Contribution of SOS genes to H2O2-induced apoptosis-like death in Escherichia coli

Identification of a novel NADPH generation reaction in the pentose phosphate pathway in Escherichia coli using mBFP

NADPH is a redox cofactor that drives the anabolic reactions. Although major NADPH generation reactions have been identified in Escherichia coli, some minor reactions have not been identified. In the present study, we explored novel NADPH generation reactions by monitoring the fluorescence dynamics after the addition of carbon sources to starved cells, using a metagenome-derived blue fluorescent protein (mBFP) as an intracellular NADPH reporter. Perturbation analyses were performed on a glucose-6-phosphate isomerase (PGI) deletion strain and its parental strain. Interestingly, mBFP fluorescence increased not only in the parental strain but also in the ΔPGI strain after the addition of xylose. Because the ΔPGI strain cannot metabolize xylose through the oxidative pentose phosphate pathway, this suggests that an unexpected NADPH generation reaction contributes to an increase in fluorescence. To unravel this mystery, we deleted the NADPH generation enzymes including transhydrogenase, isocitrate dehydrogenase, NADP+-dependent malic enzyme, glucose-6-phosphate dehydrogenase (G6PDH), and 6-phosphogluconate dehydrogenase (6PGDH) in the ΔPGI strain, and revealed that G6PDH and 6PGDH contribute to an increase in fluorescence under xylose conditions. In vitro assays using purified enzymes showed that G6PDH can produce NADPH using erythrose-4-phosphate (E4P) as a substitute for glucose-6-phosphate. Because the Km (0.65 mM) for E4P was much higher than the reported intracellular E4P concentrations in E. coli, little E4P must be metabolized through this bypass in the parental strain. However, the flux would increase when E4P accumulates in the cells owing to genetic modifications. This finding provides a metabolic engineering strategy for generating NADPH to produce useful compounds using xylose as a carbon source.IMPORTANCEBecause NADPH is consumed during the synthesis of various useful compounds, enhancing NADPH regeneration is highly desirable in metabolic engineering. In this study, we explored novel NADPH generation reactions in Escherichia coli using a fluorescent NADPH reporter and found that glucose-6-phosphate dehydrogenase can produce NADPH using erythrose-4-phosphate as a substrate under xylose conditions. Xylose is an abundant sugar in nature and is an attractive carbon source for bioproduction. Therefore, this finding contributes to novel pathway engineering strategies using a xylose carbon source in E. coli to produce useful compounds that consume NADPH for their synthesis.

Recent advances on environmental behavior of Cu-based nanomaterials in soil-plant system: A review

In recent years, copper-based nanomaterials (Cu-based NMs) have shown great potential in promoting agriculture development due to their special physicochemical characteristics. With the mass production and overuse of Cu-based NMs, there are potential effects on the soil-plant environment. Soil organisms, especially soil microorganisms, play a significant part in terrestrial or soil ecosystems; plants, as indirect organisms with soil-related Cu-based NMs, may affect human health through plant agricultural products. Understanding the accumulation and transformation of Cu-based NMs in soil-plant systems, as well as their ecotoxicological effects and potential mechanisms, is a prerequisite for the scientific assessment of environmental risks and safe application. Therefore, based on the current literature, this review: (i) introduces the accumulation and transformation behaviors of Cu-based NMs in soil and plant systems; (ii) focuses on the ecotoxicological effects of Cu-based NMs on a variety of organisms (microorganisms, invertebrates, and plants); (iii) reveals their corresponding toxicity mechanisms. It appears from studies hitherto made that both Cu-based NMs and released Cu2+ may be the main reasons for toxicity. When Cu-based NMs enter the soil-plant environment, their intrinsic physicochemical properties, along with various environmental factors, could also affect their transport, transformation, and biotoxicity. Therefore, we should push for intensifying the multi-approach research that focuses on the behaviors of Cu-based NMs in terrestrial exposure environments, and mitigates their toxicity to ensure the promotion of Cu-based NMs.

LiaSR two-component system modulates the oxidative stress response in Streptococcusmutans

Many commensal bacteria of the human oral microbiome can produce reactive oxygen species (ROS). ROS will inhibit the colonization of Streptococcusmutans (S.mutans), a major pathogenic bacteria in dental caries. The LiaSR two-component system in S.mutans can sense and respond to environmental oxidative stress. However, the molecular details of the LiaSR two-component system and oxidative stress response have been unclear. In this study, we aimed to elucidate the underlying mechanisms of the LiaSR two-component system and the mediated oxidative stress response in S.mutans. We performed the H2O2 killing assay, Confocal laser scanning microscopy, and 2,7-Dichlorofluoresce diacetate staining assay to evaluate the sensitivity of S.mutans to H2O2. The propidium iodide probe and TUNEL kit were used to detect the membrane permeability and DNA fragmentation. Quantitative real-time PCR was conducted to analyze the expression level of underlying regulated genes. The liaS and liaR deficient mutants were particularly sensitive to H2O2 compared to their wild strain S.mutans 593, which was previously isolated from a caries-active patient. The intracellular levels of ROS and membrane permeability increased in the mutants. The TUNEL assay showed that the rate of DNA fragmentation in the liaR mutant was higher compared to the wild strain and liaS mutant. Relative expression of the spxA2 gene in the mutants was lower than in the wild strain. The dpr and dinB genes were downregulated in the liaR mutant. These results indicated that the LiaSR two-component system mediated influence on spxA2 expression in S.mutans and contributed to membrane homeostasis, which was involved in the oxidative response process. S.mutans could also elevate the dpr and the dinB genes, which depend on the liaR component in the LiaSR system, may help reduce the DNA damage caused by ROS. This study provides valuable insights into the mechanisms of the LiaSR two-component system in the oxidative stress response of S.mutans.

Effects of l-Serine on Macrolide Resistance in Streptococcus suis

Streptococcus suis is an important zoonotic pathogen. Due to the indiscriminate use of macrolides, S. suis has developed a high level of drug resistance, which has led to a serious threat to human and animal health. However, it takes a long time to develop new antibacterial drugs. Therefore, we consider the perspective of bacterial physiological metabolism to ensure that the development of bacterial resistance to existing drugs is alleviated and bacterial susceptibility to drugs is restored. In the present study, an untargeted metabolomics analysis showed that the serine catabolic pathway was inhibited in drug-resistant S. suis. The addition of l-serine restored the fungicidal effect of macrolides on S. suisin vivo and in vitro by enhancing the serine metabolic pathway. Further studies showed that l-serine, stimulated by its serine catabolic pathway, inhibited intracellular H₂S production, reduced Fe-S cluster production, and restored the normal occurrence of the Fenton reaction in cells. It also attenuated the production of glutathione, an important marker of the intracellular oxidation-reduction reaction. All these phenomena eventually contribute to an increase in the level of reactive oxygen species, which leads to intracellular DNA damage and bacterial death. Our study provides a potential new approach for the treatment of diseases caused by drug-resistant S. suis.

IMPORTANCE The emergence of antimicrobial resistance is a global challenge. However, new drug development efforts consume considerable resources and time, and alleviating the pressure on existing drugs is the focus of our work. We investigated the mechanism of action of l-serine supplementation in restoring the use of macrolides in S. suis, based on the role of the serine catabolic pathway on reactive oxygen species levels and oxidative stress in S. suis. This pathway provides a theoretical basis for the rational use of macrolides in clinical practice and also identifies a possible target for restoring drug sensitivity in S. suis.