Drosophila melanogaster Selection for Survival after Infection with Bacillus cereus Spores: Evolutionary Genetic and Phenotypic Investigations of Respiration and Movement

A protein restricted diet induces a stable increased fat storage phenotype in flies

Background

Scientific evidence has revealed possible confounders in diet induced obesity models of Drosophila melanogaster. High Sugar Diet (HSD) induction of obesity in flies has been associated with fly hyperosmolarity and glucotoxicity, while High Fat Diet (HFD) induction has been associated with lipotoxicity. The objective of this study was to assess for a healthy obesity phenotype by comparison of fly survival, physio-chemical and biochemical changes associated with HSD, HFD and Protein Restricted Diet (PRD) obesity induction models of male Drosophila melanogaster. Here, we provide information on a PRD as the plausible option in obesity research not involving cancer, diabetes, glucotoxicity and lipotoxicity studies.

Methods

Obesity was induced by exposing Drosophila melanogaster white mutant w¹¹¹⁸ to four experimental diets for four weeks. Group 1 was fed regular food (control), group 2 was fed a 0.5% less yeast than in regular feed (PRD), group 3 was fed a 30% w/v sucrose to regular cornmeal food (HSD) and group 4 was fed a 10% w/v food-grade coconut oil to regular cornmeal food (HFD). Peristaltic waves were measured on 3rd instar larvae of all experimental groups. Negative geotaxis, fly survival, body mass, catalase activity, triglycerides (TG/TP), sterol, and total protein were measured in adult Drosophila melanogaster after four weeks.

Results

Triglycerides (TG/TP) and total protein levels were significantly higher in HSD phenotype. Sterols were higher in HFD phenotype. Though catalase enzyme activity was highest in PRD phenotype, this activity was not statistically significant when compared to that of HSD and HFD phenotypes. However, PRD phenotype had the lowest mass, highest survival rate and the highest negative geotaxis, thus demonstrating a balanced, stable and more viable metabolic status in the experimental model.

Conclusion

A protein restricted diet induces a stable increased fat storage phenotype in Drosophila melanogaster.

Anti-obesity effects of Erythrina abyssinica stem bark extract in flies exposed to a high fat diet

Background

An in vitro assay on Sigmoidin A from Erythrina abyssinica stem bark revealed its potency to inhibit pancreatic lipase. However, studies indicate activity of extract bioactive compounds in combination far exceed the favorable effects of each individual compound due to synergy and additive effects. In this study, we provide information on the effect of E. abyssinica stem bark extract in Drosophila melanogaster. The objective of the study was to determine the safety and effects of E. abyssinica stem bark extract on fly survival, body weight, triglycerides, sterol, total protein, and catalase activity of obese male D. melanogaster.

Methods

Obesity was induced by exposing D. melanogaster white mutant w¹¹¹⁸ to coconut food for two weeks. Groups 1–3 were fed on coconut food + fenofibrate at 25 mM, 50 mM, and 75 mM. Groups 4–6 were fed on coconut food + E. abyssinica stem bark extract at concentrations of 2.5 g/ml, 5.0 g/ml, and 7.5 g/ml. The positive control was exposed to only coconut food while the negative control was on regular food. Fly survival observations were done for 15 days, while acute and chronic effects were done at 30 min and after 48 h respectively following treatment. Body mass, negative geotaxis, reducing power of the extract, triglycerides (TG/TP), sterol, total protein levels, and catalase activity were measured after 10 days of exposure to the experimental diets.

Results

Fly survival changes were observed after 10 days and E. abyssinica stem bark extract had the strongest reducing power at 7.5 g/ml extract concentration. E. abyssinica stem bark extract reduced body mass, triglyceride levels (TG/TP), sterol levels, and modulated catalase activity at 7.5 g/ml extract concentration. Though the standard drug fenofibrate had the highest fat accumulation reduction potential, the extract at 7.5 g/ml was much safer in reducing fat accumulation in obese male D. melanogaster than other concentration used.

Conclusion

Antioxidants in E. abyssinica stem bark extract are responsible for the observed anti-obesity activity.

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

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 (PA83), binds to cell-surface receptors and is cleaved by furin into an evolutionary-conserved PA20 and a pore-forming PA63 subunits. We show that PA20 increases the resistance of Drosophila flies and Culex mosquitoes to bacterial challenges, without directly affecting the bacterial growth. We further show that the PA83 loop known to be cleaved by furin to release PA20 from PA63 is, in part, responsible for the PA20-mediated protection. We found that PA20 binds directly to the Toll activating peptidoglycan-recognition protein-SA (PGRP-SA) and that the Toll/NF-κB pathway is necessary for the PA20-mediated protection of infected flies. This effect of PA20 on innate immunity may also exist in mammals: we show that PA20 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 PA20 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.