There's some discussion here about DNA-specific compression algorithms.

I thought I'd raise yesterday's HN discussion on 'The unreasonable effectiveness of modern sort algorithms' https://news.ycombinator.com/item?id=45208828

That blog post isn't about DNA per se, but it is about sorting data when you know there are only 4 numbers. I guess DNA has 5 - A,T,G,C,N the unknown base - but there's a huge space of DNA-specific compression research that outperforms ZSTD.