Genome Scientists Found Evolutionary Benefit to Harmful Fungus Batrachochytrium Salamandrivorans

Scientists have found that a fungus that infects salamanders has multiple copies of the same transposons, also known as jumping genes. These genes can replicate themselves and influence the organism, but having too many of them can be harmful. Many organisms have repeated sections of DNA, including some jumping genes, but they have systems in place to prevent or limit the negative effects of having too many.

The MRC Centre for Medical Mycology at the University of Exeter has conducted a study that suggests the jumping genes found in the fungus Batrachochytrium salamandrivorans (Bsal) may have an evolutionary advantage. The study found multiple copies of different versions of these jumping genes in Bsal's genome. Additionally, the researchers discovered that the gene in question had duplicated another group of genes contributing to the infection's severity in fire salamanders.

Fungus Affecting Salamander Skin

As reported by News Medical, Bsal is a fungus that infects the skin of salamanders and newts, leading to the development of severe wounds. It was originally found in Asia, where some newts and salamanders have a degree of resistance to it. However, it has since spread to Europe, causing a decline in salamander populations there. The researchers used advanced sequencing techniques to discover that Bsal had undergone genome expansion compared to similar species. This means that it has a larger genome with more genes and a higher number of transposons, also known as "jumping genes."

The study found that the transposons' ability to replicate themselves played a significant role in this genome expansion. According to the researchers, transposons can be thought of as multiple copies of the same page in an organism's genome, which contributes to the overall size of the genome.

The researchers found that the process of copying and pasting caused by repetitive transposons also amplified certain genes contributing to the salamanders' skin destruction. This makes the fungus more deadly, as it can destroy the skin of the salamanders more quickly. Duplicative DNA, including jumping genes, is occasionally directed to as "junk" DNA.

'Paradigm Shift' of the Study

According to the study's senior author, Dr. Rhys Farrer, most organisms have a small number of transposons, and in humans, they make up less than 1% of the genome. There are also mechanisms in place to prevent this number from increasing. However, in Bsal, repeated jumping genes make up about 19% of the genome. While transposons can disrupt the normal function of genes and cause problems for the organism, it appears that the benefits outweigh the risks for Bsal. The research team is continuing to study this topic.

Dr. Farrer said this type of gene repetition might be more common than previously thought. If it gives the pathogen an evolutionary advantage by making it more virulent, as seems to be the case with Bsal, it's unclear why this isn't more widespread.

This study provides new insights into the evolution of the major amphibian disease and represents a "paradigm shift" in understanding repetitive genome content as a key factor in the pathobiology of the disease. The scientists included researchers from the Imperial College of London, and the Wellcome Trust supported the study. The study was published in the online journal PNAS.

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