This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: When scientists study bacteria that are not in a Petri dish or a test tube but in environments that more closely mimic their actual microbial habitats, they often find delightfully unexpected behaviors. For Sujit Datta, a professor of chemical engineering, bioengineering and biophysics at Caltech, those oddities are an invitation to apply physics to exciting new puzzles.
The results reveal previously unknown ways in which bacteria organize themselves and interact with their surroundings, and suggest new questions about how the shape of bacterial colonies affects their ability to survive, grow and even resist treatment. Recently, Datta and his former graduate student Sebastian Gonzalez La Corte looked at bacteria growing in liquid crystal fluids—those whose molecules are elongated and all point in the same direction. This aligned state is known to occur in some biological fluids, such as certain biofilm matrices and mucus linings of the airways and gut, yet laboratory experiments typically study bacteria in fluids whose constituents have no preferred direction.
Once again, the team made some unexpected observations. The findings are described in a paper in the journal PNAS. Datta's group previously studied and modeled bacterial growth in polymeric fluids with randomly arranged molecules.
In that setting, the team found that several commonly studied bacterial species, including Escherichia coli, Vibrio cholerae (the pathogen that causes cholera) and Pseudomonas aeruginosa (a species that often causes infections in immunocompromised or hospitalized patients), grow into long cables, several cells wide, that intertwine and form a kind of "living gel." In contrast, the new work shows that in an aligned liquid crystal fluid, bacteria build single-cell-wide chains that grow and lengthen in relatively straight lines until they suddenly buckle in an unexpected way. When a steel beam is compressed on either end, it eventually buckles, bending gradually in an arc-like fashion along its entire length. But when the "beam" is made of bacteria in a liquid crystal fluid, its buckling is localized—with only a small section bending very tightly.
Why would these bacterial beams behave so differently? "This is a weird mechanics problem. Mechanicians have thought about thin, slender beams buckling for decades," Datta says.
"But this is an odd version of that problem because this beam is made out of cells that are self-replicating." Datta and his colleagues collaborated with applied mathematicians at the University of Wisconsin–Madison and the University of North Carolina at Chapel Hill to build a mathematical model of bacterial growth in liquid crystals. To understand the system, Datta says, consider the metaphor of matches in a matchbox: The matches are the aligned liquid crystal molecules. Now imagine introducing a bacterium into the system; the bacterial cell, which is much larger than the liquid crystals, could be represented by a pencil in a very large matchbox.
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