Honey bees collect and apply plant resins to the interior of their nest cavity, in order to form a layer around the nest cavity called a propolis envelope. Propolis displays antimicrobial activity against honey bee pathogens, but the effect of propolis on the honey bee microbiome is unknown. Honey bees do not intentionally consume propolis, but they do manipulate propolis with their mouthparts. Because honey bee mouthparts are used for collecting and storing nectar and pollen, grooming and trophallaxis between adults, feeding larvae, and cleaning the colony, they are an important interface between the bees’ external and internal environments and serve as a transmission route for core gut bacteria and pathogens alike. We hypothesized that the antimicrobial activity of an experimentally applied propolis envelope would influence the bacterial diversity and abundance of the worker mouthpart microbiome. The results revealed that the mouthparts of worker bees in colonies with a propolis envelope exhibited a significantly lower bacterial diversity and significantly higher bacterial abundance compared to the mouthparts of bees in colonies without a propolis envelope. Based on the taxonomic results, the propolis envelope appeared to reduce pathogenic or opportunistic microbes and promote the proliferation of putatively beneficial microbes on the honey bee mouthparts, thus reinforcing the core microbiome of the mouthpart niche.

Production of bacterial flagella is controlled by a multi-tiered regulatory system that coordinates expression of 40-50 subunits and ordered assembly of these elaborate structures. Flagellar expression is environmentally controlled, presumably to optimize the benefits and liabilities of having these organelles with cell growth and survival. We recently reported a global survey of AlgU-dependent regulation and binding in pv. DC3000 that included evidence for strong down-regulation of many flagellar and chemotaxis motility genes. Here, we returned to those data to look for other AlgU-dependent influences on the flagellar regulatory network. We identified an AlgU-dependent antisense transcript expressed from within the gene, the master regulator of flagellar biosynthesis in We tested whether expression of this antisense RNA influenced bacterial behavior and found that it reduces AlgU-dependent down-regulation of motility. Importantly, this antisense expression only influenced motility under conditions in which AlgU was expressed. Comparative sequence analysis of the locus containing the antisense transcript's AlgU-dependent promoter in over 300 genomes revealed sequence conservation in most strains that encode AlgU. This suggests that the antisense transcript plays an important role that is conserved across most of the genus. are globally distributed host-specific bacterial pathogens that cause disease on a wide-range of plants. An elaborate gene expression regulation network controls flagella production, which is important for proper flagella assembly and a key aspect of certain lifestyle transitions. pv. DC3000 uses flagella powered motility in the early stages of host colonization and adopts a sessile lifestyle after entering plant tissues, but the regulation of this transition is not understood. Our work demonstrates a link between regulation of motility and global transcriptional control that facilitates bacterial growth and disease in plants. Additionally, sequence comparisons suggest that this regulation mechanism is conserved in most of the genus.