Autoregulation of the Escherichia coli melR promoter: repression involves four molecules of MelR

The Escherichia coli MelR protein is a transcription activator that autoregulates its own promoter by repressing transcription initiation. Optimal repression requires MelR binding to a site that overlaps the melR transcription start point and to upstream sites. In this work, we have investigated the different determinants needed for optimal repression and their spatial requirements. We show that repression requires a complex involving four DNA-bound MelR molecules, and that the global CRP regulator plays little or no role

Rapid Microbiological Testing: Monitoring the Development of Bacterial Stress

The ability to respond to adverse environments effectively along with the ability to reproduce are sine qua non conditions for all sustainable cellular forms of life. Given the availability of an appropriate sensing modality, the ubiquity and immediacy of the stress response could form the basis for a new approach for rapid biological testing. We have found that measuring the dielectric permittivity of a cellular suspension, an easily measurable electronic property, is an effective way to monitor the response of bacterial cells to adverse conditions continuously. The dielectric permittivity of susceptible and resistant strains of Escherichia coli and Staphylococcus aureus, treated with gentamicin and vancomycin, were measured directly using differential impedance sensing methods and expressed as the Normalized Impedance Response (NIR). These same strains were also heat-shocked and chemically stressed with Triton X-100 or H2O2. The NIR profiles obtained for antibiotic-treated susceptible organisms showed a strong and continuous decrease in value. In addition, the intensity of the NIR value decrease for susceptible cells varied in proportion to the amount of antibiotic added. Qualitatively similar profiles were found for the chemically treated and heat-shocked bacteria. In contrast, antibiotic-resistant cells showed no change in the NIR values in the presence of the drug to which it is resistant. The data presented here show that changes in the dielectric permittivity of a cell suspension are directly correlated with the development of a stress response as well as bacterial recovery from stressful conditions. The availability of a practical sensing modality capable of monitoring changes in the dielectric properties of stressed cells could have wide applications in areas ranging from the detection of bacterial infections in clinical specimens to antibiotic susceptibility testing and drug discovery

Wood Utilization Is Dependent on Catalase Activities in the Filamentous Fungus Podospora anserina

Catalases are enzymes that play critical roles in protecting cells against the toxic effects of hydrogen peroxide. They are implicated in various physiological and pathological conditions but some of their functions remain unclear. In order to decipher the role(s) of catalases during the life cycle of Podospora anserina, we analyzed the role of the four monofunctional catalases and one bifunctional catalase-peroxidase genes present in its genome. The five genes were deleted and the phenotypes of each single and all multiple mutants were investigated. Intriguingly, although the genes are differently expressed during the life cycle, catalase activity is dispensable during both vegetative growth and sexual reproduction in laboratory conditions. Catalases are also not essential for cellulose or fatty acid assimilation. In contrast, they are strictly required for efficient utilization of more complex biomass like wood shavings by allowing growth in the presence of lignin. The secreted CATB and cytosolic CAT2 are the major catalases implicated in peroxide resistance, while CAT2 is the major player during complex biomass assimilation. Our results suggest that P. anserina produces external H2O2 to assimilate complex biomass and that catalases are necessary to protect the cells during this process. In addition, the phenotypes of strains lacking only one catalase gene suggest that a decrease of catalase activity improves the capacity of the fungus to degrade complex biomass

Cross-Talk between the Cellular Redox State and the Circadian System in Neurospora

The circadian system is composed of a number of feedback loops, and multiple feedback loops in the form of oscillators help to maintain stable rhythms. The filamentous fungus Neurospora crassa exhibits a circadian rhythm during asexual spore formation (conidiation banding) and has a major feedback loop that includes the FREQUENCY (FRQ)/WHITE COLLAR (WC) -1 and -2 oscillator (FWO). A mutation in superoxide dismutase (sod)-1, an antioxidant gene, causes a robust and stable circadian rhythm compared with that of wild-type (Wt). However, the mechanisms underlying the functions of reactive oxygen species (ROS) remain unknown. Here, we show that cellular ROS concentrations change in a circadian manner (ROS oscillation), and the amplitudes of ROS oscillation increase with each cycle and then become steady (ROS homeostasis). The ROS oscillation and homeostasis are produced by the ROS-destroying catalases (CATs) and ROS-generating NADPH oxidase (NOX). cat-1 is also induced by illumination, and it reduces ROS levels. Although ROS oscillation persists in the absence of frq, wc-1 or wc-2, its homeostasis is altered. Furthermore, genetic and biochemical evidence reveals that ROS concentration regulates the transcriptional function of WCC and a higher ROS concentration enhances conidiation banding. These findings suggest that the circadian system engages in cross-talk with the cellular redox state via ROS-regulatory factors

Intraoperative oxygen tension and redox homeostasis in Pseudomyxoma peritonei: A short case series

IntroductionPseudomyxoma peritonei (PMP) is a rare malignant disease characterized by a massive multifocal accumulation of mucin within the peritoneal cavity. The current treatment option is based on complete cytoreductive surgery combined with hyperthermic intraperitoneal chemotherapy. However, the recurrence is frequent with subsequent progression and death. To date, most of the studies published in PMP are related to histological and genomic analyses. Thus, the need for further studies unveiling the underlying PMP molecular mechanisms is urgent. In this regard, hypoxia and oxidative stress have been extensively related to tumoral pathologies, although their contribution to PMP has not been elucidated.MethodsIn this manuscript, we have evaluated, for the first time, the intratumoral real-time oxygen microtension (pO2mt) in the tumor (soft and hard mucin) and surrounding healthy tissue from five PMP patients during surgery. In addition, we measured hypoxia (Hypoxia Inducible Factor-1a; HIF-1α) and oxidative stress (catalase; CAT) markers in soft and hard mucin from the same five PMP patient samples and in five control samples.ResultsThe results showed low intratumoral oxygen levels, which were associated with increased HIF-1α protein levels, suggesting the presence of a hypoxic environment in these tumors. We also found a significant reduction in CAT activity levels in soft and hard mucin compared with healthy tissue samples.DiscussionIn conclusion, our study provides the first evidence of low intratumoral oxygen levels in PMP patients associated with hypoxia and oxidative stress markers. However, further investigation is required to understand the potential role of oxidative stress in PMP in order to find new therapeutic strategies

Gut microbiota: In sickness and in health

Peer Reviewe

The XylS/AraC family of regulators.

At least twenty-seven proteins belong to the XylS/AraC family of prokaryote transcriptional regulators. All members of this family except CelD and TetD are positive transcriptional factors. Three subgroups were distinguished within the family in accordance with the Needleman and Wunsch algorithm. Multiple alignment of these proteins revealed that they shared a high degree of sequence homology at their C-terminal end, where a characteristic conserved motif, whose consensus sequence is I-DIA--GF-S--YF--F---G-TPS--R (where - means any aminoacid), was found. Within the homologous C-terminal region, but outside the above consensus motif, a putative DNA-binding domain organized as a helix-turn-helix motif was located in all regulators. For regulators recognizing chemical signals, the non-homologous N-terminal region of these regulators is presumed to contain binding sites for activator molecules that confer specificity