, however it can influence the aggregate volume in vivo.

microbiology↗

LasR regulates protease IV expression at suboptimal growth temperatures in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a highly versatile bacterium capable of surviving and often thriving in stressful environmental conditions. Here we report the effect of two environmental conditions, temperature and growth phase, on the P. aeruginosa PAO1 transcriptome. As P. aeruginosa is well-known for its growth phase dependent phenotypes and gene regulation, our goal was to determine how temperature altered global gene expression at exponential versus stationary phase and to characterize how growth phase affects thermoregulation. To do this, we grew PAO1 in parallel at 25{degrees}C and 37{degrees}C and sampled the same populations first at exponential phase and then again at stationary phase and assessed gene expression by RNA-sequencing. We found that temperature regulated hundreds of genes at, and unique to, exponential and stationary phase. We also grew PAO1 and an isogenic {Delta}lasR mutant at 25{degrees}C and 37{degrees}C and sampled populations at stationary phase to define LasR-regulated genes at each temperature by RNA-sequencing. LasR regulated most of its target genes similarly at 25{degrees}C and 37{degrees}C, although we identified a subset of genes whose regulation by LasR was affected by temperature. This work provides a comprehensive thermoregulon for PAO1 at two distinct growth phases, as well as growth phase transcriptomics at two temperatures, and expands our understanding of quorum sensing regulation under different environmental conditions that P. aeruginosa encounters. IMPORTANCEPseudomonas aeruginosa is a highly adaptable opportunistic pathogen with a repertoire of mechanisms for surviving in diverse and often challenging environments yet is most often studied at 37{degrees}C as the optimum temperature for growth. To better understand how this bacterium survives in the environment versus the human body, we performed transcriptomics on P. aeruginosa grown at 25{degrees}C and 37{degrees}C. At each temperature, we examined both exponential and stationary phases. We also determined the LasRI quorum sensing regulon at 37{degrees}C compared to 25{degrees}C using a {Delta}lasR mutant, which uncovered a suite of previously unrecognized LasR-regulated genes. Our work provides a comprehensive transcriptomic resource for thermoregulation of P. aeruginosa at two growth phases, as well as growth phase and LasR regulation at two temperatures.

microbiology↗

Serotype switching in Pseudomonas aeruginosa ST111 enhances adhesion and virulence

Evolution of the highly successful and multidrug resistant clone ST111 in Pseudomonas aeruginosa involves serotype switching from O-antigen O4 to O12. How expression of a different O-antigen serotype alters pathogen physiology to enable global dissemination of this high-risk clone-type is not understood. Here, we engineered isogenic laboratory and clinical P. aeruginosa strains that express the different O-antigen gene clusters to assess the correlation of structural differences of O4 and O12 O-antigens to pathogen-relevant phenotypic traits. We show that serotype O12 is associated with enhanced adhesion, type IV pili dependent twitching motility, and tolerance to host defense molecules and serum. Moreover, we find that serotype O4 is less virulent compared to O12 in an acute murine pneumonia infection in terms of both colonization and survival rate. Finally, we find that these O-antigen effects may be explained by specific biophysical properties of the serotype repeat unit found in O4 and O12, and by differences in membrane stability between O4 and O12 expressing cells. The results demonstrate that differences in O-antigen sugar composition can directly affect P. aeruginosa pathogenicity traits, and provide a better understanding of the potential selective advantages that underlie serotype switching and emergence of serotype O12 ST111.

microbiology↗

Monoclonal antibodies derived from B cells in subjects with cystic fibrosis reduce Pseudomonas aeruginosa burden in mice

Pseudomonas aeruginosa (PA) is an opportunistic, frequently multidrug-resistant pathogen that can cause severe infections in hospitalized patients. Antibodies against the PA virulence factor, PcrV, protect from death and disease in a variety of animal models. However, clinical trials of PcrV-binding antibody-based products have thus far failed to demonstrate benefit. Prior candidates were derivations of antibodies identified using protein-immunized animal systems and required extensive engineering to optimize binding and/or reduce immunogenicity. Of note, PA infections are common in people with cystic fibrosis (pwCF), who are generally believed to mount normal adaptive immune responses. Here we utilized a tetramer reagent to detect and isolate PcrV-specific B cells in pwCF and, via single-cell sorting and paired-chain sequencing, identified the B cell receptor (BCR) variable region sequences that confer PcrV-specificity. We derived multiple high affinity anti-PcrV monoclonal antibodies (mAbs) from PcrV-specific B cells across 3 donors, including mAbs that exhibit potent anti-PA activity in a murine pneumonia model. This robust strategy for mAb discovery expands what is known about PA-specific B cells in pwCF and yields novel mAbs with potential for future clinical use.

