No one likes to be in crowded spaces, so when colonies reach a critical cell density, cells within the colony begin to lyse, dramatically changing the architecture of the colony. The colony on the left is a wild-type colony, while the colony on the right is a genetic mutant that exhibits an autolytic phenotype, that is the bacterium’s own enzymes “eat up” its cells. The translucence of the colony indicates cell death, and the striations are created as surface cells fight for resources. This appearance can be explained by the toxic overproduction of a signaling molecule called Pseudomonas Quinolone Signal (PQS) that help the bacteria in the colony count the number of neighboring cells.
Contributed by Ian Hill, a fifth year graduate student in the Biological and Biomedical Sciences program at Harvard University, and our Featured Artist for January and February, 2018. To meet Ian and see more of his art, click here.