Profiling of the Guadalupe Fur Seal (Arctocephalus philippii townsendii) Fecal Bacteriome in Relation to Alopecic Syndrome.

Alopecic syndrome in Guadalupe fur seals, Arctocephalus philippii townsendii (GFSs), was first observed a decade ago, coinciding with an anomalous warm sea surface temperature event and shifts in foraging behaviors of otariid pinnipeds from Mexican North Pacific colonies. With no evidence of dermatophytes or ectoparasites commonly associated with alopecia, it has been proposed that nutritional or metabolic changes, secondary to altered foraging, may increase the risk of alopecia. We employed 16S rRNA gene deep sequencing to investigate changes in the fecal bacteriome of GFS with and without alopecia. We found no significant differences in species richness nor Simpson's diversity index, and alopecia accounted for less than 6% of the variation in bacteriome structure. However, five bacterial phyla (Bacteroidota, Firmicutes, Fusobacteriota, Proteobacteria, and Spirochaetota) were overrepresented, and two (Actinobacteriota and Campylobacterota) were underrepresented, in GFSs with alopecia. At the genus level, animals with alopecia had a higher abundance of various bacteria, including Parabacteroides, Bacteroides, Lachnospiraceae, Roseburia, and genera within Erysipelotrichaceae, which have been linked to alopecia in humans. The GFS fecal bacteriome revealed 322 distinct bacterial functional pathways, of which 163 varied significantly between cases and controls. The most prominent differences found in GFSs with alopecia were overrepresentation of critical precursors for bacterial cell wall components, aromatic amino acid biosynthesis and pantothenate and CoA biosynthesis, and underrepresentation of glucosyltransferases and bacterial surface antigens, nitrogen and sulfur metabolism, and bacterial secretion systems. Our study provides preliminary evidence that changes in enteric microbiota may contribute to the pathogenesis of alopecia in GFSs via three main mechanisms: dysregulation of immune modulation and sustained inflammation, altered metabolism, and reduced redox balance and detoxification in the gut. While future studies need to explore these possibilities, our findings offer insight into the role of the microbiome in emerging pathologies of wildlife.