immunology↗

De novo mutations mediate phenotypic switching in an opportunistic human lung pathogen

Bacteria evolving within human hosts encounter selective tradeoffs that render mutations adaptive in one context and deleterious in another. Here, we report that the cystic fibrosis-associated pathogen Burkholderia dolosa overcomes in-human selective tradeoffs by acquiring successive point mutations that alternate phenotypes. We sequenced the whole genomes of 931 respiratory isolates from two recently infected patients and an epidemiologically-linked, chronically-infected patient. These isolates are contextualized using 112 historical genomes from the same outbreak strain. Within both newly infected patients, diverse parallel mutations that disrupt O-antigen expression quickly arose, comprising 29% and 63% of their B. dolosa communities by 3 years. The selection for loss of O-antigen starkly contrasts with our previous observation of parallel O-antigen-restoring mutations after many years of chronic infection in the historical outbreak. Experimental characterization revealed that O-antigen loss increases uptake in immune cells while decreasing competitiveness in the mouse lung. We propose that the balance of these pressures, and thus whether O-antigen expression is advantageous, depends on tissue localization and infection duration. These results suggest that mutation-driven alternation during infection may be more frequent than appreciated and is underestimated without dense temporal sampling.

microbiology↗

Experimentally Evolved Staphylococcus aureus Survives in the Presence of Pseudomonas aeruginosa by Acquiring Mutations in the Amino Acid Transporter, GltT

Staphylococcus aureus and Pseudomonas aeruginosa are the most common bacterial pathogens isolated from cystic fibrosis (CF) related lung infections. When both of these opportunistic pathogens are found in a coinfection, CF patients tend to have higher rates of pulmonary exacerbations and experience a more rapid decrease in lung function. When cultured together under standard laboratory conditions, it is often observed that P. aeruginosa effectively inhibits S. aureus growth. Previous work from our group revealed that S. aureus from CF infections have isolate-specific survival capabilities when cocultured with P. aeruginosa. In this study, we designed a serial transfer evolution experiment to identify mutations that allow S. aureus to adapt to the presence of P. aeruginosa. Using S. aureus USA300 JE2 as our ancestral strain, populations of S. aureus were repeatedly cocultured with fresh P. aeruginosa strain, PAO1. After 8 coculture periods, S. aureus populations that survived better in the presence of PAO1 were observed. We found two independent mutations in the highly conserved S. aureus aspartate transporter, gltT, that were unique to evolved P. aeruginosa-tolerant isolates. Subsequent phenotypic testing demonstrated that gltT mutants have reduced uptake of glutamate and outcompete wild-type S. aureus when glutamate is absent from chemically-defined media. These findings together demonstrate that the presence of P. aeruginosa exerts selective pressure on S. aureus to alter its uptake and metabolism of key amino acids when the two bacteria are cultured together. ImportanceStaphylococcus aureus and Pseudomonas aeruginosa are the two most common bacterial pathogens that infect people with the genetic disease, cystic fibrosis (CF). They are often found together in CF-associated polymicrobial infections that are associated with worse patient prognosis. Understanding how these very different opportunistic pathogens influence each other in a shared environment is pertinent to improving the treatment of polymicrobial infections. While much attention has been brought to the interspecific interactions between S. aureus and P. aeruginosa, few studies have used experimental evolution methods to identify determinants of their competition and coexistence. Here, we use a serial transfer experimental evolution approach and identified a single genetic change associated with improved survival of S. aureus in the presence of P. aeruginosa. Our findings implicate metabolism of shared resources as an important factor in S. aureuss ability to survive in the presence of P. aeruginosa.

