Anthrax toxin component, Protective Antigen, protects insects from bacterial infections

Abstract

Anthrax is a major zoonotic disease of wildlife, and in places like West Africa, it can be caused by Bacillus anthracis in arid nonsylvatic savannahs, and by B. cereus biovar anthracis (Bcbva) in sylvatic rainforests. Bcbva-caused anthrax has been implicated in as much as 38% of mortality in rainforest ecosystems, where insects can enhance the transmission of anthrax-causing bacteria. While anthrax is well-characterized in mammals, its transmission by insects points to an unidentified anthrax-resistance mechanism in its vectors. In mammals, a secreted anthrax toxin component, 83 kDa Protective Antigen (PA 83), binds to cellsurface receptors and is cleaved by furin into an evolutionary-conserved PA 20 and a poreforming PA 63 subunits. We show that PA 20 increases the resistance of Drosophila flies and Culex mosquitoes to bacterial challenges, without directly affecting the bacterial growth. We further show that the PA 83 loop known to be cleaved by furin to release PA 20 from PA 63 is, in part, responsible for the PA 20-mediated protection. We found that PA 20 binds directly to the Toll activating peptidoglycan-recognition protein-SA (PGRP-SA) and that the Toll/NF-κB pathway is necessary for the PA 20-mediated protection of infected flies. This effect of PA 20 on innate immunity may also exist in mammals: we show that PA 20 binds to human PGRP-SA ortholog. Moreover, the constitutive activity of Imd/NF-κB pathway in MAPKK Dsor1 mutant flies is sufficient to confer the protection from bacterial infections in a manner that is independent of PA 20 treatment. Lastly, Clostridium septicum alpha toxin protects flies from anthrax-causing bacteria, showing that other pathogens may help insects resist anthrax. The mechanism of anthrax resistance in insects has direct implications on insect-mediated anthrax transmission for wildlife management, and with potential for applications, such as reducing the sensitivity of pollinating insects to bacterial pathogens.

In Vivo Activity of Repurposed Amodiaquine as a Host-Targeting Therapy for the Treatment of Anthrax

“…Drosophila 66 Extra-thick Whatman blotting paper (Bio-Rad Laboratories, 1703965) was cut into 25 mm diameter discs, and three stacked discs were placed into the bottom of 25 mm diameter polystyrene Drosophila vials, following by capping with a foam plug. All overnight bacterial cultures were centrifuged, and the bacterial pellets were resuspended in a 50 mM sucrose solution to a final OD 600 of 3.3.…”

“…Flies were maintained at 25 °C with 12-h light/dark cycles and fed standard cornmeal-molasses-agar fly medium with yeast flakes. Flies were infected according to the bacterial intestinal infection method . Extra-thick Whatman blotting paper (Bio-Rad Laboratories, 1703965) was cut into 25 mm diameter discs, and three stacked discs were placed into the bottom of 25 mm diameter polystyrene Drosophila vials, following by capping with a foam plug.…”

Anthrax disease burden: Impact on animal and human health

“…Anthrax spores in the air enter the respiratory tract through the inhalation route, digestive tract through the gastrointestinal route, and through the skin [4]. Human anthrax can potentially be spread through bug bites [58]. Inhaled anthrax spores immediately germinate and release significant toxins [59].…”

ANTHRAX: LIFE CYCLE, MECHANISMS OF PATHOGENESIS AND PROSPECTS IN THE DEVELOPMENT OF VETERINARY VACCINES (review)

“…Недавно описана новая функция РА20 и предложен РА20-опосредованный механизм, с помощью которого насекомые -переносчики B. anthracis, приобретают устойчивость к сибирской язве за счет активации врожденного иммунитета. По мнению авторов, подобный механизм может существовать и у млекопитающих (47).…”