Apple Tree by Dr. Niall Hamilton of New Zealand. Source.
Curious about what all you can paint using bacteria as your pigments? Use your artistry to inoculate agar plates by design, then wait for the bacteria to grow into colonies in esthetic shapes and colors. To whet your appetite and see what can be done, given appropriate talent, visit Microbial Art at http://www.microbialart.com/ Here you'll find original works grown by several microbiologists of artistic bent.
This website, the creation of T. Ryan Gregory at the University of Guelph, has links to lots of other visual goodies. There's almost no end to them.