Genes-to-Gels: Toughness and Resilience of Biofilm-enabled Materials

This project seeks to develop novel biofilm-enabled materials, including double-network hydrogels containing EPS networks for greater toughness and resilience. Previous mechanical studies have focused nearly exclusively on medically-relevant bacteria or consortia producing bacterial cellulose, leaving largely unexplored the material properties of diverse bacterial biofilms that have proved resilient and evolutionarily successful across wide fluctuations in environmental conditions. Our target biofilm for this project is a macroscopic bacterial aggregate that has been the focus of previous ICB Systems and Synthetic Biology investigations: the “pink berry” consortia. These fast-settling aggregates, found abundantly throughout the year at the sediment-water interface of the salt marshes of the Woods Hole, Massachusetts area, display remarkable survival across broad operating temperatures from 4 - 45°C. Prior ICB-funded work has generated a comprehensive genomic catalog of the pink berry microbiome, which is dominated by three distinct species: (1) sulfide-oxidizing, phototrophic purple sulfur bacteria from the Chromatiales, which grow in dense, pink, tubule-like microcolonies surrounded by clear EPS; (2) sulfate reducing bacteria (green cells, and (3) purple nonsulfur bacteria from the Rhodobacteraceae. Rapid bacterial respiration maintains anoxia at the core of the pink berry aggregates even in fully oxygenated environments and creates microniches for both aerobic and anaerobic metabolism, analogous to the millimeter-sized granules in one-step upflow sludge reactors that combine aerobic nitrification and anaerobic ammonia oxidation (anammox) for ammonia removal. Though as-of-yet-uncultured, the consortia has been well-described using an integrated suite of microscopy and microscale geochemical tools.

We will quantify the mechanical properties (e.g., elastic modulus, poroelasticity, stress relaxation, and fracture mechanics) of native pink berry aggregates using our custom-built in situ microindentation tools. 

Additionally, we will investigate the relaxation rates of EPS networks in pink berry aggregates to determine their role in time-dependent mechanical and rheological responses of diverse biofilms. This understanding will enable us to impart synthetic hydrogels doped with EPS networks with controllable time-dependent relaxation properties.