Increased toxicity of low oxygen atmospheres supplemented with carbon dioxide on Tribolium castaneum adults

T. castaneum adults were exposed to atmospheres containing O₂ concentrations of 2%–5% supplemented with 5%–35% CO₂ at 26° and 30° for 24–120 hr at 57% relative humidity. Mortality of insects at the given O₂ concentrations was higher when the level of the added CO₂ was increased, the temperature was higher and the exposure time was extended. A significant interaction was found between the levels of O₂ and CO₂ tested, indicating the clear synergistic effect of these two gases on the mortality of test insects.

---

résumé Des groupes d'adultes de 7 à 10 jours de T. castaneum ont été exposés à des atmosphères à teneurs en O₂ de 2, 3, 4 et 5% avec enrichissement en CO₂ variant entre 5% et 35%. Les expériences, effectuées aux températures 26° et 30° et 57% d'humidité relative, ont duré 120 heures.Aucune mortalité totale n'a été observée chez les insectes exposés aux faibles concentrations d'O₂ sans addition de CO₂, tandis qu'à 2% de O₂ une addition de 10% de CO₂ provoque à 26° une mortalité totale; le même résultat est obtenu à 30° en ajoutant seulement du CO₂ à 5%. Quand la teneur en O₂ est de 5%, il faut 35% de CO₂ pour obtenir une mortalité totale aux deux températures.Pour une concentration en O₂ donnée, la mortalité augmente avec la concentration en CO₂, la température et la durée d'exposition. Il y a des actions réciproques réelles entre les concentrations en O₂ et CO₂, ce qui montre un effet typiquement synergique des deux gaz sur la mortalité des T. castaneum testés.

     

More than just a pair of blue genes: how cyanobacteria adapt to changes in their light environment

Cyanobacteria require light to perform photosynthesis, but not all colors of light are equally useable for them. In particular, blue light-grown cyanobacterial strains, including the well-studied model organism Synechocystis sp. PCC 6803 (Synechocystis), have been observed to exhibit slower growth rates than white or red light-grown cells. In this issue of Physiologia Plantarum, Luimstra et al. (2020) have attempted to understand why cyanobacterial cells suffer under blue light. They measured the molecular and genetic responses of Synechocystis cells to being shifted from white light to blue light. They found that blue light-grown cells make changes that lead to a redistribution of energy flow between the two photosystems that power photosynthesis. These findings could help researchers identify avenues for optimizing photosynthesis in cyanobacterial species, a group of organisms which show great promise as potential solar-powered factories for the production of biofuels and other high-value products.     

TAC from Mycobacterium tuberculosis: a paradigm for stress-responsive toxin–antitoxin systems controlled by SecB-like chaperones

Bacterial type II toxin–antitoxins (TAs) are two-component systems that modulate growth in response to specific stress conditions, thus promoting adaptation and persistence. The major human pathogen Mycobacterium tuberculosis potentially encodes 75 TAs and it has been proposed that persistence induced by active toxins might be relevant for its pathogenesis. In this work, we focus on the newly discovered toxin–antitoxin–chaperone (TAC) system of M. tuberculosis, an atypical stress-responsive TA system tightly controlled by a molecular chaperone that shows similarity to the canonical SecB chaperone involved in Sec-dependent protein export in Gram-negative bacteria. We performed a large-scale genome screening to reconstruct the evolutionary history of TAC systems and found that TAC is not restricted to mycobacteria and seems to have disseminated in diverse taxonomic groups by horizontal gene transfer. Our results suggest that TAC chaperones are evolutionary related to the solitary chaperone SecB and have diverged to become specialized toward their cognate antitoxins.     

Circulating antigens and antibodies in human and mouse dermatophytosis: use of monoclonal antibody reactive to phosphorylcholine-like epitopes

The presence of circulating antibodies in the sera of patients infected with either Trichophyton concentricum or Trichophyton rubrum, and in the sera of BALB/c mice chronically infected with Trichophyton quinckeanum, was determined by ELISA. High levels of antibody to dermatophyte cytoplasmic antigens were detected both in infected humans and in mice. Partial inhibition of this reaction was observed by pretreatment of the sera with the hapten phosphorylcholine (PC). Moreover, antibodies were shown to have some reactivity with PC when tested by ELISA against PC conjugated to bovine serum albumin. Significant levels of circulating antigen were detected in patients with T. concentricum and T. rubrum infections, but not in uninfected subjects, by an immunoradiometric assay using a monoclonal antibody, Tq-1, which reacts with the PC-like epitopes of dermatophytes. It is possible that this dermatophyte antigen may play a role in modulating the cell-mediated immune responses, which would appear to be defective in most patients with these chronic forms of dermatophytosis.