Translation error clusters induced by aminoglycoside antibiotics

Comprehensive Analysis of Metabolites and Biological Endpoints Providing New Insights into the Tolerance of Wheat Under Sulfamethoxazole Stress

Metabolomics is a commonly used method to study the responses of organisms to environmental changes. However, the relationships between metabolites and biological endpoints still need further discussion. In this study, we exposed wheat seeds to sulfamethoxazole (0, 1, 10, 100 mg/L) for 5 days. The results show that sulfamethoxazole (SMX) had an inhibitory effect on wheat growth. It reduced shoot length, root length, shoot fresh weight, root fresh weight, chlorophyll content, and carotenoid content. At the same time, it increased the concentration of reactive oxygen species, the activity of superoxide dismutase, the activity of peroxidase, and the activity of catalase in the root. An orthogonal partial least squares analysis and correlation analysis were performed. SMX transformed five key metabolic pathways. Notably, certain metabolic alterations exhibited negative correlations with reactive oxygen species (ROS) accumulation and antioxidant enzyme activities (including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)), while showing positive associations with root growth parameters (fresh weight and length). Conversely, other metabolic changes appeared to promote ROS generation and enhance antioxidant enzyme activities, consequently inhibiting root growth. These findings offer novel perspectives on the metabolic regulation of wheat's stress response to SMX exposure.

Mechanism of read-through enhancement by aminoglycosides and mefloquine

Nonsense mutations are associated with numerous and diverse pathologies, yet effective treatment strategies remain elusive. A promising approach to combat these conditions involves the use of aminoglycosides, particularly in combination with stop-codon read-through enhancers, for developing drugs that can rescue the production of full-length proteins. Using X-ray crystallography and single-particle cryo-EM, we obtained structures of the eukaryotic ribosome in complexes with several aminoglycosides (geneticin G418, paromomycin, and hygromycin B) and the antimalarial drug mefloquine (MFQ), which has also been identified as a read-through enhancer. Our study reveals a binding site of MFQ, which holds significant promise for the development of therapies targeting premature termination codon-related genetic and oncological diseases. The results underscore the crucial role of the bridge B7b/c in mediating the effects of MFQ on subunit rotation dynamics. Through a comprehensive analysis of the interactions between the drugs and the eukaryotic ribosome, we propose a unifying hypothesis for read-through enhancement by small molecules, highlighting the role of decoding center rearrangements and intersubunit rotation dynamics.

Structural basis for hygromycin B inhibition of yeast pseudouridine-deficient ribosomes

Eukaryotic ribosomes are enriched with pseudouridine, particularly at the functional centers targeted by antibiotics. Here, we investigated the roles of pseudouridine in aminoglycoside-mediated translation inhibition by comparing the structural and functional properties of the yeast wild-type and the pseudouridine-free ribosomes. We showed that the pseudouridine-free ribosomes have decreased thermostability and high sensitivity to aminoglycosides. When presented with a model internal ribosomal entry site RNA, elongation factor eEF2, GTP (guanosine triphosphate), and sordarin, hygromycin B preferentially binds to the pseudouridine-free ribosomes during initiation by blocking eEF2 binding, stalling ribosomes in a nonrotated conformation. The structures captured hygromycin B bound at the intersubunit bridge B2a enriched with pseudouridine and a deformed codon-anticodon duplex, revealing a functional link between pseudouridine and aminoglycoside inhibition. Our results suggest that pseudouridine enhances both thermostability and conformational fitness of the ribosomes, thereby influencing their susceptibility to aminoglycosides.

Antibacterials exert toxic effects on aquatic organisms by inhibiting respiration, inducing oxidative stress, mitochondrial dysfunction and autophagy

Although bactericidal antibiotics are an integral part of infectious disease medicine, the uncontrolled use of these drugs in recent years is beginning to affect the environment, especially water resources. With the exception of a few well-documented toxic effects, antimicrobials are thought to act mainly on bacteria and, at low doses, have no deleterious effects on eukaryotic organisms. However, since mitochondria are direct ancient relatives of prokaryotes, mitochondrial dysfunction induced by antibiotic exposure can also occur in higher eukaryotes. In this work, we used the microcrustacean Artemia salina to show how some known antibacterial drugs exert toxic effects on mitochondria, suppressing cellular and organismal respiration in aquatic organisms. We have demonstrated that exposure to antimicrobials of different classes, namely kanamycin A, tetracycline hydrochloride, erythromycin, and chloramphenicol, leads to the accumulation of reactive oxygen species and is accompanied by autophagy. Our results suggest that the emergence of antibactericidal drugs, increasingly appearing in wastewater, may have far-reaching consequences for aquatic areas adjacent to large cities.

The role of bacterial metabolism in antimicrobial resistance

The relationship between bacterial metabolism and antibiotic treatment is complex. On the one hand, antibiotics leverage cell metabolism to function. On the other hand, increasing research has highlighted that the metabolic state of the cell also impacts all aspects of antibiotic biology, from drug efficacy to the evolution of antimicrobial resistance (AMR). Given that AMR is a growing threat to the current global antibiotic arsenal and ability to treat infectious diseases, understanding these relationships is key to improving both public and human health. However, quantifying the contribution of metabolism to antibiotic activity and subsequent bacterial evolution has often proven challenging. In this Review, we discuss the complex and often bidirectional relationships between metabolism and the various facets of antibiotic treatment and response. We first summarize how antibiotics leverage metabolism for their function. We then focus on the converse of this relationship by specifically delineating the unique contribution of metabolism to three distinct but related arms of antibiotic biology: antibiotic efficacy, AMR evolution and AMR mechanisms. Finally, we note the relevance of metabolism in clinical contexts and explore the future of metabolic-based strategies for personalized antimicrobial therapies. A deeper understanding of these connections is crucial for the broader scientific community to address the growing crisis of AMR and develop future effective therapeutics.

Mussel-Inspired In Situ Photodynamic Antibacterial Coating for Postoperative Management of Artificial Corneas

Artificial corneal (AC) implants offer hope to millions with corneal blindness, including 5 million in China. Titanium is one of the materials commonly used in the fabrication of artificial corneal scaffolders because of its light texture, high mechanical properties, and high biosafety. However, postoperative bacterial infections, especially from Pseudomonas aeruginosa and Staphylococcus aureus (S. aureus), remain a significant challenge due to the bioinert nature of titanium materials, leading to high infection rates. In this study, we introduce an innovative in situ photodynamic coating technology designed to manage postoperative infections in artificial corneas. Inspired by mussel adhesive proteins, this coating employs a composite of APTES-TA formed by Schiff base and Michael addition reactions between 3-aminopropyltriethoxysilane (APTES) and tannic acid (TA), integrated with the bacterial targeting capabilities of 4-carboxyphenylboronic acid (CPBA) and the photo-Fenton activity of FeOOH (iron(III) hydroxide). The design of the AC@APTES-TA-CPBA-FeOOH coating leverages the dynamic boronate ester bonds, which interact specifically with bacteria in tears, effectively capturing them on the surface of the artificial cornea. The coating exhibits a photocatalytic Fenton-like effect, which confers it with an exceptional bactericidal efficiency of over 99% in vitro. Furthermore, it demonstrates excellent protective functionality for mouse corneas in vivo experiments.

Efficacy of Larimichthys crocea TASOR protein-derived peptide FAM286 against Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a major foodborne pathogen, could lead cause of intestinal infections in humans. Antimicrobial peptides, as emerging antimicrobial agents, are gradually replacing traditional agents due to their highly effective and safe antimicrobial activity. In this study, a novel peptide, designated as FAM286, was identified from TASOR protein of Larimichthys crocea, which had a strong antimicrobial activity against S. aureus with a minimum bactericidal concentration (MBC) of 3.9 μg/mL and completed bacteria killing by treatment for 1.5 h. The FAM286 could increase the permeability and disrupt the integrity of cell membranes. The cell showed aggregation phenomenon and entered the apoptosis stage. In addition, the non-bactericidal concentration of FAM286 could effectively inhibit the formation of biofilm and remove mature biofilm. Molecular docking experiments further verified the binding sites of FAM286 to S. aureus biofilm proteins SarA, AgrA, and Hld. FAM286 could also bind the bacterial DNA in an embedded manner, disrupting the structure of DNA and leading to the death of bacteria. This study comprehensively evaluated the antimicrobial mechanism of the FAM286 against S. aureus and provided a theoretical basis for the prevention and control of S. aureus.

