Gene Networks and Pathways Involved in Escherichia coli Response to Multiple Stressors

Bacterial extracellular vesicles target different bacterial species, impairing cell division and diminishing their pathogenicity

Extracellular vesicles (EVs) produced by bacteria contain many bacterial-derived molecules, which play an important role in host interactions and as mediators of bacterial communication. However, the role of EVs in interspecies interactions and their physiological and ecological significance are not well understood. In this study, we found that Escherichia coli EVs inhibit the growth of group A Streptococcus (GAS; Streptococcus pyogenes) by inducing defective cell division via the following processes. E. coli EVs first attach to the cell surface of GAS. In EV-attached GAS cells, multiple septa and Z-rings form in close proximity, which clearly differs from the typical cell division process. This is due to inhibition of peptidoglycan (PG) remodeling in the process after septum formation, in which the next cell division is initiated without completion of peripheral PG synthesis. Therefore, cell division proceeds while inducing cell elongation and cell separation failure, leading to growth inhibition. Furthermore, EV alters the expression of approximately 10% of all genes encoded on the GAS genome, and the diverse functions of these gene sets, which include replication, division, and metabolism, suggest that EVs have a variety of biological effects on the targeted bacterial cells. Notably, E. coli EVs significantly decreased the expression of genes involved in representative GAS virulence, such as slo, nga, and hasA, and also markedly attenuated the pathogenicity of GAS in mice. Our findings provide insight into the competitive functions of EVs between different bacterial species, expanding current knowledge on EV-mediated interspecies interactions.

Analysis of stress response in multiple bacterial pathogens using a network biology approach

Stress response in bacterial pathogens promotes adaptation, virulence and antibiotic resistance. In this study, a network approach is applied to identify the common central mediators of stress response in five emerging opportunistic pathogens; Enterococcus faecium Aus0004, Staphylococcus aureus subsp. aureus USA300, Klebsiella pneumoniae MGH 78,578, Pseudomonas aeruginosa PAO1, and Mycobacterium tuberculosis H37Rv. A Protein-protein interaction network (PPIN) was constructed for each stressor using Cytoscape3.7.1 from the differentially expressed genes obtained from Gene expression omnibus datasets. A merged PPIN was constructed for each bacterium. Hub-bottlenecks in each network were the central stress response proteins and common pathways enriched in stress response were identified using KOBAS3.0. 31 hub-bottlenecks were common to each individual stress response, merged networks in all five pathogens and an independent cross stress (CS) response dataset of Escherichia coli. The 31 central nodes are in the RpoS mediated general stress regulon and also regulated by other stress response systems. Analysis of the 20 common metabolic pathways modulating stress response in all five bacteria showed that carbon metabolism pathway had the highest crosstalk with other pathways like amino acid biosynthesis and purine metabolism pathways. The central proteins identified can serve as targets for novel wide-spectrum antibiotics to overcome multidrug resistance.

Antibiotic-induced stress responses in Gram-negative bacteria and their role in antibiotic resistance

Bacteria adapt to changes in their natural environment through a network of stress responses that enable them to alter their gene expression to survive in the presence of stressors, including antibiotics. These stress responses can be specific to the type of stress and the general stress response can be induced in parallel as a backup mechanism. In Gram-negative bacteria, various envelope stress responses are induced upon exposure to antibiotics that cause damage to the cell envelope or result in accumulation of toxic metabolic by-products, while the heat shock response is induced by antibiotics that cause misfolding or accumulation of protein aggregates. Antibiotics that result in the production of reactive oxygen species (ROS) induce the oxidative stress response and those that cause DNA damage, directly and through ROS production, induce the SOS response. These responses regulate the expression of various proteins that work to repair the damage that has been caused by antibiotic exposure. They can contribute to antibiotic resistance by refolding, degrading or removing misfolded proteins and other toxic metabolic by-products, including removal of the antibiotics themselves, or by mutagenic DNA repair. This review summarizes the stress responses induced by exposure to various antibiotics, highlighting their interconnected nature, as well the roles they play in antibiotic resistance, most commonly through the upregulation of efflux pumps. This can be useful for future investigations targeting these responses to combat antibiotic-resistant Gram-negative bacterial infections.

