Ascosphaera apis as a target for the antifungal activity of symbiotic Bifidobacteria in honey bees

Massimo Iorizzo¹Sonia Ganassi^1*Bruno Testa¹Licia Maria Di Donato¹Gianluca Albanese^1*Mariantonietta Succi¹Francesca Coppola²Rosaria Cozzolino³Cristina Matarazzo¹Dalila Di Criscio¹Cosimo Tedino¹Antonio De Cristofaro¹

• ¹Department of Agriculture, Environmental and Food Science, University of Molise, Campobasso, Italy
• ²Universita degli Studi di Napoli Federico II, Naples, Italy
• ³Istituto di Scienze dell'Alimentazione Consiglio Nazionale delle Ricerche, Avellino, Italy

The genus Bifidobacterium is a key component of the honey bee gut microbiota, playing a fundamental role in maintaining host health and colony well-being. Alongside other core genera such as Bombilactobacillus, Gilliamella, Lactobacillus, and Snodgrassella, Bifidobacterium contributes to essential functions including nutrient digestion, immune modulation, and protection against pathogens. Among threats to honey bee health, Chalkbrood disease, caused by fungus Ascosphaera apis, remains a major concern due to detrimental effects on colony strength and honey yield. We characterized enzymatic activity and carbohydrate assimilation of nine Bifidobacterium strains isolated from honey bee intestinal tract. In parallel, we assessed antifungal potential against A. apis strains, focusing on volatile organic compounds (VOCs). Notably, Bifidobacterium asteroides 3CP-2B exhibited enzymatic capabilities supporting digestive functions and metabolism of sugars potentially harmful to honey bees. This strain showed marked antifungal activity against A. apis, mediated by volatile and nonvolatile bioactive metabolites. Among VOCs identified, propanoic acid, ethanol, acetic acid, ethyl propionate, and 1-propanol were the most prominent compounds associated with the antifungal effect.