Antibiotics change the population growth rate heterogeneity and morphology of bacteria

A better understanding of the system-level effects of antibiotics on bacterial cells is essential to address the growing challenge of antibiotic resistance. Utilising Multipad Agarose Plate (MAP) platforms, we monitor the growth rate and cell morphology of three clinically relevant species (E.coli, S.aureus and P.aeruginosa) following exposure to 14 antibiotics across 11 concentrations (31 microbe-antibiotic combinations in total). Our results reveal a consistent increase in population growth rate heterogeneity (PGRH) as drug concentrations approach the minimum inhibitory concentration (MIC). Strikingly, the magnitude of this heterogeneity correlates with the functional distance between the ribosome and the specific cellular processes targeted by the antibiotics. Among the seven antibiotic classes studied, protein synthesis inhibitors and disruptors cause the lowest PGRH, while heterogeneity progressively increases with RNA synthesis inhibitors, DNA replication inhibitors, cell membrane disruptors and cell wall synthesis inhibitors. Because the ribosome is central to growth rate control, we hypothesize that heterogeneity might arise at the system level as a result of the propagation of damage to protein synthesis. Low heterogeneity is desirable from a clinical perspective, as high heterogeneity is often associated with persistence and treatment survival. Additionally, we observed a strong correlation between morphological alterations and growth inhibition across all antibiotics and species tested. This led to the development of a novel morphological parameter, MOR50, which enables rapid estimation of MIC for antibiotic susceptibility testing (AST) with a single snapshot after just 2.5 hours of incubation. In addition to introducing a novel, resource-efficient and rapid AST method, our findings shed new light on the system-level effects of antibiotic perturbations on bacteria, which might inform treatment design.

Development of a highly sensitive method to detect translational infidelity

Protein homeostasis (proteostasis) is the balance of protein synthesis, protein maintenance, and degradation. Loss of proteostasis contributes to the aging process and characterizes neurodegenerative diseases. It is well established that the processes of protein maintenance and degradation are declining with aging; however, the contribution of a declining quality of protein synthesis to the loss of proteostasis is less well understood. In fact, protein synthesis at the ribosome is an error-prone process and challenges the cell with misfolded proteins. Here, we present the development of a highly sensitive and reproducible reporter assay for the detection of translational errors and the measurement of translational fidelity. Using Nano-luciferase, an enzyme 3 times smaller and 50 times more sensitive than the hitherto used Firefly-luciferase, we introduced stop-codon and amino-acid exchanges that inactivate the enzyme. Erroneous re-activation of luciferase activity indicates ribosomal inaccuracy and translational infidelity. This highly sensitive and reproducible method has broad applications for studying the molecular mechanisms underlying diseases associated with defective protein synthesis and can be used for drug screening to modulate translational fidelity.

Unveil the Molecular Interplay between Aminoglycosides and Pseudouridine in IRES Translation

Eukaryotic ribosomes are enriched with pseudouridine, particularly at the functional centers targeted by antibiotics. Here we investigated the roles of pseudouridine in aminoglycoside-mediated translation inhibition by comparing the structural and functional properties of the wild-type ribosomes and those lacking pseudouridine ( cbf5 -D95A). We showed that the cbf5 -D95A ribosomes have decreased thermostability and high sensitivity to aminoglycosides. When presented with an internal ribosome entry site (IRES) RNA, elongation factor eEF2, GTP, sordarin, hygromycin B preferentially binds to the cbf5 -D95A ribosomes during initiation by blocking eEF2 binding and stalls the ribosomes in a non-rotated conformation, further hindering translocation. Hygromycin B binds to the inter-subunit bridge B2a that is known to be sensitive to pseudouridine, revealing a functional link between pseudouridine and aminoglycoside inhibition. Our results suggest that pseudouridine enhances both thermostability and conformational fitness of the ribosomes, thereby influencing their susceptibility to aminoglycosides.

Highlights

Loss of pseudouridine increases cell sensitivity to aminoglycosidesPseudouridine enhances ribosome thermostabilityHygromycin B competes with eEF2 for the non-rotated ribosomeHygromycin B deforms the codon-anticodon duplex.

The central role of transfer RNAs in mistranslation

Transfer RNAs (tRNA) are essential small non-coding RNAs that enable the translation of genomic information into proteins in all life forms. The principal function of tRNAs is to bring amino acid building blocks to the ribosomes for protein synthesis. In the ribosome, tRNAs interact with messenger RNA (mRNA) to mediate the incorporation of amino acids into a growing polypeptide chain following the rules of the genetic code. Accurate interpretation of the genetic code requires tRNAs to carry amino acids matching their anticodon identity and decode the correct codon on mRNAs. Errors in these steps cause the translation of codons with the wrong amino acids (mistranslation), compromising the accurate flow of information from DNA to proteins. Accumulation of mutant proteins due to mistranslation jeopardizes proteostasis and cellular viability. However, the concept of mistranslation is evolving, with increasing evidence indicating that mistranslation can be used as a mechanism for survival and acclimatization to environmental conditions. In this review, we discuss the central role of tRNAs in modulating translational fidelity through their dynamic and complex interplay with translation factors. We summarize recent discoveries of mistranslating tRNAs and describe the underlying molecular mechanisms and the specific conditions and environments that enable and promote mistranslation.

Process, advances, and perspectives of graphene oxide-SELEX for the development of aptamer molecular probes: A comprehensive review

BACKGROUND

Aptamers are screened via the systematic evolution of ligands by exponential enrichment (SELEX) and are widely used in molecular diagnostics and targeted therapies. The development of efficient and convenient SELEX technology has facilitated rapid access to high-performance aptamers, thereby advancing the aptamer industry. Graphene oxide (GO) serves as an immobilization matrix for libraries in GO-SELEX, making it suitable for screening aptamers against diverse targets.

RESULTS

This review summarizes the detailed steps involved in GO-SELEX, including monitoring methods, various sublibrary acquisition methods, and practical applications from its inception to the present day. In addition, the potential of GO-SELEX in the development of broad-spectrum aptamers is explored, and its current limitations for future development are emphasized. This review effectively promotes the application of the GO-SELEX technique by providing valuable insights and assisting researchers interested in conducting related studies.

SIGNIFICANCE AND NOVELTY

To date, no review on the topic of GO-SELEX has been published, making it challenging for researchers to initiate studies in this area. We believe that this review will broaden the SELEX options available to researchers, ensuring that they can meet the growing demand for molecular probes in the scientific domain.

Sophisticated natural products as antibiotics

In this Review, we explore natural product antibiotics that do more than simply inhibit an active site of an essential enzyme. We review these compounds to provide inspiration for the design of much-needed new antibacterial agents, and examine the complex mechanisms that have evolved to effectively target bacteria, including covalent binders, inhibitors of resistance, compounds that utilize self-promoted entry, those that evade resistance, prodrugs, target corrupters, inhibitors of 'undruggable' targets, compounds that form supramolecular complexes, and selective membrane-acting agents. These are exemplified by β-lactams that bind covalently to inhibit transpeptidases and β-lactamases, siderophore chimeras that hijack import mechanisms to smuggle antibiotics into the cell, compounds that are activated by bacterial enzymes to produce reactive molecules, and antibiotics such as aminoglycosides that corrupt, rather than merely inhibit, their targets. Some of these mechanisms are highly sophisticated, such as the preformed β-strands of darobactins that target the undruggable β-barrel chaperone BamA, or teixobactin, which binds to a precursor of peptidoglycan and then forms a supramolecular structure that damages the membrane, impeding the emergence of resistance. Many of the compounds exhibit more than one notable feature, such as resistance evasion and target corruption. Understanding the surprising complexity of the best antimicrobial compounds provides a roadmap for developing novel compounds to address the antimicrobial resistance crisis by mining for new natural products and inspiring us to design similarly sophisticated antibiotics.