Multidimensional tolerance landscapes reveal antibiotic-environment interactions affecting population dynamics of wastewater bacteria

City sewers harbor diverse bacterial communities that are continuously exposed to a myriad of antibiotic residues resulting from human consumption and excretion. Despite their sub-inhibitory concentrations in sewage, these pharmaceutical residues affect the growth rate and the yield of susceptible wastewater-associated bacteria. Moreover, environmental conditions in sewers are complex, including variations in temperature and, in many coastal city sewers, salinity. These variables can modulate antibiotic tolerance and therefore affect the dynamics of microbial populations. To explore such interactions between antibiotics and abiotic environmental factors, we built continuous multivariate tolerance landscapes for three bacterial species commonly detected in sewage: Escherichia coli, the emerging pathogen Streptococcus suis, and a typical sewer dweller, Arcobacter cryaerophilus. We projected their intrinsic growth rate and carrying capacity onto a complex environment including temperature, salinity, and a range of concentrations of two antibiotics frequently measured in urban wastewater (ciprofloxacin and azithromycin). We revealed that antibiotic tolerance was maximal at salinities close to seawater for both E. coli and S. suis, and that the direction of the interaction between antibiotics and temperature is species dependent. In E. coli, we additionally observed a third-order interaction among salinity, temperature and antibiotics, highlighting the limits of predicting field dynamics of bacterial populations using standard laboratory measures. We projected these tolerance curves onto time series data of temperature and conductivity measured in the sewers of Barcelona. Our model highlights that low concentrations of antibiotics could exclude the most sensitive species, while interactions between antibiotics, temperature, and salinity substantially affected the dynamics of the more tolerant ones.

The hidden elephant: Modified abasic sites and their consequences

Abasic, or apurinic/apyrimidinic sites (AP sites) are among the most abundant DNA lesions, appearing in DNA both through spontaneous base loss and as intermediates of base excision DNA repair. Natural aldehydic AP sites have been known for decades and their interaction with the cellular replication, transcription and repair machinery has been investigated in detail. Oxidized AP sites, produced by free radical attack on intact nucleotides, received much attention recently due to their ability to trap DNA repair enzymes and chromatin structural proteins such as histones. In the past few years, it became clear that the reactive nature of aldehydic and oxidized AP sites produces a variety of modifications, including AP site-protein and AP site-peptide cross-links, adducts with small molecules of metabolic or xenobiotic origin, and AP site-mediated interstrand DNA cross-links. The diverse chemical nature of these common-origin lesions is reflected in the wide range of their biological consequences. In this review, we summarize the data on the mechanisms of modified AP sites generation, their abundance, the ability to block DNA polymerases or cause nucleotide misincorporation, and the pathways of their repair.

Proteomic insights into survival strategies of Escherichia coli in perchlorate-rich Martian brines

Brines, potentially formed by the deliquescence and freezing point depression of highly hygroscopic salts, such as perchlorates (ClO4-), may allow for the spatial and temporal stability of liquid water on present-day Mars. It is therefore of great interest to explore the microbial habitability of Martian brines, for which our current understanding is, however, still limited. Putative microbes growing in the perchlorate-rich Martian regolith may be harmed due to the induction of various stressors including osmotic, chaotropic, and oxidative stress. We adapted the model organism Escherichia coli to increasing sodium perchlorate concentrations and used a proteomic approach to characterize the adaptive phenotype. Separately, the microbe was adapted to elevated concentrations of sodium chloride and glycerol, which enabled us to distinguish perchlorate-specific adaptation mechanisms from those in response to osmotic, ion and water activity stress. We found that the perchlorate-specific stress response focused on pathways alleviating damage to nucleic acids, presumably caused by increased chaotropic and/or oxidative stress. The significant enrichments that have been found include DNA repair, RNA methylation and de novo inosine monophosphate (IMP) biosynthesis. Our study provides insights into the adaptive mechanisms necessary for microorganisms to survive under perchlorate stress, with implications for understanding the habitability of Martian brines.

