Natural Process Art Competitions!
I'm currently aware of 5 such competitions, in various categories, but if you know of others please comment! These mostly announce winners at the beginning-end of the year, although their submission dates are 1-2 months earlier. Check the links for the dates if you are interested in entering, and watch here for me to cover the winners when they are announced!
The winner of the ASM Agar Art Competition for 2021 pictured above was made by Sonja Borndörfer, Norbert W. Hopf and Michael Lanzinger from University of Applied Sciences Weihenstephan-Triesdorf in Freising, Germany, and it is entitled "Microlilies". The color was grown on cystine-lactose-electrolyte-deficient (CLED) agar plates, and drawn with Rhodococcus rhodochrous, an orange appearing bacterium.
https://asm.org/Events/ASM-Agar-Art-Contest/Previous-Winners/2021