Inactivation of the ribosome assembly factor RimP causes streptomycin resistance and impairs motility in Salmonella

The ribosome is the central hub for protein synthesis and the target of many antibiotics. Although the majority of ribosome-targeting antibiotics inhibit protein synthesis and are bacteriostatic, aminoglycosides promote protein mistranslation and are bactericidal. Understanding the resistance mechanisms of bacteria against aminoglycosides is not only vital for improving the efficacy of this critically important group of antibiotics but also crucial for studying the molecular basis of translational fidelity. In this work, we analyzed Salmonella mutants evolved in the presence of the aminoglycoside streptomycin (Str) and identified a novel gene rimP to be involved in Str resistance. RimP is a ribosome assembly factor critical for the maturation of the 30S small subunit that binds Str. Deficiency in RimP increases resistance against Str and facilitates the development of even higher resistance. Deleting rimP decreases mistranslation and cellular uptake of Str and further impairs flagellar motility. Our work thus highlights a previously unknown mechanism of aminoglycoside resistance via defective ribosome assembly.

Environment modulates protein heterogeneity through transcriptional and translational stop codon readthrough

Stop codon readthrough events give rise to longer proteins, which may alter the protein's function, thereby generating short-lasting phenotypic variability from a single gene. In order to systematically assess the frequency and origin of stop codon readthrough events, we designed a library of reporters. We introduced premature stop codons into mScarlet, which enabled high-throughput quantification of protein synthesis termination errors in E. coli using fluorescent microscopy. We found that under stress conditions, stop codon readthrough may occur at rates as high as 80%, depending on the nucleotide context, suggesting that evolution frequently samples stop codon readthrough events. The analysis of selected reporters by mass spectrometry and RNA-seq showed that not only translation but also transcription errors contribute to stop codon readthrough. The RNA polymerase was more likely to misincorporate a nucleotide at premature stop codons. Proteome-wide detection of stop codon readthrough by mass spectrometry revealed that temperature regulated the expression of cryptic sequences generated by stop codon readthrough in E. coli. Overall, our findings suggest that the environment affects the accuracy of protein production, which increases protein heterogeneity when the organisms need to adapt to new conditions.

Evolving precision: rRNA expansion segment 7S modulates translation velocity and accuracy in eukaryal ribosomes

Ribosome-enhanced translational miscoding of the genetic code causes protein dysfunction and loss of cellular fitness. During evolution, open reading frame length increased, necessitating mechanisms for enhanced translation fidelity. Indeed, eukaryal ribosomes are more accurate than bacterial counterparts, despite their virtually identical, conserved active centers. During the evolution of eukaryotic organisms ribosome expansions at the rRNA and protein level occurred, which potentially increases the options for translation regulation and cotranslational events. Here we tested the hypothesis that ribosomal RNA expansions can modulate the core function of the ribosome, faithful protein synthesis. We demonstrate that a short expansion segment present in all eukaryotes' small subunit, ES7S, is crucial for accurate protein synthesis as its presence adjusts codon-specific velocities and guarantees high levels of cognate tRNA selection. Deletion of ES7S in yeast enhances mistranslation and causes protein destabilization and aggregation, dramatically reducing cellular fitness. Removal of ES7S did not alter ribosome architecture but altered the structural dynamics of inter-subunit bridges thus affecting A-tRNA selection. Exchanging the yeast ES7S sequence with the human ES7S increases accuracy whereas shortening causes the opposite effect. Our study demonstrates that ES7S provided eukaryal ribosomes with higher accuracy without perturbing the structurally conserved decoding center.

Fit for Purpose Approach To Evaluate Detection of Amino Acid Substitutions in Shotgun Proteomics

Amino acid substitutions (AASs) alter proteins from their genome-expected sequences. Accumulation of substitutions in proteins underlies numerous diseases and antibiotic mechanisms. Accurate global detection of AASs and their frequencies is crucial for understanding these mechanisms. Shotgun proteomics provides an untargeted method for measuring AASs but introduces biases when extrapolating from the genome to identify AASs. To characterize these biases, we created a "ground-truth" approach using the similarities betweenEscherichia coli and Salmonella typhimurium to model the complexity of AAS detection. Shotgun proteomics on mixed lysates generated libraries representing ∼100,000 peptide-spectra and 4161 peptide sequences with a single AAS and defined stoichiometry. Identifying S. typhimurium peptide-spectra with only the E. coli genome resulted in 64.1% correctly identified library peptides. Specific AASs exhibit variable identification efficiencies. There was no inherent bias from the stoichiometry of the substitutions. Short peptides and AASs localized near peptide termini had poor identification efficiency. We identify a new class of "scissor substitutions" that gain or lose protease cleavage sites. Scissor substitutions also had poor identification efficiency. This ground-truth AAS library reveals various sources of bias, which will guide the application of shotgun proteomics to validate AAS hypotheses.

Dynamics and quantitative contribution of the aminoglycoside 6'-N-acetyltransferase type Ib to amikacin resistance

Aminoglycosides are essential components in the available armamentarium to treat bacterial infections. The surge and rapid dissemination of resistance genes strongly reduce their efficiency, compromising public health. Among the multitude of modifying enzymes that confer resistance to aminoglycosides, the aminoglycoside 6'-N-acetyltransferase type Ib [AAC(6')-Ib] is the most prevalent and relevant in the clinical setting as it can inactivate numerous aminoglycosides, such as amikacin. Although the mechanism of action, structure, and biochemical properties of the AAC(6')-Ib protein have been extensively studied, the contribution of the intracellular milieu to its activity remains unclear. In this work, we used a fluorescent-based system to quantify the number of AAC(6')-Ib per cell in Escherichia coli, and we modulated this copy number with the CRISPR interference method. These tools were then used to correlate enzyme concentrations with amikacin resistance levels. Our results show that resistance to amikacin increases linearly with a higher concentration of AAC(6')-Ib until it reaches a plateau at a specific protein concentration. In vivo imaging of this protein shows that it diffuses freely within the cytoplasm of the cell, but it tends to form inclusion bodies at higher concentrations in rich culture media. Addition of a chelating agent completely dissolves these aggregates and partially prevents the plateau in the resistance level, suggesting that AAC(6')-Ib aggregation lowers resistance to amikacin. These results provide the first step in understanding the cellular impact of each AAC(6')-Ib molecule on aminoglycoside resistance. They also highlight the importance of studying its dynamic behavior within the cell.IMPORTANCEAntibiotic resistance is a growing threat to human health. Understanding antibiotic resistance mechanisms can serve as foundation for developing innovative treatment strategies to counter this threat. While numerous studies clarified the genetics and dissemination of resistance genes and explored biochemical and structural features of resistance enzymes, their molecular dynamics and individual contribution to resistance within the cellular context remain unknown. Here, we examined this relationship modulating expression levels of aminoglycoside 6'-N-acetyltransferase type Ib, an enzyme of clinical relevance. We show a linear correlation between copy number of the enzyme per cell and amikacin resistance levels up to a threshold where resistance plateaus. We propose that at concentrations below the threshold, the enzyme diffuses freely in the cytoplasm but aggregates at the cell poles at concentrations over the threshold. This research opens promising avenues for studying enzyme solubility's impact on resistance, creating opportunities for future approaches to counter resistance.

Fluorescent reporters give new insights into antibiotics-induced nonsense and frameshift mistranslation

We developed a reporter system based on simultaneous expression of two fluorescent proteins: GFP as a reporter of the capacity of protein synthesis and mutated mScarlet-I as a reporter of translational errors. Because of the unique stop codons or frameshift mutations introduced into the mScarlet-I gene, red fluorescence was produced only after a mistranslation event. These reporters allowed us to estimate mistranslation at a single cell level using either flow cytometry or fluorescence microscopy. We found that laboratory strains of Escherichia coli are more prone to mistranslation compared to the clinical isolates. As relevant for uropathogenic E. coli, growth in human urine elevated translational frameshifting compared to standard laboratory media, whereas different standard media had a small effect on translational fidelity. Antibiotic-induced mistranslation was studied by using amikacin (aminoglycoside family) and azithromycin (macrolide family). Bactericidal amikacin induced preferably stop-codon readthrough at a moderate level. Bacteriostatic azithromycin on the other hand induced both frameshifting and stop-codon readthrough at much higher level. Single cell analysis revealed that fluorescent reporter-protein signal can be lost due to leakage from a fraction of bacteria in the presence of antibiotics, demonstrating the complexity of the antimicrobial activity.

