Oxidative stress drives mutagenesis through transcription-coupled repair in bacteria

Application and research progress of ARTP mutagenesis in actinomycetes breeding

Atmospheric and room temperature plasma (ARTP) is an emerging artificial mutagenesis breeding technology. In comparison to traditional physical and chemical methods, ARTP technology can induce DNA damage more effectively and obtain mutation strains with stable heredity more easily after screening. It possesses advantages such as simplicity, safety, non-toxicity, and cost-effectiveness, showing high application value in microbial breeding. This article focuses on ARTP mutagenesis breeding of actinomycetes, specifically highlighting the application of ARTP mutagenesis technology in improving the performance of strains and enhancing the biosynthetic capabilities of actinomycetes. We analyzed the advantages and challenges of ARTP technology in actinomycetes breeding and summarized the common features, specific mutation sites and metabolic pathways of ARTP mutagenic strains, which could give guidance for genetic modification. It suggested that the future research work should focus on the establishment of high throughput rapid screening methods and integrate transcriptomics, proteomics, metabonomics and other omics to delve into the genetic regulations and synthetic mechanisms of the bioactive substances in ARTP mutated actinomycetes. This article aims to provide new perspectives for actinomycetes breeding through the establishment and application of ARTP mutagenesis technology, thereby promoting source innovation and the sustainable industrial development of actinomycetes.

RNA polymerase stalling-derived genome instability underlies ribosomal antibiotic efficacy and resistance evolution

Bacteria often evolve antibiotic resistance through mutagenesis. However, the processes causing the mutagenesis have not been fully resolved. Here, we find that a broad range of ribosome-targeting antibiotics cause mutations through an underexplored pathway. Focusing on the clinically important aminoglycoside gentamicin, we find that the translation inhibitor causes genome-wide premature stalling of RNA polymerase (RNAP) in a loci-dependent manner. Further analysis shows that the stalling is caused by the disruption of transcription-translation coupling. Anti-intuitively, the stalled RNAPs subsequently induce lesions to the DNA via transcription-coupled repair. While most of the bacteria are killed by genotoxicity, a small subpopulation acquires mutations via SOS-induced mutagenesis. Given that these processes are triggered shortly after antibiotic addition, resistance rapidly emerges in the population. Our work reveals a mechanism of action of ribosomal antibiotics, illustrates the importance of dissecting the complex interplay between multiple molecular processes in understanding antibiotic efficacy, and suggests new strategies for countering the development of resistance.

Bioenergetic stress potentiates antimicrobial resistance and persistence

Antimicrobial resistance (AMR) is a global health crisis and there is an urgent need to better understand AMR mechanisms. Antibiotic treatment alters several aspects of bacterial physiology, including increased ATP utilization, carbon metabolism, and reactive oxygen species (ROS) formation. However, how the "bioenergetic stress" induced by increased ATP utilization affects treatment outcomes is unknown. Here we utilized a synthetic biology approach to study the direct effects of bioenergetic stress on antibiotic efficacy. We engineered a genetic system that constitutively hydrolyzes ATP or NADH in Escherichia coli. We found that bioenergetic stress potentiates AMR evolution via enhanced ROS production, mutagenic break repair, and transcription-coupled repair. We also find that bioenergetic stress potentiates antimicrobial persistence via potentiated stringent response activation. We propose a unifying model that antibiotic-induced antimicrobial resistance and persistence is caused by antibiotic-induced. This has important implications for preventing or curbing the spread of AMR infections.

Oxidative stress responses in biofilms

Oxidizing agents are low-molecular-weight molecules that oxidize other substances by accepting electrons from them. They include reactive oxygen species (ROS), such as superoxide anions (O2-), hydrogen peroxide (H2O2), and hydroxyl radicals (HO-), and reactive chlorine species (RCS) including sodium hypochlorite (NaOCl) and its active ingredient hypochlorous acid (HOCl), and chloramines. Bacteria encounter oxidizing agents in many different environments and from diverse sources. Among them, they can be produced endogenously by aerobic respiration or exogenously by the use of disinfectants and cleaning agents, as well as by the mammalian immune system. Furthermore, human activities like industrial effluent pollution, agricultural runoff, and environmental activities like volcanic eruptions and photosynthesis are also sources of oxidants. Despite their antimicrobial effects, bacteria have developed many mechanisms to resist the damage caused by these toxic molecules. Previous research has demonstrated that growing as a biofilm particularly enhances bacterial survival against oxidizing agents. This review aims to summarize the current knowledge on the resistance mechanisms employed by bacterial biofilms against ROS and RCS, focussing on the most important mechanisms, including the formation of biofilms in response to oxidative stressors, the biofilm matrix as a protective barrier, the importance of detoxifying enzymes, and increased protection within multi-species biofilm communities. Understanding the complexity of bacterial responses against oxidative stress will provide valuable insights for potential therapeutic interventions and biofilm control strategies in diverse bacterial species.

