Host Specificity of Snodgrassella in Eastern and Western Honeybees and Its Effects on Naturally Occurring Deformed Wing Virus Titers

Honeybee gut microbiota undergoes long-term adaptive evolution with the host, resulting in host-specific genomic and functional characteristics. However, the specific role of host-specialized strains in shaping host physiological functions remains understudied. This study investigates the host specificity of the core gut symbiont <i>Snodgrassella</i> in <i>A. cerana</i> and <i>A. mellifera</i>, exploring its effects on immune response and natural virus suppression through genomic analysis and colonization experiments. Genomic analysis revealed that strain from <i>A. mellifera</i>, exhibited a larger genome and greater gene content compared to strain from <i>A. cerana</i>. Competitive colonization experiments showed that although strains from different origins had similar colonization efficiency in the host, host-specific strain displayed a clear home-field advantage in the competitive colonization process. Moreover, Inoculation of <i>A. mellifera</i> with its native <i>Snodgrassella</i> strain significantly reduced Deformed Wing Virus (DWV) titers, whereas a non-native strain had no effect. In contrast, neither strain altered DWV or Sacbrood Virus (SBV) levels in <i>A. cerana</i>. Immune gene analysis revealed that only the native <i>Snodgrassella</i> strain upregulated <i>defensin 2</i> in <i>A. mellifera</i>, while no significant changes occurred in <i>A. cerana</i> with either strain. These results suggest that <i>Snodgrassella</i> exhibits host specificity at the strain level, influencing both host immune response and virus suppression, with non-native strains showing reduced efficacy in these functional roles, especially in <i>A. mellifera</i>.