Fitness Effects of Phenotypic Mutations at Proteome-Scale Reveal Optimality of Translation Machinery

Errors in protein translation can lead to non-genetic, phenotypic mutations, including amino acid misincorporations. While phenotypic mutations can increase protein diversity, the systematic characterization of their proteome-wide frequencies and their evolutionary impact has been lacking. Here, we developed a mechanistic model of translation errors to investigate how selection acts on protein populations produced by amino acid misincorporations. We fitted the model to empirical observations of misincorporations obtained from over a hundred mass spectrometry datasets of E. coli and S. cerevisiae. We found that on average 20% to 23% of proteins synthesized in the cell are expected to harbor at least one amino acid misincorporation, and that deleterious misincorporations are less likely to occur. Combining misincorporation probabilities and the estimated fitness effects of amino acid substitutions in a population genetics framework, we found 74% of mistranslation events in E. coli and 94% in S. cerevisiae to be neutral. We further show that the set of available synonymous tRNAs is subject to evolutionary pressure, as the presence of missing tRNAs would increase codon-anticodon cross-reactivity and misincorporation error rates. Overall, we find that the translation machinery is likely optimal in E. coli and S. cerevisiae and that both local solutions at the level of codons and a global solution such as the tRNA pool can mitigate the impact of translation errors. We provide a framework to study the evolutionary impact of codon-specific translation errors and a method for their proteome-wide detection across organisms and conditions.

Unveiling Synergistic Potency: Exploring Butyrolactone I to Enhance Gentamicin Efficacy against Methicillin-Resistant Staphylococcus aureus (MRSA) Strain USA300

Staphylococcus aureus, including MRSA strains, poses significant health risks, imposing a significant disease burden and mortality. We investigate butyrolactone I (BL-1), a marine-derived metabolite from Aspergillus terreus, enhancing aminoglycoside efficacy against MRSA. A promising synergy is observed with BL-1 and various aminoglycosides, marked by low fractional inhibitory concentration indexes (FICIs < 0.5). Comprehensive studies utilizing USA300 MRSA and gentamicin reveal a remarkable one-fourth reduction in minimum inhibitory concentration (MIC) with 20 μg/mL BL-1. A relative abundance assay indicates that BL-1 enhances gentamicin uptake while restraining extracellular presence, involving intricate transmembrane signaling and molecular interactions. RNA-Seq analysis yielded an unexpected revelation, unveiling a distinctive gene expression profile and distinguishing it from other treatment approaches. Furthermore, meticulous analyses validated the extensive perturbations induced by BL-1 exposure, affecting diverse biological functions, encompassing glycolysis, amino acid metabolisms, substance transmembrane transport, and virulence generation. These valuable insights inspired further confirmation of bacterial virulence and the modulation of membrane permeability resulting from BL-1 treatment. Phenotypic validations corroborated our observations, revealing reduced membrane permeability and hemolytic toxicity, albeit demanding a deeper comprehension of the intricate interplay underlying these actions. Our study contributes crucial mechanistic insights to the development of therapeutic strategies against this notorious pathogen and the judicious employment of aminoglycosides. Additionally, it elucidates marine-derived metabolites' ecological and functional roles, exemplified by fungal quorum sensing signals. These compounds could give producers a competitive edge, inhibiting microorganism proliferation and suggesting novel approaches for combating resistant pathogens.

Development of 2nd generation aminomethyl spectinomycins that overcome native efflux in Mycobacterium abscessus

Mycobacterium abscessus (Mab), a nontuberculous mycobacterial (NTM) species, is an emerging pathogen with high intrinsic drug resistance. Current standard-of-care therapy results in poor outcomes, demonstrating the urgent need to develop effective antimycobacterial regimens. Through synthetic modification of spectinomycin (SPC), we have identified a distinct structural subclass of N-ethylene linked aminomethyl SPCs (eAmSPCs) that are up to 64-fold more potent against Mab over the parent SPC. Mechanism of action and crystallography studies demonstrate that the eAmSPCs display a mode of ribosomal inhibition consistent with SPC. However, they exert their increased antimicrobial activity through enhanced accumulation, largely by circumventing efflux mechanisms. The N-ethylene linkage within this series plays a critical role in avoiding TetV-mediated efflux, as lead eAmSPC 2593 displays a mere fourfold susceptibility improvement against Mab ΔtetV, in contrast to the 64-fold increase for SPC. Even a minor shortening of the linkage by a single carbon, akin to 1st generation AmSPC 1950, results in a substantial increase in MICs and a 16-fold rise in susceptibility against Mab ΔtetV. These shifts suggest that longer linkages might modify the kinetics of drug expulsion by TetV, ultimately shifting the equilibrium towards heightened intracellular concentrations and enhanced antimicrobial efficacy. Furthermore, lead eAmSPCs were also shown to synergize with various classes of anti-Mab antibiotics and retain activity against clinical isolates and other mycobacterial strains. Encouraging pharmacokinetic profiles coupled with robust efficacy in Mab murine infection models suggest that eAmSPCs hold the potential to be developed into treatments for Mab and other NTM infections.

Deficiency in ribosome biogenesis causes streptomycin resistance and impairs motility in Salmonella

The ribosome is the central hub for protein synthesis and the target of many antibiotics. Whereas the majority of ribosome-targeting antibiotics inhibit protein synthesis and are bacteriostatic, aminoglycosides promote protein mistranslation and are bactericidal. Understanding the resistance mechanisms of bacteria against aminoglycosides is not only vital for improving the efficacy of this critically important group of antibiotics but also crucial for studying the molecular basis of translational fidelity. In this work, we analyzed Salmonella mutants evolved in the presence of the aminoglycoside streptomycin (Str) and identified a novel gene rimP to be involved in Str resistance. RimP is a ribosome assembly factor critical for the maturation of the 30S small subunit that binds Str. Deficiency in RimP increases resistance against Str and facilitates the development of even higher resistance. Deleting rimP decreases mistranslation and cellular uptake of Str, and further impairs flagellar motility. Our work thus highlights a previously unknown mechanism of aminoglycoside resistance via defective ribosome assembly.

En Route to Targeted Ribosome Editing to Replenish Skin Anchor Protein LAMB3 in Junctional Epidermolysis Bullosa

Severe junctional epidermolysis bullosa is a rare genetic, postpartum lethal skin disease, predominantly caused by nonsense/premature termination codon (PTC) sequence variants in LAMB3 gene. LAMB3 encodes LAMB3, the β subunit of epidermal-dermal skin anchor laminin 332. Most translational reads of a PTC mRNA deliver truncated, nonfunctional proteins, whereas an endogenous PTC readthrough mechanism produces full-length protein at minimal and insufficient levels. Conventional translational readthrough-inducing drugs amplify endogenous PTC readthrough; however, translational readthrough-inducing drugs are either proteotoxic or nonselective. Ribosome editing is a more selective and less toxic strategy. This technique identified ribosomal protein L35/uL29 (ie, RpL35) and RpL35-ligands repurposable drugs artesunate and atazanavir as molecular tools to increase production levels of full-length LAMB3. To evaluate ligand activity in living cells, we monitored artesunate and atazanavir treatment by dual luciferase reporter assays. Production levels of full-length LAMB3 increased up to 200% upon artesunate treatment, up to 150% upon atazanavir treatment, and up to 170% upon combinatorial treatment of RpL35 ligands at reduced drug dosage, with an unrelated PTC reporter being nonresponsive. Proof of bioactivity of RpL35 ligands in selective increase of full-length LAMB3 provides the basis for an alternative, targeted therapeutic route to replenish LAMB3 in severe junctional epidermolysis bullosa.