The Dentin Microbiome: A Metatranscriptomic Evaluation of Caries-Associated Bacteria

Background/Objectives: Dental caries remains a prevalent chronic disease globally, driven by complex interactions between the host, diet, and microbial communities. This study employs a metatranscriptomic RNA-Seq analysis to explore the functional dynamics of the dentin microbiome in both healthy and carious teeth. By examining the transcriptional activity of bacterial communities, we aimed to identify key microbial species and molecular functions associated with caries progression. Methods: Samples from six patients (three healthy and three decayed teeth) were analyzed using the Illumina NovaSeq 2000 platform, with data processed through the SAMSA2 pipeline for taxonomic and functional annotation. Results: The differential expression analysis revealed significant upregulation of Streptococcus and Lactobacillus species, including S. mutans, S. sobrinus, and L. salivarius, in carious samples, highlighting their roles in acid production and carbohydrate metabolism. Additionally, Mycobacterium species, known for their biofilm-forming capabilities and acid tolerance, were upregulated in decayed teeth. The Gene Ontology (GO) enrichment analysis identified unique molecular functions and biological processes in carious teeth, such as carbohydrate metabolism, oxidative stress response, and bacterial cell wall biogenesis, which are critical for microbial survival in acidic environments. In contrast, healthy teeth exhibited functions related to homeostasis and nutrient acquisition, reflecting a balanced microbial community. Conclusions: The study underscores the polymicrobial nature of dental caries, with multiple bacterial species contributing to disease progression through diverse metabolic and stress-response mechanisms. These findings provide deeper insights into the ecological shifts within the oral microbiome during caries development, emphasizing the importance of a functional metatranscriptomic analysis in understanding the pathogenesis of dental caries.

High-throughput method characterizes hundreds of previously unknown antibiotic resistance mutations

A fundamental obstacle to tackling the antimicrobial resistance crisis is identifying mutations that lead to resistance in a given genomic background and environment. We present a high-throughput technique - Quantitative Mutational Scan sequencing (QMS-seq) - that enables quantitative comparison of which genes are under antibiotic selection and captures how genetic background influences resistance evolution. We compare four E. coli strains exposed to ciprofloxacin, cycloserine, or nitrofurantoin and identify 812 resistance mutations, many in genes and regulatory regions not previously associated with resistance. We find that multi-drug and antibiotic-specific resistance are acquired through categorically different types of mutations, and that minor genotypic differences significantly influence evolutionary routes to resistance. By quantifying mutation frequency with single base pair resolution, QMS-seq informs about the underlying mechanisms of resistance and identifies mutational hotspots within genes. Our method provides a way to rapidly screen for resistance mutations while assessing the impact of multiple confounding factors.

Understanding the Impact of Salt Stress on Plant Pathogens Through Phenotypic and Transcriptomic Analysis

For plant diseases to become established, plant pathogens require not only virulence factors and susceptible hosts, but also optimal environmental conditions. The accumulation of high soil salinity can have serious impacts on agro-biological ecosystems. However, the interactions between plant pathogens and salinity have not been fully characterized. This study investigated the effects of salt stress on representative plant pathogens, such as Burkholderia gladioli, Burkholderia glumae, Pectobacterium carotovorum subsp. carotovorum (Pcc), Ralstonia solanacearum, and Xanthomonas oryzae pv. oryzae. Phenotypic assays revealed that B. gladioli and R. solanacearum are highly sensitive to salt stress, exhibiting significant reductions in growth, motility, and enzyme production, whereas Pcc showed notable tolerance. Pan-genome-based comparative transcriptomics identified co-downregulated patterns in B. gladioli and R. solanacearum under stress conditions, indicating the suppression of bacterial chemotaxis and type III secretion systems. Uniquely upregulated patterns in Pcc were associated with enhanced survival under high salinity, such as protein quality control, osmotic equilibrium, and iron acquisition. Additionally, the application of salt stress combined with the beneficial bacterium Chryseobacterium salivictor significantly reduced tomato wilt caused by R. solanacearum, suggesting a potential management strategy. This study underscores practical implications for effectively understanding and controlling plant pathogens under future climate changes involving salt stress.

