Should I mention in a PhD application statement of purpose that I earn a large income from a business I created?
No, don't mention income here. This just looks smug. But ofc you should mention that you are running a successfull buisness and explain how this can contribute to your Phd (experience, skills,...). The problem I see is that you want to do a microbiology PhD while running your own buisness? This could be a big problem because they don't want to fund people who are not 100% focused on their work here.