Aminoglycoside uptake, stress, and potentiation in Gram-negative bacteria: new therapies with old molecules

SUMMARYAminoglycosides (AGs) are long-known molecules successfully used against Gram-negative pathogens. While their use declined with the discovery of new antibiotics, they are now classified as critically important molecules because of their effectiveness against multidrug-resistant bacteria. While they can efficiently cross the Gram-negative envelope, the mechanism of AG entry is still incompletely understood, although this comprehension is essential for the development of new therapies in the face of the alarming increase in antibiotic resistance. Increasing antibiotic uptake in bacteria is one strategy to enhance effective treatments. This review aims, first, to consolidate old and recent knowledge about AG uptake; second, to explore the connection between AG-dependent bacterial stress and drug uptake; and finally, to present new strategies of potentiation of AG uptake for more efficient antibiotic therapies. In particular, we emphasize on the connection between sugar transport and AG potentiation.

Dynamics and quantitative contribution of the aminoglycoside 6'-N-acetyltransferase type Ib [AAC(6')-Ib] to amikacin resistance

Aminoglycosides are essential components in the available armamentarium to treat bacterial infections. The surge and rapid dissemination of resistance genes strongly reduce their efficiency, compromising public health. Among the multitude of modifying enzymes that confer resistance to aminoglycosides, the aminoglycoside acetyltransferase AAC(6')-Ib is the most prevalent and relevant in the clinical setting as it can inactivate numerous aminoglycosides, such as amikacin. Although the mechanism of action, structure, and biochemical properties of the AAC(6')-Ib protein have been extensively studied, the contribution of the intracellular milieu to its activity remains unclear. In this work, we used a fluorescent-based system to quantify the number of AAC(6')-Ib per cell in Escherichia coli, and we modulated this copy number with the CRISPR interference method. These tools were then used to correlate enzyme concentrations with amikacin resistance levels. Our results show that resistance to amikacin increases linearly with a higher concentration of AAC(6')-Ib until it reaches a plateau at a specific protein concentration. In vivo imaging of this protein shows that it diffuses freely within the cytoplasm of the cell, but it tends to form inclusion bodies at higher concentrations in rich culture media. Addition of a chelating agent completely dissolves these aggregates and partially prevents the plateau in the resistance level, suggesting that AAC(6')-Ib aggregation lowers resistance to amikacin. These results provide the first step in understanding the cellular impact of each AAC(6')-Ib molecule on aminoglycoside resistance. They also highlight the importance of studying its dynamic behavior within the cell.

Transfer RNA-mediated restoration of potassium current and electrical correction in premature termination long-QT syndrome hERG mutants

Disease-causing premature termination codons (PTCs) individually disrupt the functional expression of hundreds of genes and represent a pernicious clinical challenge. In the heart, loss-of-function mutations in the hERG potassium channel account for approximately 30% of long-QT syndrome arrhythmia, a lethal cardiac disorder with limited treatment options. Premature termination of ribosomal translation produces a truncated and, for potassium channels, a potentially dominant-negative protein that impairs the functional assembly of the wild-type homotetrameric hERG channel complex. We used high-throughput flow cytometry and patch-clamp electrophysiology to assess the trafficking and voltage-dependent activity of hERG channels carrying patient PTC variants that have been corrected by anticodon engineered tRNA. Adenoviral-mediated expression of mutant hERG channels in cultured adult guinea pig cardiomyocytes prolonged action potential durations, and this deleterious effect was corrected upon adenoviral delivery of a human ArgUGA tRNA to restore full-length hERG protein. The results demonstrate mutation-specific, context-agnostic PTC correction and elevate the therapeutic potential of this approach for rare genetic diseases caused by stop codons.

Oh my gut! Is the microbial origin of neurodegenerative diseases real?

There is no cure or effective treatment for neurodegenerative protein conformational diseases (PCDs), such as Alzheimer's or Parkinson's diseases, mainly because the etiology of these diseases remains elusive. Recent data suggest that unique changes in the gut microbial composition are associated with these ailments; however, our current understanding of the bacterial role in the pathogenesis of PCDs is hindered by the complexity of the microbial communities associated with specific microbiomes, such as the gut, oral, or vaginal microbiota. The composition of these specific microbiomes is regarded as a unique fingerprint affected by factors such as infections, diet, lifestyle, and antibiotics. All of these factors also affect the severity of neurodegenerative diseases. The majority of studies that reveal microbial contribution are correlational, and various models, including worm, fly, and mouse, are being utilized to decipher the role of individual microbes that may affect disease onset and progression. Recent evidence from across model organisms and humans shows a positive correlation between the presence of gram-negative enteropathogenic bacteria and the pathogenesis of PCDs. While these correlational studies do not provide a mechanistic explanation, they do reveal contributing bacterial species and provide an important basis for further investigation. One of the lurking concerns related to the microbial contribution to PCDs is the increasing prevalence of antibiotic resistance and poor antibiotic stewardship, which ultimately select for proteotoxic bacteria, especially the gram-negative species that are known for intrinsic resistance. In this review, we summarize what is known about individual microbial contribution to PCDs and the potential impact of increasing antimicrobial resistance.

In Silico Selection and Validation of High-Affinity ssDNA Aptamers Targeting Paromomycin

Glycans are promising for disease diagnosis since glycan biosynthesis is significantly affected by disease states, and glycosylation changes are probably more pronounced than protein expression during the transformation to the diseased condition. Glycan-specific aptamers can be developed for challenging applications such as cancer targeting; however, the high flexibility of glycosidic bonds and scarcity of studies on glycan-aptamer binding mechanisms increased the difficulty of screening. In this work, the model of interactions between glycans and ssDNA aptamers synthesized based on the sequence of rRNA genes was developed. Our simulation-based approach revealed that paromomycin as a representative example of glycans is preferred to bind base-restricted stem structures of aptamers because they are more critical in stabilizing the flexible structures of glycans. Combined experiments and simulations have identified two optimal mutant aptamers. Our work would provide a potential strategy that the glycan-binding rRNA genes could act as the initial aptamer pools to accelerate aptamer screening. In addition, this in silico workflow would be potentially applied in the more extensive in vitro development and application of RNA-templated ssDNA aptamers targeting glycans.

Decoding and Recoding of mRNA Sequences by the Ribosome

Faithful translation of messenger RNA (mRNA) into protein is essential to maintain protein homeostasis in the cell. Spontaneous translation errors are very rare due to stringent selection of cognate aminoacyl transfer RNAs (tRNAs) and the tight control of the mRNA reading frame by the ribosome. Recoding events, such as stop codon readthrough, frameshifting, and translational bypassing, reprogram the ribosome to make intentional mistakes and produce alternative proteins from the same mRNA. The hallmark of recoding is the change of ribosome dynamics. The signals for recoding are built into the mRNA, but their reading depends on the genetic makeup of the cell, resulting in cell-specific changes in expression programs. In this review, I discuss the mechanisms of canonical decoding and tRNA-mRNA translocation; describe alternative pathways leading to recoding; and identify the links among mRNA signals, ribosome dynamics, and recoding.

Streptothricin F is a bactericidal antibiotic effective against highly drug-resistant gram-negative bacteria that interacts with the 30S subunit of the 70S ribosome

The streptothricin natural product mixture (also known as nourseothricin) was discovered in the early 1940s, generating intense initial interest because of excellent gram-negative activity. Here, we establish the activity spectrum of nourseothricin and its main components, streptothricin F (S-F, 1 lysine) and streptothricin D (S-D, 3 lysines), purified to homogeneity, against highly drug-resistant, carbapenem-resistant Enterobacterales (CRE) and Acinetobacter baumannii. For CRE, the MIC50 and MIC90 for S-F and S-D were 2 and 4 μM, and 0.25 and 0.5 μM, respectively. S-F and nourseothricin showed rapid, bactericidal activity. S-F and S-D both showed approximately 40-fold greater selectivity for prokaryotic than eukaryotic ribosomes in in vitro translation assays. In vivo, delayed renal toxicity occurred at >10-fold higher doses of S-F compared with S-D. Substantial treatment effect of S-F in the murine thigh model was observed against the otherwise pandrug-resistant, NDM-1-expressing Klebsiella pneumoniae Nevada strain with minimal or no toxicity. Cryo-EM characterization of S-F bound to the A. baumannii 70S ribosome defines extensive hydrogen bonding of the S-F steptolidine moiety, as a guanine mimetic, to the 16S rRNA C1054 nucleobase (Escherichia coli numbering) in helix 34, and the carbamoylated gulosamine moiety of S-F with A1196, explaining the high-level resistance conferred by corresponding mutations at the residues identified in single rrn operon E. coli. Structural analysis suggests that S-F probes the A-decoding site, which potentially may account for its miscoding activity. Based on unique and promising activity, we suggest that the streptothricin scaffold deserves further preclinical exploration as a potential therapeutic for drug-resistant, gram-negative pathogens.

