Browsing by Author "Li, Dong"

Now showing 1 - 4 of 4
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    A de novo matrix for macroscopic living materials from bacteria
    (Springer Nature, 2022) Molinari, Sara; Tesoriero, Robert F.; Li, Dong; Sridhar, Swetha; Cai, Rong; Soman, Jayashree; Ryan, Kathleen R.; Ashby, Paul D.; Ajo-Franklin, Caroline M.
    Engineered living materials (ELMs) embed living cells in a biopolymer matrix to create materials with tailored functions. While bottom-up assembly of macroscopic ELMs with a de novo matrix would offer the greatest control over material properties, we lack the ability to genetically encode a protein matrix that leads to collective self-organization. Here we report growth of ELMs from Caulobacter crescentus cells that display and secrete a self-interacting protein. This protein formed a de novo matrix and assembled cells into centimeter-scale ELMs. Discovery of design and assembly principles allowed us to tune the composition, mechanical properties, and catalytic function of these ELMs. This work provides genetic tools, design and assembly rules, and a platform for growing ELMs with control over both matrix and cellular structure and function.
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    Assessing Biological Interactions and Potential Impacts of Emerging Carbonaceous Materials to Terrestrial Organisms
    (2011) Li, Dong; Alvarez, Pedro J.
    This research addresses the potential ecotoxicity of two emerging carbonaceous materials: C 60 and biochar. The use of these materials is rapidly increasing, as well as their potential for widespread applications. Thus, information about unintended consequences associated the widespread use, incidental or accidental release, and disposal of these emerging materials is needed. The environmental impacts of C 60 , its stable water suspension (nC 60 ), and biochar are assessed here using bacteria and earthworms as model receptors. The antibacterial activity of nC 60 can be mitigated by the presence of natural organic matter as a soil constituent or dissolved in the water column. Sorption to soil might decrease the bioavailability of nC 60 and thus its toxicity to bacteria. Aqueous organic matter also may mitigate nC 60 toxicity. Pristine C 60 showed toxicity to the earthworm's reproduction and was rapidly bioaccumulated by earthworms, although to a lower extent than smaller phenanthrene molecules that are more hydrophobic; thus, the large molecular size of C 60 hinders its bioaccumulation. Less bioaccumulation occurred at higher C 60 concentration in soil, which is counterintuitive and reflects that higher C 60 concentrations that exceed the soil sorption capacity exist as larger precipitates that are less bioavailable. Earthworms avoided soils amended with high concentrations of dry biochar, and experienced significant weight loss after 28-day exposure. The avoidance response was likely to avert desiccation rather than to avoid potential toxicants (i.e., PAHs formed during biochar production by pyrolysis) or nutrient scarcity. By wetting the biochar to field capacity before exposing the worms, this adverse effect can be completely mitigated. Overall, this research provides a foundation for ecotoxicity assessment associated with exposure to C 60 or biochar, and establishes a method by which other emerging materials can be evaluated for their potential environmental impacts.
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    Effect of geosorbents on the antibacterial activity of nC60
    (2008) Li, Dong; Alvarez, Pedro J.
    The rapid development of nanotechnology calls for a timely assessment of the impact of manufactured nanoparticles on environmental settings. This study investigated the association between a C 60 water suspension (nC 60 ) and geosorbents, and their effects on the antibacterial activity of C 60 . The presence of geosorbents reduced the bioavailability of nC 60 and thus its antibacterial activity. Adsorption of humic acid onto nC 60 was also found to eliminate nC 60 toxicity, probably due to coating of nC 60 , which hinders its direct contact with bacteria. These findings indicate the toxicity of nC 60 is controlled by its bioavailability in natural soil settings.
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    Engineering High-Yield Biopolymer Secretion Creates an Extracellular Protein Matrix for Living Materials
    (American Society for Microbiology, 2021) Orozco-Hidalgo, Maria Teresa; Charrier, Marimikel; Tjahjono, Nicholas; Tesoriero, Robert F.; Li, Dong; Molinari, Sara; Ryan, Kathleen R.; Ashby, Paul D.; Rad, Behzad; Ajo-Franklin, Caroline M.
    The bacterial extracellular matrix forms autonomously, giving rise to complex material properties and multicellular behaviors. Synthetic matrix analogues can replicate these functions but require exogenously added material or have limited programmability. Here, we design a two-strain bacterial system that self-synthesizes and structures a synthetic extracellular matrix of proteins. We engineered Caulobacter crescentus to secrete an extracellular matrix protein composed of an elastin-like polypeptide (ELP) hydrogel fused to supercharged SpyCatcher [SC(−)]. This biopolymer was secreted at levels of 60 mg/liter, an unprecedented level of biomaterial secretion by a native type I secretion apparatus. The ELP domain was swapped with either a cross-linkable variant of ELP or a resilin-like polypeptide, demonstrating this system is flexible. The SC(−)-ELP matrix protein bound specifically and covalently to the cell surface of a C. crescentus strain that displays a high-density array of SpyTag (ST) peptides via its engineered surface layer. Our work develops protein design guidelines for type I secretion in C. crescentus and demonstrates the autonomous secretion and assembly of programmable extracellular protein matrices, offering a path forward toward the formation of cohesive engineered living materials. IMPORTANCE Engineered living materials (ELM) aim to mimic characteristics of natural occurring systems, bringing the benefits of self-healing, synthesis, autonomous assembly, and responsiveness to traditional materials. Previous research has shown the potential of replicating the bacterial extracellular matrix (ECM) to mimic biofilms. However, these efforts require energy-intensive processing or have limited tunability. We propose a bacterially synthesized system that manipulates the protein content of the ECM, allowing for programmable interactions and autonomous material formation. To achieve this, we engineered a two-strain system to secrete a synthetic extracellular protein matrix (sEPM). This work is a step toward understanding the necessary parameters to engineering living cells to autonomously construct ELMs.