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Title: Glucose oxidase production does not increase after colony infection: Testing its role in honey bee social immunity

Author
item LOPEZ-URIBE, MARGARITA - Pennsylvania State University
item Simone-Finstrom, Michael

Submitted to: Bee World
Publication Type: Proceedings
Publication Acceptance Date: 2/7/2017
Publication Date: 3/2/2017
Citation: Lopez-Uribe, M.M., Simone-Finstrom, M. 2017. Glucose oxidase production does not increase after colony infection: Testing its role in honey bee social immunity. Bee World. 93(4):104-127.

Interpretive Summary: Honey bees rely on a variety of defense mechanisms to reduce disease infection and spread throughout the colony. Hygienic behavior, resin collection, and production of antimicrobial compounds are some examples of defenses that bees use against parasites. Many of these defenses rely on the collective action of multiple individuals to prevent, reduce or eradicate pathogens—often referred as social immunity. Glucose oxidase (GOX) is an enzyme that produces hydrogen peroxide, a compound with antiseptic properties. GOX and some antimicrobial peptides (e.g. Defensin-1) are secreted by the hypopharyngeal gland of bees to help sterilize food (e.g., honey) and are included as part of the glandular secretions fed to developing larvae. Whether or not nurse bees increase in the amount of GOX they produce, and presumably feed to larvae, when the colony is infected by pathogens is currently unclear. This research aimed to address that question see to what level GOX is used as a type of social immunity or colony-level defense against pathogens.

Technical Abstract: Honey bees rely on a variety of defense mechanisms to reduce disease infection and spread throughout the colony. Hygienic behavior, resin collection, and antimicrobial peptide production are some examples of defenses that bees use against parasites (Evans & Spivak, 2010 J Invertebr Pathol 103:S62). Many of these defenses rely on the collective action of multiple individuals to prevent, reduce or eradicate pathogens—often referred as 'social immunity' (Cremer et al., 2007 Curr Biol 17:R693). Glucose oxidase (GOX) is an enzyme that produces hydrogen peroxide, a compound with antiseptic properties. GOX and some antimicrobial peptides (e.g. Defensin-1) are secreted by the hypopharyngeal gland of bees to help sterilize food (e.g., honey) and are present as part of the glandular secretions fed to developing larvae. Because of their antiseptic properties and presence in larval food and colony food stores, GOX, in particular, has been used as a “biomarker” for social immunity (Alaux et al., 2010 Environ Microbiol 12:774). However, the direct role that GOX has as a colony-level immune mechanism has not previously been studied. The aim of this study was to investigate if GOX production increases at the colony level after pathogen exposure to determine if they are compounds that can be induced in worker bees to protect larvae from infection. Specifically, we tested whether GOX activity changes after a colony-level bacterial infection by American Foulbrood (AFB, Paenibacillus larvae). We quantified GOX activity in 7 day old and 14 day old honey bee adults before and after bacterial infection using enzymatic assays and transcript expression quantification. We did not detect a change in GOX enzymatic activity between control and AFB infected bees 7 day old (F= 0.01, P= 0.923) or 14 day old (F= 0.116, P= 0.752) bees (see Figure). These results were corroborated by the gene expression data (F= 0.007, P= 0.936). Overall, our results indicate that (1) level of GOX production is not induced by exogenous infections in honey bees and may be an example of how mechanisms of individual immune defense can be co-opted to function as an immune mechanism at the colony level, and (2) GOX assays may not be suitable as a general biomarker of social immunity.