Emerging Personalized Opportunities for Enhancing Translational Readthrough in Rare Genetic Diseases and Beyond

Nonsense mutations trigger premature translation termination and often give rise to prevalent and rare genetic diseases. Consequently, the pharmacological suppression of an unscheduled stop codon represents an attractive treatment option and is of high clinical relevance. At the molecular level, the ability of the ribosome to continue translation past a stop codon is designated stop codon readthrough (SCR). SCR of disease-causing premature termination codons (PTCs) is minimal but small molecule interventions, such as treatment with aminoglycoside antibiotics, can enhance its frequency. In this review, we summarize the current understanding of translation termination (both at PTCs and at cognate stop codons) and highlight recently discovered pathways that influence its fidelity. We describe the mechanisms involved in the recognition and readthrough of PTCs and report on SCR-inducing compounds currently explored in preclinical research and clinical trials. We conclude by reviewing the ongoing attempts of personalized nonsense suppression therapy in different disease contexts, including the genetic skin condition epidermolysis bullosa.

Sustainable on-farm strategy for the disposal of antibiotic fermentation residue: Co-benefits for resource recovery and resistance mitigation

Antibiotic fermentation residue is a key issue for the sustainable operation of pharmaceutical companies, and its improper disposal may cause antibiotic resistance transfer in the environment. However, little is known about the resource recycling strategy of this pharmaceutical waste. Herein, we used hydrothermal spray-dried (HT+SD) and multi-plate dryer (MD) methods to produce bio-organic fertilizers and applied them to an internal recycling model of a field trial. The concentrations of antibiotics (penicillin, cephalosporin, and erythromycin) in the bio-fertilizer, wastewater, and exhaust gas were in the range of 0.002-0.68 mg/kg, ≤ 0.35 ng/mL, and 0.03-0.89 ng/mL, respectively. The organic matter and total nitrogen, phosphorus, and potassium contents were approximately 80% and 10%, respectively. The soil bacterial community was similar among the fertilizer treatments in the same crop cultivation. A total of 233 antibiotic resistance genes (ARGs) and 43 mobile genetic elements (MGEs) were detected, including seven Rank I ARGs and five Rank II ARGs. Random forest analysis showed that gene acc(3)-Via and plasmid trb-C were biomarkers, for which the resistance and the transfer mechanisms were antibiotic inactivation and conjugation, respectively. The results imply that AFR recycling disposal mode is a promising prospect for pharmaceutical waste management.

Translational Fidelity during Bacterial Stresses and Host Interactions

Translational fidelity refers to accuracy during protein synthesis and is maintained in all three domains of life. Translational errors occur at base levels during normal conditions and may rise due to mutations or stress conditions. In this article, we review our current understanding of how translational fidelity is perturbed by various environmental stresses that bacterial pathogens encounter during host interactions. We discuss how oxidative stress, metabolic stresses, and antibiotics affect various types of translational errors and the resulting effects on stress adaption and fitness. We also discuss the roles of translational fidelity during pathogen-host interactions and the underlying mechanisms. Many of the studies covered in this review will be based on work with Salmonella enterica and Escherichia coli, but other bacterial pathogens will also be discussed.

Bridging ribosomal synthesis to cell growth through the lens of kinetics

Understanding prokaryotic cell growth requires a multiscale modeling framework from the kinetics perspective. The detailed kinetics pathway of ribosomes exhibits features beyond the scope of the classical Hopfield kinetics model. The complexity of the molecular responses to various nutrient conditions poses additional challenge to elucidate the cell growth. Herein, a kinetics framework is developed to bridge ribosomal synthesis to cell growth. For the ribosomal synthesis kinetics, the competitive binding between cognate and near-cognate tRNAs for ribosomes can be modulated by Mg2+. This results in distinct patterns of the speed - accuracy relation comprising "trade-off" and "competition" regimes. Furthermore, the cell growth rate is optimized by varying the characteristics of ribosomal synthesis through cellular responses to different nutrient conditions. In this scenario, cellular responses to nutrient conditions manifest by two quadratic scaling relations: one for nutrient flux versus cell mass, the other for ribosomal number versus growth rate. Both are in quantitative agreement with experimental measurements.

Silver nanoparticles enhance the efficacy of aminoglycosides against antibiotic-resistant bacteria

As the threat of antimicrobial-resistant bacteria compromises the safety and efficacy of modern healthcare practices, the search for effective treatments is more urgent than ever. For centuries, silver (Ag) has been known to have antibacterial properties and, over the past two decades, Ag-based nanoparticles have gained traction as potential antimicrobials. The antibacterial efficacy of Ag varies with structure, size, and concentration. In the present study, we examined Ag nanoparticles (AgNPs) for their antimicrobial activity and safety. We compared different commercially-available AgNPs against gram-negative Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii, and gram-positive Staphylococcus aureus methicillin-resistant and susceptible strains. The most effective formula of AgNPs tested had single-digit (μg/mL) minimum inhibitory concentrations against gram-negative multidrug-resistant clinical bacterial isolates with novel and emerging mechanisms of resistance. The mode of killing was assessed in E. coli and was found to be bactericidal, which is consistent with previous studies using other AgNP formulations. We evaluated cytotoxicity by measuring physiological readouts using the Caenorhabditis elegans model and found that motility was affected, but not the lifespan. Furthermore, we found that at their antibacterial concentrations, AgNPs were non-cytotoxic to any of the mammalian cell lines tested, including macrophages, stem cells, and epithelial cells. More interestingly, our experiments revealed synergy with clinically relevant antibiotics. We found that a non-toxic and non-effective concentration of AgNPs reduced the minimum inhibitory concentrations of aminoglycoside by approximately 22-fold. Because both aminoglycosides and Ag are known to target the bacterial ribosome, we tested whether Ag could also target eukaryotic ribosomes. We measured the rate of mistranslation at bactericidal concentration and found no effect, indicating that AgNPs are not proteotoxic to the host at the tested concentrations. Collectively, our results suggest that AgNPs could have a promising clinical application as a potential stand-alone therapy or antibiotic adjuvants.

Ribosome biogenesis in disease: new players and therapeutic targets

The ribosome is a multi-unit complex that translates mRNA into protein. Ribosome biogenesis is the process that generates ribosomes and plays an essential role in cell proliferation, differentiation, apoptosis, development, and transformation. The mTORC1, Myc, and noncoding RNA signaling pathways are the primary mediators that work jointly with RNA polymerases and ribosome proteins to control ribosome biogenesis and protein synthesis. Activation of mTORC1 is required for normal fetal growth and development and tissue regeneration after birth. Myc is implicated in cancer development by enhancing RNA Pol II activity, leading to uncontrolled cancer cell growth. The deregulation of noncoding RNAs such as microRNAs, long noncoding RNAs, and circular RNAs is involved in developing blood, neurodegenerative diseases, and atherosclerosis. We review the similarities and differences between eukaryotic and bacterial ribosomes and the molecular mechanism of ribosome-targeting antibiotics and bacterial resistance. We also review the most recent findings of ribosome dysfunction in COVID-19 and other conditions and discuss the consequences of ribosome frameshifting, ribosome-stalling, and ribosome-collision. We summarize the role of ribosome biogenesis in the development of various diseases. Furthermore, we review the current clinical trials, prospective vaccines for COVID-19, and therapies targeting ribosome biogenesis in cancer, cardiovascular disease, aging, and neurodegenerative disease.