Dynamic heterogeneity in an E. coli stress response regulon mediates gene activation and antimicrobial peptide tolerance

The bacterial stress response is an intricately regulated system that plays a critical role in cellular resistance to drug treatment. The complexity of this response is further complicated by cell-to-cell heterogeneity in the expression of bacterial stress response genes. These genes are often organized into networks comprising one or more transcriptional regulators that control expression of a suite of downstream genes. While the expression heterogeneity of many of these upstream regulators has been characterized, the way in which this variability affects the larger downstream stress response remains hard to predict, prompting two key questions. First, how does heterogeneity and expression noise in stress response regulators propagate to the diverse downstream genes in their regulons. Second, when expression levels vary, how do multiple downstream genes act together to protect cells from stress. To address these questions, we focus on the transcription factor PhoP, a critical virulence regulator which coordinates pathogenicity in several gram-negative species. We use optogenetic stimulation to precisely control PhoP expression levels and examine how variations in PhoP affect the downstream activation of genes in the PhoP regulon. We find that these downstream genes exhibit differences both in mean expression level and sensitivity to increasing levels of PhoP. These response functions can also vary between individual cells, increasing heterogeneity in the population. We tie these variations to cell survival when bacteria are exposed to a clinically-relevant antimicrobial peptide, showing that high expression of the PhoP-regulon gene pmrD provides a protective effect against Polymyxin B. Overall, we demonstrate that even subtle heterogeneity in expression of a stress response regulator can have clear consequences for enabling bacteria to survive stress.

Base editor-mediated large-scale screening of functional mutations in bacteria for industrial phenotypes

Base editing, the targeted introduction of point mutations into cellular DNA, holds promise for improving genome-scale functional genome screening to single-nucleotide resolution. Current efforts in prokaryotes, however, remain confined to loss-of-function screens using the premature stop codons-mediated gene inactivation library, which falls far short of fully releasing the potential of base editors. Here, we developed a base editor-mediated functional single nucleotide variant screening pipeline in Escherichia coli. We constructed a library with 31,123 sgRNAs targeting 462 stress response-related genes in E. coli, and screened for adaptive mutations under isobutanol and furfural selective conditions. Guided by the screening results, we successfully identified several known and novel functional mutations. Our pipeline might be expanded to the optimization of other phenotypes or the strain engineering in other microorganisms.

Modulation of bacterial membranes and cellular macromolecules by dimethyl sulfoxide: A dose-dependent study providing novel insights

Using Escherichia coli as a model, this manuscript delves into the intricate interactions between dimethyl sulfoxide (DMSO) and membranes, cellular macromolecules, and the effects on various aspects of bacterial physiology. Given DMSO's wide-ranging use as a solvent in microbiology, we investigate the impacts of both non-growth inhibitory (1.0 % and 2.5 % v/v) and slightly growth-inhibitory (5.0 % v/v) concentrations of DMSO. The results demonstrate that DMSO causes alterations in bacterial membrane potential, influences the electrochemical characteristics of the cell surface, and exerts substantial effects on the composition and structure of cellular biomolecules. Genome-wide gene expression data from DMSO-treated E. coli was used to further investigate and bolster the results. The findings of this study provide valuable insights into the complex relationship between DMSO and biological systems, with potential implications in drug delivery and cellular manipulation. However, it is essential to exercise caution when utilizing DMSO to enhance the solubility and delivery of bioactive compounds, as even at low concentrations, DMSO exerts non-inert effects on cellular macromolecules and processes.

Regulatory Functions of PurR in Yersinia pestis: Orchestrating Diverse Biological Activities

The bacterium Yersinia pestis has developed various strategies to sense and respond to the complex stresses encountered during its transmission and pathogenic processes. PurR is a common transcriptional regulator of purine biosynthesis among microorganisms, and it modulates the transcription level of the pur operon to suppress the production of hypoxanthine nucleotide (IMP). This study aims to understand the functions and regulatory mechanisms of purR in Y. pestis. Firstly, we constructed a purR knockout mutant of Y. pestis strain 201 and compared certain phenotypes of the null mutant (201-ΔpurR) and the wild-type strain (201-WT). The results show that deleting purR has no significant impact on the biofilm formation, growth rate, or viability of Y. pestis under different stress conditions (heat and cold shock, high salinity, and hyperosmotic pressure). Although the cytotoxicity of the purR knockout mutant on HeLa and 293 cells is reduced, the animal-challenging test found no difference of the virulence in mice between 201-ΔpurR and 201-WT. Furthermore, RNA-seq and EMSA analyses demonstrate that PurR binds to the promoter regions of at least 15 genes in Y. pestis strain 201, primarily involved in purine biosynthesis, along with others not previously observed in other bacteria. Additionally, RNA-seq results suggest the presence of 11 potential operons, including a newly identified co-transcriptional T6SS cluster. Thus, aside from its role as a regulator of purine biosynthesis, purR in Y. pestis may have additional regulatory functions.

