By day, Melinda Grosser, an assistant professor of biology at the University of North Carolina (UNC) Asheville, teaches undergraduate students introductory biology and advanced microbiology, while conducting her own research on Staphylococcus aureus physiology. But when the students go home, Grosser gets out her agar plates and brightly-colored bacteria collection to make literature-based agar art.
Posting on Instagram as @thebookishbacteriologist, Grosser displays petri dishes that recreate the covers of her latest reads. She combines each image with a book review and a microbiology fact—or, “Bacteriophact”—that relates to the book’s themes. “It's a fun way to share science, microbiology facts, with people who might not be seeking out science accounts, but they like to read,” said Grosser.
Creating agar art is not a simple task since the bacterial “paint” is nearly invisible upon application. “I usually draw out what I want to do on a piece of paper first, and then I'll tape the petri dish onto it so I can trace an outline,” Grosser explained. After filling in the outline with bacteria that express different pigments as they grow, she incubates them until the microbes pack the plate, revealing the bookish images.
Birnam Wood by Eleanor Catton
Staphylococcus saprophyticus (white), Janthinobacterium lividum (dark purple), and Serratia marcescens (red) are naturally-pigmented bacteria. Grosser grew these microbes on tryptic soy agar plates by incubating them for five days at room temperature. “It is actually really hard to keep colors separate and not cross contaminate them when I'm covering the whole plate,” said Grosser. Even a single cell of the fast-growing S. marcescens placed incorrectly will result in a big red splotch tarnishing the final picture, so Grosser made sure to add that one last. “I also left gaps between adjacent strains of bacteria when inoculating, but the J. lividum and S. marcescens are both quite motile and spread to fill them in,” Grosser added. “The blended colors worked for this particular piece!”
House of Mirth by Edith Wharton
For some colors, naturally-pigmented bacteria that play nicely in the laboratory are difficult to find. In these cases, Grosser uses bacteria engineered to produce chromoproteins from Amino Labs—a company that sells agar art kits. The pink color in this plate comes from E. coli expressing a magenta chromoprotein. So that the E. coli would not outgrow the white S. saprophyticus and purple J. lividum, Grosser decreased the available nutrients by cutting the tryptic soy in the agar in half. This change also produced a light pink color rather than a strong magenta since the E. coli were only just beginning to grow when Grosser imaged the plate.
Anatomy: A Love Story by Dana Schwartz
To mimic the background color of this book cover, Grosser chose a MacConkey agar plate, which contains crystal violet dye and a neutral red pH indicator. Because MacConkey agar allows only Gram-negative bacteria to grow, Grosser drew an anatomical heart using a red pigment-producing S. marcescens strain that was isolated from the North Carolina soil by one of her UNC Asheville students. She also achieved a subtle pink halo around the heart with unpigmented E. coli. These bacteria fermented the lactose in the agar and turned pink due to the pH indicator.
A fictional plague reminiscent of the Black Death caused by Yersinia pestis plays a prominent role in Anatomy: A Love Story. This inspired the Instagram post’s “Bacteriophact,” which schooled Grosser’s readers about the Black Death’s history, including how scientists pieced together which Y. pestis strains likely spread the plague throughout Europe.
Now Is Not the Time to Panic by Kevin Wilson
This book cover agar art for Now Is Not the Time to Panic by Kevin Wilson required a bit of trial and error. Grosser created the green hue on this plate by blending two E. coli strains that produced yellow and blue chromoproteins. The bacteria in the center of the letters were tightly packed, with yellow and blue cells evenly mixed to give the appearance of a green color. Towards the edges, individual cells had room to grow into distinct yellow and blue colonies. “While this is not my neatest work or most complex design, I love the way the colors turned out,” said Grosser.
To provide optimal growth conditions for the E. coli, Grosser initially grew this plate at 37°C, but this temperature killed the soil strain of J. lividum that she used to write the small letters. Realizing her mistake, Grosser reinoculated the purple bacteria and grew the plate again at room temperature until the purple violacein pigment appeared.