Strand-resolved mutagenicity of DNA damage and repair

DNA base damage is a major source of oncogenic mutations1. Such damage can produce strand-phased mutation patterns and multiallelic variation through the process of lesion segregation2. Here we exploited these properties to reveal how strand-asymmetric processes, such as replication and transcription, shape DNA damage and repair. Despite distinct mechanisms of leading and lagging strand replication3,4, we observe identical fidelity and damage tolerance for both strands. For small alkylation adducts of DNA, our results support a model in which the same translesion polymerase is recruited on-the-fly to both replication strands, starkly contrasting the strand asymmetric tolerance of bulky UV-induced adducts5. The accumulation of multiple distinct mutations at the site of persistent lesions provides the means to quantify the relative efficiency of repair processes genome wide and at single-base resolution. At multiple scales, we show DNA damage-induced mutations are largely shaped by the influence of DNA accessibility on repair efficiency, rather than gradients of DNA damage. Finally, we reveal specific genomic conditions that can actively drive oncogenic mutagenesis by corrupting the fidelity of nucleotide excision repair. These results provide insight into how strand-asymmetric mechanisms underlie the formation, tolerance and repair of DNA damage, thereby shaping cancer genome evolution.

Relevance of the Adjuvant Effect between Cellular Homeostasis and Resistance to Antibiotics in Gram-Negative Bacteria with Pathogenic Capacity: A Study of Klebsiella pneumoniae

Antibiotic resistance has become a global issue. The most significant risk is the acquisition of these mechanisms by pathogenic bacteria, which can have a severe clinical impact and pose a public health risk. This problem assumes that bacterial fitness is a constant phenomenon and should be approached from an evolutionary perspective to develop the most appropriate and effective strategies to contain the emergence of strains with pathogenic potential. Resistance mechanisms can be understood as adaptive processes to stressful conditions. This review examines the relevance of homeostatic regulatory mechanisms in antimicrobial resistance mechanisms. We focus on the interactions in the cellular physiology of pathogenic bacteria, particularly Gram-negative bacteria, and specifically Klebsiella pneumoniae. From a clinical research perspective, understanding these interactions is crucial for comprehensively understanding the phenomenon of resistance and developing more effective drugs and treatments to limit or attenuate bacterial sepsis, since the most conserved adjuvant phenomena in bacterial physiology has turned out to be more optimized and, therefore, more susceptible to alterations due to pharmacological action.

Pathogenic bacteria experience pervasive RNA polymerase backtracking during infection

IMPORTANCE

Eukaryotic hosts have defense mechanisms that may disrupt molecular transactions along the pathogen's chromosome through excessive DNA damage. Given that DNA damage stalls RNA polymerase (RNAP) thereby increasing mutagenesis, investigating how host defense mechanisms impact the movement of the transcription machinery on the pathogen chromosome is crucial. Using a new methodology we developed, we elucidated the dynamics of RNAP movement and association with the chromosome in the pathogenic bacterium Salmonella enterica during infection. We found that dynamics of RNAP movement on the chromosome change significantly during infection genome-wide, including at regions that encode for key virulence genes. In particular, we found that there is pervasive RNAP backtracking on the bacterial chromosome during infections and that anti-backtracking factors are critical for pathogenesis. Altogether, our results suggest that, interestingly, the host environment can promote the development of antimicrobial resistance and hypervirulence as stalled RNAPs can accelerate evolution through increased mutagenesis.

A small molecule that inhibits the evolution of antibiotic resistance

Antibiotic resistance rapidly develops against almost all available therapeutics. Therefore, searching for new antibiotics to overcome the problem of antibiotic resistance alone is insufficient. Given that antibiotic resistance can be driven by mutagenesis, an avenue for preventing it is the inhibition of mutagenic processes. We previously showed that the DNA translocase Mfd is mutagenic and accelerates antibiotic resistance development. Here, we present our discovery of a small molecule that inhibits Mfd-dependent mutagenesis, ARM-1 (anti-resistance molecule 1). We found ARM-1 using a high-throughput, small molecule, in vivo screen. Using biochemical assays, we characterized the mechanism by which ARM-1 inhibits Mfd. Critically, we found that ARM-1 reduces mutagenesis and significantly delays antibiotic resistance development across highly divergent bacterial pathogens. These results demonstrate that the mutagenic proteins accelerating evolution can be directly inhibited. Furthermore, our findings suggest that Mfd inhibition, alongside antibiotics, is a potentially effective approach for prevention of antibiotic resistance development during treatment of infections.