microbiology↗

Efficacy of a Pseudomonas aeruginosa Serogroup O9 Vaccine

There are currently no approved vaccines against the opportunistic pathogen Pseudomonas aeruginosa. Among vaccine targets, the lipopolysaccharide (LPS) O antigen of P. aeruginosa is the most immunodominant protective candidate. There are twenty different O antigens composed of different repeat sugars structures conferring serogroup specificity, and ten are found most frequently in infection. Thus, one approach to combat infection by P. aeruginosa could be to generate immunity with a vaccine cocktail that includes all these serogroups. Serogroup O9 is one of the ten serogroups commonly found in infection, but it has never been developed into a vaccine, likely due, in part, to the acid labile nature of the O9 polysaccharide. Our laboratory has previously shown that intranasal administration of an attenuated Salmonella strain expressing the P. aeruginosa serogroup O11 LPS O antigen was effective in clearing and preventing mortality in mice following intranasal challenge with serogroup O11 P. aeruginosa. Consequently, we set out to develop a P. aeruginosa serogroup O9 vaccine using a similar approach. Here we show that Salmonella expressing serogroup O9 triggered an antibody-mediated immune response following intranasal administration to mice and that it conferred protection from P. aeruginosa serogroup O9 in a murine model of acute pneumonia.

microbiology↗

The Type VI Secretion System of the Emerging Pathogen Stenotrophomonas maltophilia has Antibacterial Properties

Antagonistic behaviors between bacterial cells can have profound effects on microbial populations and disease outcomes. Polymicrobial interactions may be mediated by contact-dependent proteins with antibacterial properties. The Type VI Secretion System (T6SS) is a macromolecular weapon used by Gram-negative bacteria to translocate proteins into adjacent cells. The T6SS is used by pathogens to escape immune cells, eliminate commensal bacteria, and facilitate infection. Stenotrophomonas maltophilia is a Gram-negative opportunistic pathogen that causes a wide range of infections in immunocompromised patients and infects the lungs of patients with cystic fibrosis. Infections with the bacterium can be deadly and are challenging to treat because many isolates are multidrug-resistant. We found that globally dispersed S. maltophilia clinical and environmental strains possess T6SS genes. We demonstrate that the T6SS of an S. maltophilia patient isolate is active and can eliminate other bacteria. Furthermore, we provide evidence that the T6SS contributes to the competitive fitness of S. maltophilia against a co-infecting Pseudomonas aeruginosa isolate, and that the T6SS alters the cellular organization of S. maltophilia and P. aeruginosa co-cultures. This study expands our knowledge of the mechanisms employed by S. maltophilia to secrete antibacterial proteins and compete against other bacteria. IMPORTANCEInfections with the opportunistic pathogen Stenotrophomonas maltophilia can be fatal for immunocompromised patients. The mechanisms used by the bacterium to compete against other prokaryotes are not well understood. We found that the T6SS allows S. maltophilia to eliminate other bacteria and contributes to the competitive fitness against a co-infecting isolate. The presence of T6SS genes in isolates across the globe highlights the importance of this apparatus as a weapon in the antibacterial arsenal of S. maltophilia. The T6SS may confer survival advantages to S. maltophilia isolates in polymicrobial communities in both environmental settings and during infections.

microbiology↗

The PqsE active site as a target for small molecule antimicrobial agents against Pseudomonas aeruginosa