A mini-review: environmental and metabolic factors affecting aminoglycoside efficacy

Following the discovery of streptomycin from Streptomyces griseus in the 1940s by Selman Waksman and colleagues, aminoglycosides were first used to treat tuberculosis and then numerous derivatives have since been used to combat a wide variety of bacterial infections. These bactericidal antibiotics were used as first-line treatments for several decades but were largely replaced by ß-lactams and fluoroquinolones in the 1980s, although widespread emergence of antibiotic-resistance has led to renewed interest in aminoglycosides. The primary site of action for aminoglycosides is the 30 S ribosomal subunit where they disrupt protein translation, which contributes to widespread cellular damage through a number of secondary effects including rapid uptake of aminoglycosides via elevated proton-motive force (PMF), membrane damage and breakdown, oxidative stress, and hyperpolarisation of the membrane. Several factors associated with aminoglycoside entry have been shown to impact upon bacterial killing, and more recent work has revealed a complex relationship between metabolic states and the efficacy of different aminoglycosides. Hence, it is imperative to consider the environmental conditions and bacterial physiology and how this can impact upon aminoglycoside entry and potency. This mini-review seeks to discuss recent advances in this area and how this might affect the future use of aminoglycosides.

Microbe-mediated activation of indoxacarb in German cockroach (Blattella germanica L.)

The German cockroach (Blattella germanica L.) is a major urban pest worldwide and is notorious for its ability to detoxify and resist insecticides. German cockroaches have generalist feeding habits that expose them to a range of potential hazardous substances and host a wide variety of unique microbial species, which may potentially facilitate unique detoxification capabilities. Since field German cockroach populations are routinely exposed to both bait and spray insecticide treatments, we hypothesized whether these unique gut microbes might play roles in toxicological processes of the host insect. The goals of this research were to understand the metabolic processes inside the German cockroach gut after treatment with kanamycin, a broad-ranging antibiotic, and indoxacarb, an oxadiazine pro-insecticide used in cockroach bait products. In these experiments, two resistant cockroach strains were obtained from field populations in Danville, IL and compared to a susceptible laboratory strain that had no previous exposure to insecticides (J-wax). Roaches provided kanamycin-infused water had lower median mortality to indoxacarb compared to the control treatment in feeding bioassays regardless of strain, but in vial (surface contact) bioassays, only susceptible cockroaches experienced a shift in mortality apparently due to their greater susceptibility. When frass extracts of indoxacarb-fed cockroaches were analyzed, less of the active, hydrolytic metabolite DCJW (N-decarbomethoxyllated JW062) was produced relative to the parent compound indoxacarb with the antibiotic KAN. This result was further corroborated by hydrolase activity assays of whole homogenized cockroach guts. Taken together these results provide novel evidence of microbe-mediated pro-insecticide activation in the cockroach gut.

Phenotypic mutations contribute to protein diversity and shape protein evolution

Errors in DNA replication generate genetic mutations, while errors in transcription and translation lead to phenotypic mutations. Phenotypic mutations are orders of magnitude more frequent than genetic ones, yet they are less understood. Here, we review the types of phenotypic mutations, their quantifications, and their role in protein evolution and disease. The diversity generated by phenotypic mutation can facilitate adaptive evolution. Indeed, phenotypic mutations, such as ribosomal frameshift and stop codon readthrough, sometimes serve to regulate protein expression and function. Phenotypic mutations have often been linked to fitness decrease and diseases. Thus, understanding the protein heterogeneity and phenotypic diversity caused by phenotypic mutations will advance our understanding of protein evolution and have implications on human health and diseases.

Multi-omics analysis reveals the influence of tetracycline on the growth of ryegrass root

Environmental factors, including antibiotics such as tetracycline, can alter biological processes in plants. To ascertain how cell/tissue response to tetracycline, a multi-omic analysis was implemented to explore the molecular mechanism of tetracycline influencing the growth of ryegrass root. Tetracycline induced extensive changes in the root metabolome in plants, particularly impacting metabolites of flavonoid metabolic pathways, which were supported through consistent differences between transcriptome and proteome. Cross-comparison between mRNA and protein contents considered the authentication of congruence with related metabolites and revealed changes of several biological processes under tetracycline stress. Overall, we present an undemanding multi-omic strategy to survey the significant influence on the root under tetracycline stress.

Proteomics Study of the Synergistic Killing of Tigecycline in Combination With Aminoglycosides Against Carbapenem-Resistant Klebsiella pneumoniae

Co-administration of antibiotics with synergistic effects is one method to combat carbapenem-resistant organisms. Although the synergistic effects of tigecycline combined with aminoglycosides against carbapenem-resistant Klebsiella pneumoniae (CRKP) have been demonstrated in vitro and in animal models, the underlying mechanism remains elusive. Here we used proteomics analysis to assess the short-term bacterial responses to tigecycline and aminoglycosides alone or in combination. Emergence of tigecycline resistance during treatment and the susceptibility of tigecycline-resistant strains to aminoglycosides was further evaluated. The proteomic responses to tigecycline and aminoglycosides were divergent in monotherapy, with proteomic alterations to combination therapy dominated by tigecycline. Adaptive responses to tigecycline were associated with the upregulation of oxidative phosphorylation and translation-related proteins. These responses might confer CRKP hypersensitivity towards aminoglycosides by increasing the drug uptake and binding targets. Meanwhile, tigecycline might perturb adaptive responses to aminoglycosides through inhibition of heat shock response. Tigecycline-resistant strains could be isolated within 24 h exposure even in strains without heteroresistance, and the sensitivity to aminoglycosides significantly increased in resistant strains. Overall, these findings demonstrated that adaption to tigecycline in CRKP was a double-edged sword associated with the synergistic killing in tigecycline–aminoglycoside combination. Evolutionary hypersensitivity can provide novel insight into the mechanisms of antibiotic synergistic effects.

Comparative genomics analysis and virulence-related factors in novel Aliarcobacter faecis and Aliarcobacter lanthieri species identified as potential opportunistic pathogens

Background

Emerging pathogenic bacteria are an increasing threat to public health. Two recently described species of the genus Aliarcobacter, A. faecis and A. lanthieri, isolated from human or livestock feces, are closely related to Aliarcobacter zoonotic pathogens (A. cryaerophilus, A. skirrowii, and A. butzleri). In this study, comparative genomics analysis was carried out to examine the virulence-related, including virulence, antibiotic, and toxin (VAT) factors in the reference strains of A. faecis and A. lanthieri that may enable them to become potentially opportunistic zoonotic pathogens.

Results

Our results showed that the genomes of the reference strains of both species have flagella genes (flaA, flaB, flgG, flhA, flhB, fliI, fliP, motA and cheY1) as motility and export apparatus, as well as genes encoding the Twin-arginine translocation (Tat) (tatA, tatB and tatC), type II (pulE and pulF) and III (fliF, fliN and ylqH) secretory pathways, allowing them to secrete proteins into the periplasm and host cells. Invasion and immune evasion genes (ciaB, iamA, mviN, pldA, irgA and fur2) are found in both species, while adherence genes (cadF and cj1349) are only found in A. lanthieri. Acid (clpB), heat (clpA and clpB), osmotic (mviN), and low-iron (irgA and fur2) stress resistance genes were observed in both species, although urease genes were not found in them. In addition, arcB, gyrA and gyrB were found in both species, mutations of which may mediate the resistance to quaternary ammonium compounds (QACs). Furthermore, 11 VAT genes including six virulence (cadF, ciaB, irgA, mviN, pldA, and tlyA), two antibiotic resistance [tet(O) and tet(W)] and three cytolethal distending toxin (cdtA, cdtB, and cdtC) genes were validated with the PCR assays. A. lanthieri tested positive for all 11 VAT genes. By contrast, A. faecis showed positive for ten genes except for cdtB because no PCR assay for this gene was available for this species.

Conclusions

The identification of the virulence, antibiotic-resistance, and toxin genes in the genomes of A. faecis and A. lanthieri reference strains through comparative genomics analysis and PCR assays highlighted the potential zoonotic pathogenicity of these two species. However, it is necessary to extend this study to include more clinical and environmental strains to explore inter-species and strain-level genetic variations in virulence-related genes and assess their potential to be opportunistic pathogens for animals and humans.

