String Theory: How bacterial growth is influenced by ionic interactions

Bacteria often grow in saline environments such as tissues/gels in hosts and bodies of water (e.g., salty lakes, marshes, and the ocean) in the environment. While lab studies typically focus on bacterial cells in idealized solutions of primarily monovalent salts, these saline environments often have an abundance of multivalent ions. Hence, we ask: How do multivalent ions change how bacteria grow?

Here, we report that at sufficiently high concentrations of divalent salts, immotile E. coli do not grow as random dispersions of disconnected cells, as in the monovalent salt case; instead, they grow into string-like colonies comprising single cells arranged end-to-end. We conjecture that this unusual colony morphology arises due to divalent cation-mediated crosslinking of lipopolysaccharides at the surface of adjacent cells after division. Such morphological structures could have major biological implications in the efficiency and patterning of gene transfer and propagation of bacteriophages through bacterial populations.