The opportunistic pathogen Pseudomonas aeruginosa causes antibiotic resistant, nosocomial infections in immuno-compromised individuals, and is a high priority for antimicrobial development. Key to pathogenicity in P. aeruginosa are biofilm formation and virulence factor production. Both traits are controlled by the cell-to-cell communication process called quorum sensing (QS). QS involves the synthesis, release, and population-wide detection of signal molecules called autoinducers. We previously reported that activity of the RhlR QS transcription factor depends on a protein-protein interaction with the hydrolase, PqsE, and PqsE catalytic activity is dispensable for this interaction. Nonetheless, the PqsE-RhlR interaction could be disrupted by substitution of an active site glutamate residue with tryptophan (PqsE(E182W)). Here, we show that disruption of the PqsE-RhlR interaction via either the E182W change or alteration of PqsE surface residues that are essential for the interaction with RhlR, attenuates P. aeruginosa infection in a murine host. We use crystallography to characterize the conformational changes induced by the PqsE(E182W) substitution to define the mechanism underlying disruption of the PqsE-RhlR interaction. A loop rearrangement that repositions the E280 residue in PqsE(E182W) is responsible for the loss of interaction. We verify the implications garnered from the PqsE(E182W) structure using mutagenic, biochemical, and additional structural analyses. We present the next generation of molecules targeting the PqsE active site, including a structure of the tightest binding of these compounds, BB584, in complex with PqsE. The findings presented here provide insight for drug discovery against P. aeruginosa with PqsE as the target. Author SummaryThe human pathogen Pseudomonas aeruginosa is resistant to many currently used antibiotics, making it a burden of urgent clinical importance. P. aeruginosa pathogenicity is controlled by the bacterial cell-to-cell communication process called quorum sensing (QS). The function of one protein that controls P. aeruginosa QS-directed virulence, RhlR, requires a protein-protein interaction with an enzyme called PqsE. When PqsE is blocked from interacting with RhlR, P. aeruginosa is avirulent and incapable of infecting an animal host. Here, we validate the PqsE-RhlR interaction as a target for antibiotic development, and we present a mechanism for how such antibiotics could disrupt the PqsE-RhlR interaction. Discovery of new antibiotics would fulfill an unmet healthcare need by providing treatments to combat P. aeruginosa infections.

microbiology↗

Species-wide phylogenomics of the Staphylococcus aureus agr operon reveals convergent evolution of frameshift mutations

Staphylococcus aureus is a prominent nosocomial pathogen that causes several life-threatening diseases such as pneumonia and bacteremia. S. aureus modulates expression of its arsenal of virulence factors through sensing and integrating responses to environmental signals. The agr (accessory gene regulator) quorum sensing (QS) system is a major regulator of virulence phenotypes in S. aureus. There are four agr specificity groups each with a different autoinducer peptide sequence (encoded by the agrD gene). Though agr is critical for expression of many toxins, paradoxically, S. aureus strains often have non-functional agr activity due to loss-of-function mutations in the four-gene agr operon. To understand patterns in agr variability across S. aureus, we undertook a species-wide genomic investigation. We developed a software tool (AgrVATE; https://github.com/VishnuRaghuram94/AgrVATE) for typing and detecting frameshift mutations in the agr operon. In an analysis of over 40,000 S. aureus genomes, we showed close association between agr type and S. aureus clonal complex. We also found strong linkage between agrBDC alleles (encoding the peptidase, the autoinducing peptide itself, and the peptide sensor respectively) but not agrA (encoding the -response regulator). More than five percent of genomes were found to have frameshift mutations in the agr operon. Though most mutations occur only once in the entire species, we observed a small number of recurring mutations evolving convergently across different clonal lineages. Phylogenetic patterns suggested that strains with agr frameshifts were evolutionary dead ends. Overall, genomic analysis of agr operon suggests evolution through multiple processes with functional consequences that are not fully understood. ImportanceStaphylococcus aureus is a globally pervasive pathogen that produces a plethora of toxic molecules that can degrade, evade, or inhibit the host immune cells. Production of these toxins is mainly controlled by an active agr quorum sensing system, which senses and responds to bacterial cell density. However, there are many reports of S. aureus strains with genetic changes leading to impaired agr activity, often found during chronic bloodstream infections, and may be associated with increased disease severity. We developed an open-source software called AgrVATE to type agr systems and identify putative frameshifts. We used AgrVATE for a species-wide genomic survey of S. aureus, finding that more than 5 % of strains in the public database had non-functional agr systems. We also provide new insights into the evolution of these genetic mutations in the agr system. Overall, this study contributes to our understanding of a common but relatively understudied means of virulence regulation in S. aureus.

