Immune and antioxidant gene expression stimulation of Apis mellifera (Hymenoptera: Apidae) larvae by Saccharomyces cerevisiae from the brewering industry

The high overwinter mortalities in the honey bee population of Apis mellifera have been linked to immunocompromised individuals experiencing nutritional limitations. Larval nutrition plays a crucial role in determining the successful development of adults, making them more susceptible to bacterial diseases when undernourished. One of the main intracellular signalling pathways in the larval immune system against bacterial diseases is the Toll receptor signalling pathway, which activates antimicrobial peptides like defensin. Inadequate nutrition also disrupts the redox balance on A. mellifera individuals, with superoxide dismutase and catalase being the key components of their antioxidant system. Vitellogenin is associated with the mobilization of nutrients in early A. mellifera bee stages. Considering that Saccharomyces cerevisiae is the second most significant by-product of the brewing industry, it may serve as a valuable raw material. We investigated the impact of feeding larvae with live S. cerevisiae cells on the relative expression of their main immune and antioxidant-related genes. To assess gene expression, we conducted RT-qPCR, using RNA extracted from ten larvae per treatment on the seventh day when the feeding trial concluded. Importantly, the presence of S. cerevisiae did not affect larval survival compared to the control group. However, the relative expression of immune-related gene toll18W and antioxidant-related gene sod in larvae fed with live S. cerevisiae cells was significantly higher than in larvae that were not fed with them. This suggests that the inclusion of S. cerevisiae in their diet may provide larvae with a nutritional advantage. Additionally, the vitellogenin (vg) gene expression increased in treated larvae compared to the control group, potentially facilitating their access to nutrients and, consequently, enhancing their ability to cope with nutritional stress.