COS 171-3 - Skin peptides inhibit Batrachochytrium fungi from an undescribed Ranidae frog from Panamá

Abstract: Amphibian skin as well as their mucosal secretions contain compounds that can contribute to host defense against emerging diseases. The emerging fungal pathogens Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal) have been causing population declines; however, host or environmental factors are leading to changes in disease dynamics. Interactions between host skin defenses, such as peptides and microbes, play a vital role in host health and could help inhibit the pathogen. Antimicrobial skin peptides and microbiota are crucial components for protecting amphibians from pathogens and could help us determine whether a species will suffer decline due to Bd/Bsal, especially when focusing on a novel species. Our main objectives were to determine the peptide concentration that will inhibit Bd/Bsal growth in vitro and the microbial composition of the frog skin. We focused on an undescribed species from Panamá, previously identified as Lithobates pipiens. Both natural mixtures of skin peptides, and individually synthesized peptides determined with mass spectrometry tested in the inhibition assays with serial dilutions. Bacterial samples were cultured, isolated, and sequenced for taxonomy. Data was analyzed using QIIME2 and R studio.

We focused on 6 unknown peptides, related to Brevinin and Ranateurin peptide families, and 2 Ranateurin ancestral peptides. Peptides from these families are known for their antifungal characteristics. In general, peptides showed greater minimum inhibitory concentration (MIC) at higher uM concentrations; MIC >100uM. Peptides were more efficient at inhibiting Bd than Bsal, even at higher concentrations. Ranateurin related peptides were more efficient since they needed lower MIC to completely inhibit pathogen growth. In general, this could mean that for this species having specific peptides at higher concentration might be ideal to inhibit Bd/Bsal or to prevent pathogen colonization. Understanding the pathogen inhibitory characteristics of a species is crucial since disease dynamics for host and pathogen are constantly changing. Discovering mechanisms of resilience to disease emergence in novel amphibian is critical to conservation and disease mitigation.