Functional groups matter: metabolomics analysis of Escherichia coli exposed to trans-cinnamic acid and its derivatives unveils common and unique targets

Phenolic acids are derivatives of benzoic and cinnamic acids, which possess important biological activities at certain concentrations. Trans-cinnamic acid (t-CA) and its derivatives, such as p-coumaric acid (p-CA) and ferulic acid (FA) have been shown to have antibacterial activity against various Gram-positive and -negative bacteria. However, there is limited information available concerning the antibacterial mode of action of these phenolic acids. In this study, we aimed to ascertain metabolic alterations associated with exposure to t-CA, p-CA, and FA in Escherichia coli BW25113 using a nuclear magnetic resonance (NMR)-based metabolomics approach. The results showed that t-CA, p-CA, and FA treatments led to significant changes (p < 0.05) in the concentration of 42, 55, and 74% of the identified metabolites in E. coli, respectively. Partial least-squares discriminant analysis (PLS-DA) revealed a clear separation between control and phenolic acid groups with regard to metabolic response. Moreover, it was found that FA and p-CA treatment groups were clustered closely together but separated from the t-CA treatment group. Arginine, putrescine, cadaverine, galactose, and sucrose had the greatest impact on group differentiation. Quantitative pathway analysis demonstrated that arginine and proline, pyrimidine, glutathione, and galactose metabolisms, as well as aminoacyl-tRNA and arginine biosyntheses, were markedly affected by all phenolic acids. Finally, the H2O2 content of E. coli cells was significantly increased in response to t-CA and p-CA whereas all phenolic acids caused a dramatic increase in the number of apurinic/apyrimidinic sites. Overall, this study suggests that the metabolic response of E. coli cells to t-CA is relatively different from that to p-CA and FA. However, all phenolic acids had a certain impact on oxidative/antioxidant status, genomic stability, arginine-related pathways, and nucleic acid metabolism.

Anti-microbial resistance and aging-A design for evolution

The emergence of resistance to anti-infective agents poses a significant threat to successfully treating infections caused by bacteria. Bacteria acquire random mutations due to exposure to environmental stresses, which may increase their fitness to other selection pressures. Interestingly, for bacteria, the frequency of anti-microbial resistance (AMR) seems to be increasing in tandem with the human lifespan. Based on evidence from previous literature, we speculate that increased levels of free radicals (Reactive Oxygen Species-ROS and Reactive Nitrosative Species-RNS), elevated inflammation, and the altered tissue microenvironment in aged individuals may drive pathogen mutagenesis. If these mutations result in the hyperactivation of efflux pumps or alteration in drug target binding sites, it could confer AMR, thus rendering antibiotic therapy ineffective while leading to the selection of novel drug-resistant variants. This article is categorized under: Immune System Diseases > Genetics/Genomics/Epigenetics Infectious Diseases > Environmental Factors Metabolic Diseases > Environmental Factors.

Reactive oxidant species induced by antifungal drugs: identity, origins, functions, and connection to stress-induced cell death

Reactive oxidant species (ROS) are unstable, highly reactive molecules that are produced by cells either as byproducts of metabolism or synthesized by specialized enzymes. ROS can be detrimental, e.g., by damaging cellular macromolecules, or beneficial, e.g., by participating in signaling. An increasing body of evidence shows that various fungal species, including both yeasts and molds, increase ROS production upon exposure to the antifungal drugs currently used in the clinic: azoles, polyenes, and echinocandins. However, the implications of these findings are still largely unclear due to gaps in knowledge regarding the chemical nature, molecular origins, and functional consequences of these ROS. Because the detection of ROS in fungal cells has largely relied on fluorescent probes that lack specificity, the chemical nature of the ROS is not known, and it may vary depending on the specific fungus-drug combination. In several instances, the origin of antifungal drug-induced ROS has been identified as the mitochondria, but further experiments are necessary to strengthen this conclusion and to investigate other potential cellular ROS sources, such as the ER, peroxisomes, and ROS-producing enzymes. With respect to the function of the ROS, several studies have shown that they contribute to the drugs' fungicidal activities and may be part of drug-induced programmed cell death (PCD). However, whether these "pro-death" ROS are a primary consequence of the antifungal mechanism of action or a secondary consequence of drug-induced PCD remains unclear. Finally, several recent studies have raised the possibility that ROS induction can serve an adaptive role, promoting antifungal drug tolerance and the evolution of drug resistance. Filling these gaps in knowledge will reveal a new aspect of fungal biology and may identify new ways to potentiate antifungal drug activity or prevent the evolution of antifungal drug resistance.

Transcription-coupled global genomic repair in E. coli

The nucleotide excision repair (NER) pathway removes helix-distorting lesions from DNA in all organisms. Escherichia coli has long been a model for understanding NER, which is traditionally divided into major and minor subpathways known as global genome repair (GGR) and transcription-coupled repair (TCR), respectively. TCR has been assumed to be mediated exclusively by Mfd, a DNA translocase of minimal NER phenotype. This review summarizes the evidence that shaped the traditional view of NER in bacteria, and reviews data supporting a new model in which GGR and TCR are inseparable. In this new model, RNA polymerase serves both as the essential primary sensor of bulky DNA lesions genome-wide and as the delivery platform for the assembly of functional NER complexes in living cells.