Arranging Bacteria In 3-D

Bacteria live in a three-dimensional environment, but scientists don’t have a good way to define the shape of environments in the lab. To achieve that control, Jason B. Shear and coworkers at the University of Texas, Austin, use multiphoton lithography, a 3-D printing technique, to sculpt the bacterial environment into a variety of 3-D shapes (Proc. Natl. Acad. Sci. USA 2013, DOI: 10.1073/pnas.1309729110). In this method, they first suspend the bacteria in gelatin mixed with a photosensitive molecule that promotes cross-linking between polypeptides in the gelatin. Next, they use multiphoton excitation with 740-nm light to initiate the cross-linking and create containers around the bacteria in a variety of configurations—adjacent, nested, or free-floating. Finally, they culture the bacteria inside the containers until they reach the desired density. Although the bacteria are fully enclosed, the porous gelatin easily transmits biologically active molecules, such as those required for bacterial signaling. In a model system, naturally susceptible Staphylococcus aureus display resistance to the β-lactam ampicillin when they are nested within a layer of Pseudomonas aeruginosa, which produce enzymes that degrade β-lactams, the researchers report.