genomics↗

Cell surface hydrophobicity determines Pseudomonas aeruginosa aggregate assembly

Bacteria live in spatially organized aggregates during chronic infections, where they adapt to the host environment, evade immune responses and resist therapeutic interventions. Although it is known that environmental factors such as polymers influence bacterial aggregation, it is not clear how bacterial adaptation during chronic infection impacts the formation and spatial organization of aggregates in the presence of polymers. Here we show that in an in vitro model of cystic fibrosis (CF) containing the polymers eDNA and mucin, O-specific antigen is a major factor in determining the formation of two distinct aggregate assembly types of Pseudomonas aeruginosa due to alterations in cell surface hydrophobicity. Our findings suggest that during chronic infection, interplay between cell surface properties and polymers in the environment may influence the formation and structure of bacterial aggregates, which would shed new light on the fitness costs and benefits of O-antigen production in environments such as CF lungs. ImportanceDuring chronic infection, several factors contribute to the biogeography of microbial communities. Heterogeneous populations of Pseudomonas aeruginosa form aggregates in cystic fibrosis airways, however, the impact of this population heterogeneity on spatial organization and aggregate assembly is not well understood. In this study we found that changes in O-specific antigen determine the spatial organization of P. aeruginosa cells by altering the relative cell surface hydrophobicity. This finding suggests a role for O-antigen in regulating P. aeruginosa aggregate size and shape in cystic fibrosis airways.

microbiology↗

Overproduction of the AlgT sigma factor is lethal to mucoid Pseudomonas aeruginosa

Pseudomonas aeruginosa isolates from chronic lung infections often overproduce alginate, giving rise to the mucoid phenotype. Isolation of mucoid strains from chronic lung infections correlates with a poor patient outcome. The most common mutation that causes the mucoid phenotype is called mucA22 and results in a truncated form of the anti-sigma factor MucA that is continuously subjected to proteolysis. When a functional MucA is absent, the cognate sigma factor, AlgT, is no longer sequestered and continuously transcribes the alginate biosynthesis operon leading to alginate overproduction. In this work, we report that in the absence of wild-type MucA, providing exogenous AlgT is toxic. This is intriguing since mucoid strains endogenously possess high levels of AlgT. Furthermore, we show that suppressors of toxic AlgT production have mutations in mucP, a protease involved in MucA degradation, and provide the first atomistic model of MucP. Our findings support a model where mutations in mucP stabilize the truncated form of MucA22 rendering it functional and therefore able to reduce toxicity by properly sequestering AlgT. IMPORTANCEPseudomonas aeruginosa is an opportunistic bacterial pathogen capable of causing chronic lung infections. Phenotypes important for the long-term persistence and adaption to this unique lung ecosystem are largely regulated by the AlgT sigma factor. Chronic infection isolates often contain mutations in the anti-sigma factor mucA resulting in uncontrolled AlgT and continuous production of alginate, in addition to the expression of ~300 additional genes including algT itself. Here we report that in the absence of wild-type MucA, AlgT overproduction is lethal and that suppressors of toxic AlgT production have mutations in the MucA protease, MucP. Since AlgT contributes to the establishment of chronic infections, understanding how AlgT is regulated will provide vital information on how P. aeruginosa is capable of causing long-term infections.

microbiology↗

Genotypic and phenotypic diversity of Staphylococcus aureus from cystic fibrosis lung infections and their interactions with Pseudomonas aeruginosa

