Exploring the impact of fungicide exposure and nutritional stress on the microbiota and immune response of the Cape honey bee (Apis mellifera capensis).

Honey bees (Apis mellifera) harbour a stable core microbial community within their gut, that is suggested to play a role in metabolic functioning, immune regulation, and host homeostasis. This microbiota presents a unique opportunity to observe the effects of stressors on honey bee health. We examined the effects of two common honey bee stressors: indirect fungicide contamination and nutrient limitation. These effects were observed through changes in their hind- and midgut microbiota using Automated Ribosomal Intergenic Spacer Analysis (ARISA), alongside high-throughput amplicon sequencing. Expression of the honey bees' immune response was examined through the expression of three immune-related genes, namely, immune deficiency (imd), proPhenolOxidase (proPO), and spaetzle (spz). Additionally, longevity of the honey bees was monitored through observation of the expression levels of Vitellogenin (Vg). Both treatment groups were compared to a negative control, and a diseased positive control. There was no effect on the hindgut microbiota due to the stressors, while significant changes in the midgut was observed. This was also observed in the expression of the immune-related genes within the treatment groups. The Imd pathway was substantially downregulated, with upregulation in the prophenoloxidase pathway. However, no significant effect was observed in the expression of spz, and only the pollen treatment group showed reduced longevity through a downregulation of Vg. Overall, the effect of these two common stressors indicate a compromise in honey bee immunity, and potential vulnerabilities within the immune defence mechanisms.

Application of Paracoccus marcusii as a potential feed additive for laying hens.

Carotenoids have been used for many years as an added pigment to enhance egg yolk color. One such carotenoid, astaxanthin, has a strong antioxidant activity and is produced by several microorganisms, including the bacterium Paracoccus marcusii, which has shown promise to be used as a feed additive. Therefore, this study investigated the use of P. marcusii as a possible source of pigmentation in layer hen feed to enhance egg yolk color. Paracoccus marcusii was fed to hens in a sucrose solution (10% m/v). The hens were fed daily and all eggs were collected for analysis. Dilutions of egg contents were plated onto selective media to detect the presence of known food pathogens (E. coli, Listeria, and Salmonella). In the feeding trial, there was no negative effect on hen body weight, egg production, or overall egg quality. There was a significant increase (P < 0.05) in yolk color as well as an increase in whole egg and yolk weight. There were also no known food pathogens detected in any of the egg samples. This study has shown promising results in using this bacterium as an effective feed additive for laying hens.