Intestinal microbial diversity in domestic honey bees and evaluation of their probiotic properties

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As populations of managed honey bees in various regions increase in comparison to wild colonies, there is a need to ensure that threats to bee health and survival in all environments are countered. One of the more direct methods of approaching bee health is through dietary means and as such, we investigated the intestinal microbial diversity in the gut of honey bees in order to identify strains with probiotic potential. Honey bees were fed with several feeds including Feedbee, Megabee, sugar syrup 60% (w/v), Yangbongnonghyup (YBNH), and Test A, to monitor the culture-dependent and culture-independent microbial diversity. In the culture-dependent study, most isolates belonged to Apilactobacillus (24.1%), Fructobacillus (21.8%), and Bacillus (15.4%) at the genus level. Culture-independent results showed that Bacillota and Pseudomonadota were the most abundant groups (99%) among the gut bacteria, while other bacteria showed a lower percentage than 0.1%. Next, the hydrolytic enzymes (α-amylase, protease, and cellulase) and antibacterial and antioxidant activities of the isolated strains were evaluated to examine their applicability as potential probiotics for honey bees. The selected strains showing three hydrolytic enzyme activities were used to determine their antibacterial activity against Paenibacillus larvae. Bacillus subtilis MBLB2796 showed the highest α-amylase (1.24 ± 0.06 U/mL) and cellulase (0.24 ± 0.01 U/mL) activities while B. tequilensis MBLB2834 exhibited the highest protease activity (0.15 ± 0.03 mU/mL) and the highest antioxidant activity (71.0 ± 3.8%). This study suggests that honey bee gut-originated isolates are prime candidates for use as probiotics in honey bees.