Zeta-potential of Nosema spp. spores under standardized conditions

The microsporidian parasites Nosema apis and Nosema ceranae cause nosemosis in honey bees, and spore surface charge is expected to influence adhesion and colloidal stability. However, zeta-potential (ζ) data for Nosema spores are absent from the literature. Here we report the first electrophoretic light-scattering measurements of ζ for N. ceranae spores under standardized conditions (10 mM KCl, pH 7.0, 25 °C). Spores were purified by differential centrifugation and analyzed in ten technical replicates. The mean ζ was -45.2 ± 1.8 mV (coefficient of variation 4.0%). The intensity-weighted distribution was unimodal with a peak at -42.5 mV, and autocorrelation functions indicated good data quality. The pH-dependence curve yielded a point of zero charge at pH 4.8, with a steep negative shift above pH 5, implying that surface carboxyl and phosphate groups dominate the charge. At the pH of the honey-bee midgut (6.0-6.5), ζ is estimated as -20 to -30 mV, which may permit moderate aggregation and influence infection efficiency. The high repeatability (σ = ± 1.8 mV) validates electrophoretic light scattering for future screening of anti-nosemal agents.