A Novel Mechanism of Programmed Cell Death in Bacteria by Toxin–Antitoxin Systems Corrupts Peptidoglycan Synthesis

Most genomes of bacteria contain toxin–antitoxin (TA) systems. These gene systems encode a toxic protein and its cognate antitoxin. Upon antitoxin degradation, the toxin induces cell stasis or death. TA systems have been linked with numerous functions, including growth modulation, genome maintenance, and stress response. Members of the epsilon/zeta TA family are found throughout the genomes of pathogenic bacteria and were shown not only to stabilize resistance plasmids but also to promote virulence. The broad distribution of epsilon/zeta systems implies that zeta toxins utilize a ubiquitous bacteriotoxic mechanism. However, whereas all other TA families known to date poison macromolecules involved in translation or replication, the target of zeta toxins remained inscrutable. We used in vivo techniques such as microscropy and permeability assays to show that pneumococcal zeta toxin PezT impairs cell wall synthesis and triggers autolysis in Escherichia coli. Subsequently, we demonstrated in vitro that zeta toxins in general phosphorylate the ubiquitous peptidoglycan precursor uridine diphosphate-N-acetylglucosamine (UNAG) and that this activity is counteracted by binding of antitoxin. After identification of the product we verified the kinase activity in vivo by analyzing metabolite extracts of cells poisoned by PezT using high pressure liquid chromatograpy (HPLC). We further show that phosphorylated UNAG inhibitis MurA, the enzyme catalyzing the initial step in bacterial peptidoglycan biosynthesis. Additionally, we provide what is to our knowledge the first crystal structure of a zeta toxin bound to its substrate. We show that zeta toxins are novel kinases that poison bacteria through global inhibition of peptidoglycan synthesis. This provides a fundamental understanding of how epsilon/zeta TA systems stabilize mobile genetic elements. Additionally, our results imply a mechanism that connects activity of zeta toxin PezT to virulence of pneumococcal infections. Finally, we discuss how phosphorylated UNAG likely poisons additional pathways of bacterial cell wall synthesis, making it an attractive lead compound for development of new antibiotics

Does a “Western Lifestyle” Confer a Higher Burden of Colorectal Cancer? A Comparison of EU15+ Countries versus Global Trends between 1990 and 2019

The incidence of colorectal cancer (CRC) in the U.S. is declining in adults 50 years and older; however, recent studies suggest an increasing disease burden among adults under age 50. This study aims to compare the incidence, mortality, and mortality-to-incidence ratios (MIRs) of CRC in EU15+ countries to determine if similar age-stratified occurrences are observed across these countries with similar “Western lifestyle”-related risk factors. Incidence and mortality rates for CRC between 1990 and 2019 were extracted using the Global Burden of Disease database. The data were age-stratified into groups between ages 25–49, 50–69, and greater than 69 years. We observed that the incidence of CRC increased globally for all age groups, with the highest increase observed for males (75.9%) and females (27.7%) aged 25–49. A similar trend was observed in 15 of the 19 EU15+ countries for males and 16 of the 19 EU15+ countries for females aged 25–49. Global mortality rates decreased for all age groups in females but increased for males in all age groups. This raises concerns regarding potentially modifiable risk factors contributing to increased CRC development and underscores the importance of implementing standardized screening at an earlier stage to ensure adequate detection in the younger population