A near-complete telomere-to-telomere genome assembly for Batrachochytrium dendrobatidis GPL JEL423 reveals a larger CBM18 gene family and a smaller M36 metalloprotease gene family than previously recognised.

Batrachochytrium dendrobatidis (Bd) is responsible for mass extinctions and extirpations of amphibians, mainly driven by the Global Panzootic Lineage (BdGPL). BdGPL isolate JEL423 is a commonly used reference strain in studies exploring the evolution, epidemiology and pathogenicity of chytrid pathogens. These studies have been hampered by the fragmented, erroneous and incomplete B. dendrobatidis JEL423 genome assembly, which includes long stretches of ambiguous positions, and poorly resolved telomeric regions. Here we present and describe a substantially improved, near telomere-to-telomere genome assembly and gene annotation for B. dendrobatidis JEL423. Our new assembly is 24.5 Mb in length, ∼800 kb longer than the previously published assembly for this organism, comprising 18 nuclear scaffolds and 2 mitochondrial scaffolds and including an extra 839 kb of repetitive sequence. We discovered that the patterns of aneuploidy in B. dendrobatidis JEL423 have remained stable over approximately 5 years. We found that our updated assembly encodes fewer than half the number of M36 metalloprotease genes predicted in the previous assembly. In contrast, members of the crinkling and necrosis gene family were found in similar numbers to the previous assembly. We also identified a more extensive carbohydrate binding module 18 gene family than previously observed. We anticipate our findings, and the updated genome assembly will be a useful tool for further investigation of the genome evolution of the pathogenic chytrids.