Cover image by Melanie Pearson
Proteus mirabilis, a common agent of catheter-associated urinary tract infection, is famed for its ability to swarm over agar surfaces in a characteristic bullseye pattern. In this image, a guaA mutant displays a strikingly altered pattern of swarming motility. P. mirabilis mutants with altered swarming motility are often also impaired in virulence, as is the case for this mutation in
GMP synthase, which renders the organism auxotrophic for guanosine. Purine biosynthesis was one of several key fitness factors identified using an ordered library screen on agar made from homogenized mouse organs or human urine (that is, “organ agar”).