Characterization of phage vB_EcoS-EE09 infecting E. coli DSM613 Isolated from Wastewater Treatment Plant Effluent and Comparative Proteomics of the Infected and Non-Infected Host

Phages influence microbial communities, can be applied in phage therapy, or may serve as bioindicators, e.g., in (waste)water management. We here characterized the Escherichia phage vB_EcoS-EE09 isolated from an urban wastewater treatment plant effluent. Phage vB_EcoS-EE09 belongs to the genus Dhillonvirus, class Caudoviricetes. It has an icosahedral capsid with a long non-contractile tail and a dsDNA genome with an approximate size of 44 kb and a 54.6% GC content. Phage vB_EcoS-EE09 infected 12 out of the 17 E. coli strains tested. We identified 16 structural phage proteins, including the major capsid protein, in cell-free lysates by protein mass spectrometry. Comparative proteomics of protein extracts of infected E. coli cells revealed that proteins involved in amino acid and protein metabolism were more abundant in infected compared to non-infected cells. Among the proteins involved in the stress response, 74% were less abundant in the infected cultures compared to the non-infected controls, with six proteins showing significant less abundance. Repressing the expression of these proteins may be a phage strategy to evade host defense mechanisms. Our results contribute to diversifying phage collections, identifying structural proteins to enable better reliability in annotating taxonomically related phage genomes, and understanding phage-host interactions at the protein level.

A three-colour stress biosensor reveals multimodal response in single cells and spatiotemporal dynamics of biofilms

The plethora of stress factors that can damage microbial cells has evolved sophisticated stress response mechanisms. While existing bioreporters can monitor individual responses, sensors for detecting multimodal stress responses in living microorganisms are still lacking. Orthogonally detectable red, green, and blue fluorescent proteins combined in a single plasmid, dubbed RGB-S reporter, enable simultaneous, independent, and real-time analysis of the transcriptional response of Escherichia coli using three promoters which report physiological stress (PosmY for RpoS), genotoxicity (PsulA for SOS), and cytotoxicity (PgrpE for RpoH). The bioreporter is compatible with standard analysis and Fluorescent Activated Cell Sorting (FACS) combined with subsequent transcriptome analysis. Various stressors, including the biotechnologically relevant 2-propanol, activate one, two, or all three stress responses, which can significantly impact non-stress-related metabolic pathways. Implemented in microfluidic cultivation with confocal fluorescence microscopy imaging, the RGB-S reporter enabled spatiotemporal analysis of live biofilms revealing stratified subpopulations of bacteria with heterogeneous stress responses.

Characterization of Virulent T4-Like Acinetobacter baumannii Bacteriophages DLP1 and DLP2

The world is currently facing a global health crisis due to the rapid increase in antimicrobial-resistant bacterial infections. One of the most concerning pathogens is Acinetobacter baumannii, which is listed as a Priority 1 pathogen by the World Health Organization. This Gram-negative bacterium has many intrinsic antibiotic resistance mechanisms and the ability to quickly acquire new resistance determinants from its environment. A limited number of effective antibiotics against this pathogen complicates the treatment of A. baumannii infections. A potential treatment option that is rapidly gaining interest is “phage therapy”, or the clinical application of bacteriophages to selectively kill bacteria. The myoviruses DLP1 and DLP2 (vB_AbaM-DLP_1 and vB_AbaM-DLP_2, respectively) were isolated from sewage samples using a capsule minus variant of A. baumannii strain AB5075. Host range analysis of these phages against 107 A. baumannii strains shows a limited host range, infecting 15 and 21 for phages DLP1 and DLP2, respectively. Phage DLP1 has a large burst size of 239 PFU/cell, a latency period of 20 min, and virulence index of 0.93. In contrast, DLP2 has a smaller burst size of 24 PFU/cell, a latency period of 20 min, and virulence index of 0.86. Both phages show potential for use as therapeutics to combat A. baumannii infections.