Isolation and characterization of a Nocardiopsis sp. from honeybee guts

Although actinomycetes are the plant-associated environmental bacteria best known for producing thousands of antibiotics, their presence in the guts of flower-feeding honeybees has rarely been reported. Here, we report on the selective isolation of actinomycetes from the gut microbiota of healthy honeybees, and their inhibitory activity against honeybee indigenous bacteria. More than 70% of the sampled honeybees (N > 40) in a season carried at least one CFU of actinomycete. The isolates from bees of one location produced inhibitory bioactivities that were almost exclusively against several bee indigenous Bacillus strains and Gram-positive human pathogens but not Escherichia coli. An antibiotic-producing actinomycete closely related to Nocardiopsis alba was isolated from the guts in every season of the year. A DNA fragment encoding a homologous gene (phzD) involved in phenazine biosynthesis was identified in the isolate. Expression of the phzD detected by reverse transcription-PCR can explain the survival of this organism in anaerobic environments as some redox-active extracellular phenazines are commonly regarded as respiratory electron acceptors. The results raise important questions concerning the roles of the antibiotic-producing actinomycetes and the phenazine-like molecules in honeybee guts and honey.