Modulation of Biofilm Mechanics by DNA Structure and Cell Type.

Deoxyribonucleic acid (DNA) evolved as a tool for storing and transmitting genetic information within cells, but outside the cell, DNA can also serve as "construction material" present in microbial biofilms or various body fluids, such as cystic fibrosis, sputum, and pus. In the present work, we investigate the mechanics of biofilms formed from <i>Pseudomonas aeruginosa</i> Xen 5, <i>Staphylococcus aureus</i> Xen 30, and <i>Candida albicans</i> 1408 using oscillatory shear rheometry at different levels of compression and recreate these mechanics in systems of entangled DNA and cells. The results show that the compression-stiffening and shear-softening effects observed in biofilms can be reproduced in DNA networks with the addition of an appropriate number of microbial cells. Additionally, we observe that these effects are cell-type dependent. We also identify other mechanisms that may significantly impact the viscoelastic behavior of biofilms, such as the compression-stiffening effect of DNA cross-linking by bivalent cations (Mg²⁺, Ca²⁺, and Cu²⁺) and the stiffness-increasing interactions of <i>P. aeruginosa</i> Xen 5 biofilm with Pf1 bacteriophage produced by <i>P. aeruginosa</i>. This work extends the knowledge of biofilm mechanobiology and demonstrates the possibility of modifying biopolymers toward obtaining the desired biophysical properties.