Ory, F. | bioRxiv Science

bioRxiv2025

Ecology and pathogenicity for honey bee brood of recently described Paenibacillus melissococcoides and comparison with Paenibacillus dendritiformis, Paenibacillus thiaminolyticus

Honey bee colonies contain thousands of individuals living in close proximity in a thermally homeostatic nest, creating ideal conditions for the thriving of numerous pathogens. Among the bacterial pathogens, Paenibacillus larvae infects larvae via the nutritive jelly that adult workers feed them, causing the highly contagious American foulbrood disease. Further Paenibacillus species were anecdotally found in association with honey bees, including when affected by another disease, European foulbrood (EFB). However, their pathogenicity remains largely unknown. Our results indicate that Paenibacillus dendritiformis, Paenibacillus thiaminolyticus and newly described Paenibacillus melissococcoides are pathogenic towards honey bee brood and that their virulence correlates with their sporulation ability, which confers them resistance to the bactericidal properties of the nutritive jelly. Our survey occasionally but increasingly detected P. melissococcoides in confirmed and idiopathic cases of EFB but never in healthy colonies, suggesting that this bacterium is an emerging pathogen of honey bee brood. Overall, our results suggest that virulence traits allowing a pathogenic or opportunistically pathogenic habit towards honey bee brood are frequent in Paenibacillus spp., but that their degree of adaptation to this host varies. Our study clarifies the ecology of this ubiquitous genus, especially when infecting honey bees.

microbiology↗

bioRxiv2020

Potassium channels, megapolarization, and water pore formation are key determinants for cationic cell-penetrating peptide translocation into cells

Cell-penetrating peptides (CPPs) allow intracellular delivery of cargo molecules. They provide efficient methodology to transfer bioactive molecules in cells, in particular in conditions when transcription or translation of cargo-encoding sequences is not desirable or achievable. The mechanisms allowing CPPs to enter cells are ill-defined. Using a CRISPR/Cas9-based screening, we discovered that KCNQ5, KCNN4, and KCNK5 potassium channels positively modulate cationic CPP direct translocation into cells by decreasing the transmembrane potential (Vm). These findings provide the first unbiased genetic validation of the role of Vm in CPP translocation in cells. In silico modeling and live cell experiments indicate that CPPs, by bringing positive charges on the outer surface of the plasma membrane, decrease the Vm to very low values (-150 mV or less), a situation we have coined megapolarization that then triggers formation of water pores used by CPPs to enter cells. Megapolarization lowers the free energy barrier associated with CPP membrane translocation. Using dyes of varying sizes, we assessed the diameter of the water pores in living cells and found that they readily accommodated the passage of 2 nm-wide molecules, in accordance with the structural characteristics of the pores predicted by in silico modeling. Pharmacological manipulation to lower transmembrane potential boosted CPPs cellular internalization in zebrafish and mouse models. Besides identifying the first proteins that regulate CPP translocation, this work characterized key mechanistic steps used by CPPs to cross cellular membrane. This opens the ground for strategies aimed at improving the ability of cells to capture CPP-linked cargos in vitro and in vivo.

cell biology↗