Pseudomonas aeruginosa and Staphylococcus aureus are the most common bacteria that infect the respiratory tract of individuals with the genetic disease cystic fibrosis (CF); in fact, S. aureus has recently overtaken P. aeruginosa to become the most common. Substantial research has been performed on the epidemiology of S. aureus in CF; however, there appears to be a gap in knowledge in regard to the pathogenesis of S. aureus in the context of CF lung infections. Most studies have focused on a few S. aureus isolates, often exclusively laboratory adapted strains, and how they are killed by P. aeruginosa. Because of this, little is known about the diversity of S. aureus CF lung isolates in both virulence and interaction with P. aeruginosa. To begin to address this gap in knowledge, we recently sequenced 65 clinical S. aureus isolates from the Emory CF Biospecimen Registry and Boston Childrens Hospital, including the reference isolate JE2, a USA300 strain. Here, we analyzed antibiotic resistance genotypes, sequence type, clonal complex, spa type, and agr type of these isolates. We hypothesized that major virulence phenotypes of S. aureus that may be associated with CF lung infections, namely toxin production and mucoid phenotype, would be retained in these isolates. To test our hypothesis, we plated on specific agars and found that most isolates can hemolyze both rabbit and sheep blood (67.7%) and produce polysaccharide (69.2%), consistent with virulence retention in CF lung isolates. We also identified three distinct phenotypic groups of S. aureus based on their survival in the presence of nonmucoid P. aeruginosa laboratory strain PAO1 and its mucoid derivative. Altogether, our work provides greater insight into the diversity of S. aureus CF isolates, specifically the distribution of important virulence factors and their interaction with P. aeruginosa, all of which have implications in patient health.\n\nAuthor SummaryStaphylococcus aureus is now the most frequently detected pathogen in the lungs of individuals who have cystic fibrosis (CF), followed closely by Pseudomonas aeruginosa. When these two pathogens are found to coinfect the CF lung, patients have a significantly worse prognosis. While P. aeruginosa has been rigorously studied in the context of bacterial pathogenesis in CF, less is known about S. aureus. Here we present an in-depth study of 64 S. aureus CF clinical isolates where we investigated genetic diversity utilizing whole genome sequencing, virulence phenotypes, and interactions with P. aeruginosa. We have found that S. aureus isolated from the CF lung are phylogenetically diverse, most retain known virulence factors, and they vary in interactions with P. aeruginosa from highly sensitive to completely tolerant. Deepening our understanding of how S. aureus responds to its environment and other microbes in the CF lung will enable future development of effective treatments and preventative measures against these formidable infections.

microbiology↗

Substrate recognition by the Pseudomonas aeruginosa EF-Tu methyltransferase EftM

Pseudomonas aeruginosa is an opportunistic pathogen and a leading cause of serious infections in individuals with cystic fibrosis, compromised immune systems, and severe burns. During infection, P. aeruginosa adhesion to host epithelial cells is enhanced by surface exposed translation elongation factor EF-Tu carrying a Lys5 trimethylation. This modification is incorporated by the S-adenosyl-L-methionine-dependent methyltransferase EftM. Thus, EF-Tu modification by EftM may represent a novel target to restrict the establishment of P. aeruginosa infections in vulnerable individuals. Here, we extend our understanding of EftM action by defining the molecular mechanism of EF-Tu substrate recognition by this enzyme. First, following the observation that EftM can bind to EF-Tu lacking an N-terminal peptide (encompassing the Lys5 target site), an EftM homology model was generated and used in protein-protein docking studies to predict EftM:EF-Tu interactions. The predicted protein-protein interface was then experimentally validated using site-directed mutagenesis of residues in both proteins coupled with binding and methyltransferase activity assays. We also show that EftM is unable to methylate the isolated N-terminal EF-Tu peptide and that binding-induced conformational changes in EftM are likely needed to allow placement of the first 5-6 amino acids of EF-Tu into the conserved peptide binding channel. In this channel, a group of residues that are highly conserved in EftM family proteins position the N-terminal sequence to facilitate modification of Lys5. Our findings provide detailed insights into substrate recognition by this lysine methyltransferase, paving the way for a deeper understanding of EftMs mechanism of action on EF-Tu.

biochemistry↗

Microbiome data enhances predictive models of lung function in people with CF

BackgroundMicrobiome sequencing has brought increasing attention to the polymicrobial context of chronic infections. However, clinical microbiology continues to focus on canonical human pathogens, which may overlook informative, but non-pathogenic, biomarkers. We address this disconnect in lung infections in people with cystic fibrosis (CF). MethodsWe collected health information (lung function, age, BMI) and sputum samples from a cohort of 77 children and adults with CF. Samples were collected during a period of clinical stability and 16S rDNA sequenced for airway microbiome compositions. We use Elastic Net regularization to train linear models predicting lung function and extract the most informative features. ResultsModels trained on whole microbiome quantitation outperform models trained on pathogen quantitation alone, with or without the inclusion of patient metadata. Our most accurate models retain key pathogens as negative predictors (Pseudomonas, Achromobacter) along with established correlates of CF disease state (age, BMI, CF related diabetes). In addition, our models select non-pathogen taxa (Fusobacterium, Rothia) as positive predictors of lung health. ConclusionsThese results support a reconsideration of clinical microbiology pipelines to ensure the provision of informative data to guide clinical practice.

bioinformatics↗