Physiological Responses of Ribosomal Protein S12 K43 Mutants of Corynebacterium glutamicum

Bacterial resistance to streptomycin is often acquired as a consequence of mutations in rpsL, the gene encoding ribosomal protein S12. Corynebacterium glutamicum is a non-pathogenic Gram-positive soil bacterium that has been widely used in industry. In a previous study, we screened several streptomycin-resistant rpsL K43 mutants of C. glutamicum, and surprisingly found that two of them also confer chloramphenicol and/or kanamycin resistance. In order to understand whether or not a single mutation of rpsL^K43 could confer resistance to multiple antibiotics, in this study we attempted to construct saturation mutagenesis of rpsL K43 by rational genetic manipulation. Despite many efforts had been made, only nine mutants were successfully constructed. They were indeed resistant to streptomycin, but not to other antibiotics. This suggested that other mutations should be acquired, contributing to multiple antibiotics in the screened strains. The growth and enhanced green fluorescent protein (eGFP) expression of these nine mutants were then investigated. The results showed that they grew differently in CGXII minimal medium, but not in BHI medium. When cultured in the absence of streptomycin, the expression of eGFP was positively proportional to the growth, approximately, while in the presence of streptomycin, the expression of eGFP was proportional to the ability of streptomycin resistance.

Potential Effect of Post-Transcriptional Substitutions of Tyrosine for Cysteine Residues on Transformation of Amyloidogenic Proteins

The review considers the reasons and consequences of post-transcriptional tyrosine substitutions for cysteine residues. Main attention is paid to the Tyr/Cys substitutions that arise during gene expression in bacterial systems at the stage of protein translation as a result of misrecognition of the similar mRNA codons. Notably, translation errors generally occur relatively rarely - from 10^-4 to 10^-3 errors per codon for E. coli cells, but in some cases the error rate increases significantly. For example, this is typical for certain pairs of codons, when the culture conditions change or in the presence of antibiotics. Thus, with overproduction of the recombinant human alpha-synuclein in E. coli cells, the content of the mutant form with the replacement of Tyr136 (UAC codon) with a cysteine residue (UGC codon) can reach 50%. Possible reasons for the increased production of alpha-synuclein with the Tyr136Cys substitution are considered, as well as consequences of the presence of mutant forms in preparations of amyloidogenic proteins when studying their pathological transformation in vitro. A separate section is devoted to the Tyr/Cys substitutions occurring due to mRNA editing by adenosine deaminases, which is typical for eukaryotic organisms, and the possible role of this process in the amyloid transformation of proteins associated with neurodegenerative diseases.

Structural mechanism of GTPase-powered ribosome-tRNA movement

GTPases are regulators of cell signaling acting as molecular switches. The translational GTPase EF-G stands out, as it uses GTP hydrolysis to generate force and promote the movement of the ribosome along the mRNA. The key unresolved question is how GTP hydrolysis drives molecular movement. Here, we visualize the GTPase-powered step of ongoing translocation by time-resolved cryo-EM. EF-G in the active GDP-Pi form stabilizes the rotated conformation of ribosomal subunits and induces twisting of the sarcin-ricin loop of the 23 S rRNA. Refolding of the GTPase switch regions upon Pi release initiates a large-scale rigid-body rotation of EF-G pivoting around the sarcin-ricin loop that facilitates back rotation of the ribosomal subunits and forward swiveling of the head domain of the small subunit, ultimately driving tRNA forward movement. The findings demonstrate how a GTPase orchestrates spontaneous thermal fluctuations of a large RNA-protein complex into force-generating molecular movement.

Deficiency in cytosine DNA methylation leads to high chaperonin expression and tolerance to aminoglycosides in Vibrio cholerae

Antibiotic resistance has become a major global issue. Understanding the molecular mechanisms underlying microbial adaptation to antibiotics is of keen importance to fight Antimicrobial Resistance (AMR). Aminoglycosides are a class of antibiotics that target the small subunit of the bacterial ribosome, disrupting translational fidelity and increasing the levels of misfolded proteins in the cell. In this work, we investigated the role of VchM, a DNA methyltransferase, in the response of the human pathogen Vibrio cholerae to aminoglycosides. VchM is a V. cholerae specific orphan m5C DNA methyltransferase that generates cytosine methylation at 5'-RCCGGY-3' motifs. We show that deletion of vchM, although causing a growth defect in absence of stress, allows V. cholerae cells to cope with aminoglycoside stress at both sub-lethal and lethal concentrations of these antibiotics. Through transcriptomic and genetic approaches, we show that groESL-2 (a specific set of chaperonin-encoding genes located on the second chromosome of V. cholerae), are upregulated in cells lacking vchM and are needed for the tolerance of vchM mutant to lethal aminoglycoside treatment, likely by fighting aminoglycoside-induced misfolded proteins. Interestingly, preventing VchM methylation of the four RCCGGY sites located in groESL-2 region, leads to a higher expression of these genes in WT cells, showing that the expression of these chaperonins is modulated in V. cholerae by DNA methylation.

An Unnatural Amino Acid-Regulated Growth Controller Based on Informational Disturbance

We designed a novel growth controller regulated by feeding of an unnatural amino acid, N^ε-benzyloxycarbonyl-l-lysine (ZK), using a specific incorporation system at a sense codon. This system is constructed by a pair of modified pyrrolisyl-tRNA synthetase (PylRS) and its cognate tRNA (tRNA^pyl). Although ZK is non-toxic for normal organisms, the growth of Escherichia coli carrying the ZK incorporation system was inhibited in a ZK concentration-dependent manner without causing rapid bacterial death, presumably due to generation of non-functional or toxic proteins. The extent of growth inhibition strongly depended on the anticodon sequence of the tRNA^pyl gene. Taking advantage of the low selectivity of PylRS for tRNA^pyl anticodons, we experimentally determined the most effective anticodon sequence among all 64 nucleotide sequences in the anticodon region of tRNA^pyl gene. The results suggest that the ZK-regulated growth controller is a simple, target-specific, environmental noise-resistant and titratable system. This technique may be applicable to a wide variety of organisms because the growth inhibitory effects are caused by "informational disturbance", in which the highly conserved system for transmission of information from DNA to proteins is perturbed.

Mechanistic insights into translation inhibition by aminoglycoside antibiotic arbekacin

How aminoglycoside antibiotics limit bacterial growth and viability is not clearly understood. Here we employ fast kinetics to reveal the molecular mechanism of action of a clinically used, new-generation, semisynthetic aminoglycoside Arbekacin (ABK), which is designed to avoid enzyme-mediated deactivation common to other aminoglycosides. Our results portray complete picture of ABK inhibition of bacterial translation with precise quantitative characterizations. We find that ABK inhibits different steps of translation in nanomolar to micromolar concentrations by imparting pleotropic effects. ABK binding stalls elongating ribosomes to a state, which is unfavorable for EF-G binding. This prolongs individual translocation step from ∼50 ms to at least 2 s; the mean time of translocation increases inversely with EF-G concentration. ABK also inhibits translation termination by obstructing RF1/RF2 binding to the ribosome. Furthermore, ABK decreases accuracy of mRNA decoding (UUC vs. CUC) by ∼80 000 fold, causing aberrant protein production. Importantly, translocation and termination events cannot be completely stopped even with high ABK concentration. Extrapolating our kinetic model of ABK action, we postulate that aminoglycosides impose bacteriostatic effect mainly by inhibiting translocation, while they become bactericidal in combination with decoding errors.

Bacterial RF3 senses chaperone function in co-translational folding

Molecular chaperones assist with protein folding by interacting with nascent polypeptide chains (NCs) during translation. Whether the ribosome can sense chaperone defects and, in response, abort translation of misfolding NCs has not yet been explored. Here we used quantitative proteomics to investigate the ribosome-associated chaperone network in E. coli and the consequences of its dysfunction. Trigger factor and the DnaK (Hsp70) system are the major NC-binding chaperones. HtpG (Hsp90), GroEL, and ClpB contribute increasingly when DnaK is deficient. Surprisingly, misfolding because of defects in co-translational chaperone function or amino acid analog incorporation results in recruitment of the non-canonical release factor RF3. RF3 recognizes aberrant NCs and then moves to the peptidyltransferase site to cooperate with RF2 in mediating chain termination, facilitating clearance by degradation. This function of RF3 reduces the accumulation of misfolded proteins and is critical for proteostasis maintenance and cell survival under conditions of limited chaperone availability.