RCA 1-binding glycans as a marker of Batrachochytrium salamandrivorans infection intensity at early stages of pathogenesis

The fungal skin disease chytridiomycosis threatens global amphibian biodiversity. Among the two causative pathogens, Batrachochytrium dendrobatidis and B. salamandrivorans, the latter has decimated several European salamander populations. However, responses to exposure vary notably across species and individuals, suggesting that understanding the mechanisms behind these variations could enable successful mitigation in surviving populations. A recent study reported that the concentration of epidermal galactose predicts B. salamandrivorans susceptibility at the species level. Here, we used comparative lectin histochemistry with nine lectins to observe lectin staining brightness in the skin and examine its association with the susceptibility of four urodelan species with differential responses to B. salamandrivorans. Subsequently, we exposed Pleurodeles waltl individuals to B. salamandrivorans to assess whether this correlation extends to the individual level. In our study, the degree of labelling with the lectin, Ricinus communis agglutinin I (RCA 1), emerged as the distinctive marker of susceptibility in that resistant species showed minimal RCA 1 binding, while susceptible species exhibited higher levels. Results of the infection trial further demonstrated that an increase in staining brightness correlates with steeper infection slopes at initial stages of infection. This demonstrates RCA 1-binding glycans as a biomarker for individual susceptibility and presents the basis for marker-assisted selection in P. waltl.