How Bacterial Redox Sensors Transmit Redox Signals via Structural Changes

Oxygen-induced evolution of anammox granular sludge explains its unique responses during preservation

Anammox granular sludge (AnGS) preservation is indispensable for the application of anammox technology. Oxygen is a common and crucial factor for anammox, yet its long-term effects on AnGS during preservation remain incomplete clarification. This study investigated the effect of oxygen on AnGS in two simulated preservation systems with open and sealed conditions, and the mechanism was discussed. The results showed that the open system was in an oxidized state with an average dissolved oxygen (DO) concentration and oxidation-reduction potential (ORP) of (3.10 ± 1.36) mg·L-1 and (112.58 ± 46.78) mV, while a reduced state for the sealed system with no detected DO and a lower average ORP of (-153.96 ± 64.32) mV. Both systems showed declines in AnGS activity, while with different responses of AnGS demonstrated by the evolution in terms of granular morphology and structure, bacterial communities, bacteria survival, and bacteria antioxidation. In the open system, reactive oxygen species were generated and destroyed the unsaturated fatty acids in the cell membrane, further leading to the destructed cell structure and declined activity. However, in the sealed system, AnAOB tended to enter a dormant state after long-term preservation, contributing to better conditions in granular morphology and structure, higher AnAOB abundance, and higher live cell ratio. The findings of this study are expected to offer vital information and guidelines for the preservation technologies of AnGS.

Redox active plant phenolic, acetosyringone, for electrogenetic signaling

Redox is a unique, programmable modality capable of bridging communication between biology and electronics. Previous studies have shown that the E. coli redox-responsive OxyRS regulon can be re-wired to accept electrochemically generated hydrogen peroxide (H2O2) as an inducer of gene expression. Here we report that the redox-active phenolic plant signaling molecule acetosyringone (AS) can also induce gene expression from the OxyRS regulon. AS must be oxidized, however, as the reduced state present under normal conditions cannot induce gene expression. Thus, AS serves as a "pro-signaling molecule" that can be activated by its oxidation-in our case by application of oxidizing potential to an electrode. We show that the OxyRS regulon is not induced electrochemically if the imposed electrode potential is in the mid-physiological range. Electronically sliding the applied potential to either oxidative or reductive extremes induces this regulon but through different mechanisms: reduction of O2 to form H2O2 or oxidation of AS. Fundamentally, this work reinforces the emerging concept that redox signaling depends more on molecular activities than molecular structure. From an applications perspective, the creation of an electronically programmed "pro-signal" dramatically expands the toolbox for electronic control of biological responses in microbes, including in complex environments, cell-based materials, and biomanufacturing.

Metalloprotein enabled redox signal transduction in microbes

Microbes utilize numerous metal cofactor-containing proteins to recognize and respond to constantly fluctuating redox stresses in their environment. Gaining an understanding of how these metalloproteins sense redox events, and how they communicate such information downstream to DNA to modulate microbial metabolism, is a topic of great interest to both chemists and biologists. In this article, we review recently characterized examples of metalloprotein sensors, focusing on the coordination and oxidation state of the metals involved, how these metals are able to recognize redox stimuli, and how the signal is transmitted beyond the metal center. We discuss specific examples of iron, nickel, and manganese-based microbial sensors, and identify gaps in knowledge in the field of metalloprotein-based signal transduction pathways.

Optimization of a Method for Detecting Intracellular Sulfane Sulfur Levels and Evaluation of Reagents That Affect the Levels in Escherichia coli

Sulfane sulfur is a class of compounds containing zero-valent sulfur. Most sulfane sulfur compounds are reactive and play important signaling roles. Key enzymes involved in the production and metabolism of sulfane sulfur have been characterized; however, little is known about how to change intracellular sulfane sulfur (iSS) levels. To accurately measure iSS, we optimized a previously reported method, in which reactive iSS reacts with sulfite to produce thiosulfate, a stable sulfane sulfur compound, before detection. With the improved method, several factors were tested to influence iSS in Escherichia coli. Temperature, pH, and osmotic pressure showed little effect. At commonly used concentrations, most tested oxidants, including hydrogen peroxide, tert-butyl hydroperoxide, hypochlorous acid, and diamide, did not affect iSS, but carbonyl cyanide m-chlorophenyl hydrazone increased iSS. For reductants, 10 mM dithiothreitol significantly decreased iSS, but tris(2-carboxyethyl)phosphine did not. Among different sulfur-bearing compounds, NaHS, cysteine, S₂O₃²⁻ and diallyl disulfide increased iSS, of which only S₂O₃²⁻ did not inhibit E. coli growth at 10 mM or less. Thus, with the improved method, we have identified reagents that may be used to change iSS in E. coli and other organisms, providing tools to further study the physiological functions of iSS.

The oxidative stress and metabolic response of Acinetobacter baumannii for aPDT multiple photosensitization

The use of antimicrobial photodynamic inactivation as a non-antibiotic alternative method to inactivate Acinetobacter baumannii was described in response to the ever-growing problem of antibiotic resistance. It was found that irradiation of the bacterial suspension for 10 min reduced the number of viable cells by approximately 99% and this energy fluence was considered to be sub-lethal phototherapy. The lethal dose of laser light (cell mortality about 99.9%) was 9.54 J cm⁻², which corresponds to 30 min of irradiation. After a 15-fold phototherapy cycle, the tolerance to aPDT decreased, resulting in a decrease in the number of viable cells by 2.15 and 3.23 log₁₀ CFU/ml units with the use of sub-lethal and lethal light doses, respectively. Multiple photosensitizations decreased the biofilm formation efficiency by 25 ± 1% and 35 ± 1%, respectively. No changes in antibiotic resistance were observed, whereas the cells were more sensitive to hydrogen peroxide. Metabolomic changes after multiple photosensitization were studied and ¹H NMR measurements were used in statistical and multivariate data analysis. Many significant changes in the levels of the metabolites were detected demonstrating the response of A. baumannii to oxidative stress.

Influence of Redox Imbalances on the Transposition of Insertion Sequences in Deinococcus geothermalis

The transposition of insertion sequence elements was evaluated among different Deinococcus geothermalis lineages, including the wild-type, a cystine importer-disrupted mutant, a complemented strain, and a cystine importer-overexpressed strain. Cellular growth reached early exponential growth at OD₆₀₀ 2.0 and late exponential growth at OD₆₀₀ 4.0. Exposing the cells to hydrogen peroxide (80–100 mM) resulted in the transposition of insertion sequences (ISs) in genes associated with the carotenoid biosynthesis pathway. Particularly, ISDge7 (an IS5 family member) and ISDge5 (an IS701 family member) from the cystine importer-disrupted mutant were transposed into phytoene desaturase (dgeo_0524) via replicative transposition. Further, the cystine importer-overexpressed strain Δdgeo_1985R showed transposition of both ISDge2 and ISDge5 elements. In contrast, IS transposition was not detected in the complementary strain. Interestingly, a cystine importer-overexpressing strain exhibited streptomycin resistance, indicating that point mutation occurred in the rpsL (dgeo_1873) gene encoding ribosomal protein S12. qRT-PCR analyses were then conducted to evaluate the expression of oxidative stress response genes, IS elements, and low-molecular-weight thiol compounds such as mycothiol and bacillithiol. Nevertheless, the mechanisms that trigger IS transposition in redox imbalance conditions remain unclear. Here, we report that the active transposition of different IS elements was affected by intracellular redox imbalances caused by cystine importer deficiencies or overexpression.