Self-induced mechanical stress can trigger biofilm formation in uropathogenic Escherichia coli

Successful treatment of a unique chronic multi-bacterial scalp infection with N-chlorotaurine, N-bromotaurine and bromamine T

Microbial species can act in synergy to circumvent environmental stress conditions and survive. In addition, biofilms are a serious public-health issue globally and constitute a clinical emergency. Infection persistence, increased morbidity and mortality, and antibiotic resistance are consequences of poly-microbial synergy. Due to inherited complexity and synergy between numerous species, newer antimicrobial agents of increased efficacy and tolerability are needed. In this unique medical case, a chronic (9 year) multi-bacterial scalp infection was differentially diagnosed from other inflammatory skin disorders by prolonged microbiological culture. The bacterial species found seem to have caused lesions of visible biofilm not documented previously in the medical literature. This complicated infection was treated successfully and rapidly with the combined topical application of the active halogen compounds N-chlorotaurine, N-bromotaurine and bromamine T, which is in contrast to the previous failed systemic and topical therapeutic approaches. This study strengthens the case for the use of active halogen compounds against multi-bacterial infections of the skin in the future, without the occurrence of resistance.

Precise promoter integration improves cellulose bioconversion and thermotolerance in Clostridium cellulolyticum

Lignocellulose has been used for production of sustainable biofuels and value-added chemicals. However, the low-efficiency bioconversion of lignocellulose greatly contributes to a high production cost. Here, we employed CRISPR-Cas9 editing to improve cellulose degradation efficiency by editing a regulatory element of the cip-cel gene cluster in Clostridium cellulolyticum. Insertion of a synthetic promoter (P4) and an endogenous promoter (P2) in the mspI-deficient parental strain (Δ2866) created chromosomal integrants, P4-2866 and P2-2866, respectively. Both engineered strains increased the transcript abundance of downstream polycistronic genes and enhanced in vitro cellulolytic activities of isolated cellulosomes. A high cellulose load of 20 g/L suppressed cellulose degradation in the parental strain in the first 150 h fermentation; whereas P4-2866 and P2-2866 hydrolyzed 29% and 53% of the cellulose, respectively. Both engineered strains also demonstrated a greater growth rate and a higher cell biomass yield. Interestingly, the Δ2866 parental strain demonstrated better thermotolerance than the wildtype strain, and promoter insertion further enhanced thermotolerance. Similar improvements in cell growth and cellulose degradation were reproduced by promoter insertion in the wildtype strain and a lactate production-defective mutant (LM). P2 insertion in LM increased ethanol titer by 65%. Together, the editing of regulatory elements of catabolic gene clusters provides new perspectives on improving cellulose bioconversion in microbes.

Structured silicon for revealing transient and integrated signal transductions in microbial systems

Bacterial response to transient physical stress is critical to their homeostasis and survival in the dynamic natural environment. Because of the lack of biophysical tools capable of delivering precise and localized physical perturbations to a bacterial community, the underlying mechanism of microbial signal transduction has remained unexplored. Here, we developed multiscale and structured silicon (Si) materials as nongenetic optical transducers capable of modulating the activities of both single bacterial cells and biofilms at high spatiotemporal resolution. Upon optical stimulation, we capture a previously unidentified form of rapid, photothermal gradient-dependent, intercellular calcium signaling within the biofilm. We also found an unexpected coupling between calcium dynamics and biofilm mechanics, which could be of importance for biofilm resistance. Our results suggest that functional integration of Si materials and bacteria, and associated control of signal transduction, may lead to hybrid living matter toward future synthetic biology and adaptable materials.

Synergistic Chemical and Photodynamic Antimicrobial Therapy for Enhanced Wound Healing Mediated by Multifunctional Light-Responsive Nanoparticles

Recently, rapid acquisition of antibiotic resistance, increased prevalence of antibiotic-resistant bacterial infections, and slow healing of infected wound have led to vast difficulties in developing innovative antimicrobial agents to obliterate pathogenic bacteria and simultaneously accelerate wound healing. To effectively solve this problem, we designed light-responsive multifunctional nanoparticles with conjugation of quaternary ammonium chitosan and photosensitizer chlorin e6 (Ce6) to merge chemical and photodynamic therapy to efficient antibacteria. The Mg/(-)-epigallocatechin-3-gallate (EGCG) complex rapidly responded to light irradiation under 660 nm with release of magnesium ions, which effectively accelerated wound healing without toxicity to mammalian cells. Notably, positively charged nanoparticles could efficiently adhere to the bacterial surface, and reactive oxygen species (ROS) produced under laser irradiation destroyed the membrane structure of the bacteria, which is irreversible, ultimately leading to bacteria death. Thus, multifunctional nanoparticles with a combination of chemical and photodynamic antimicrobial therapy would offer guidance to rational predicted and designed new effective antimicrobial nanomaterials. Most importantly, it may represent a promising class of antimicrobial strategy for potential clinical translation.

A comparative study on the cellular viability and debridement efficiency of antimicrobial-based wound dressings

A concentrated surfactant gel containing polyhexamethylene biguanide (CSG-PHMB) (CSG: Plurogel) was evaluated for in vitro cell cytotoxicity using the direct contact, extraction, and cell insert assays, along with its ability to breakdown artificial wound eschar and slough, compared with other clinically available wound gels: a wound gel loaded with 0.13% benzalkonium chloride (BXG) and a highly viscous gel loaded with 0.1% polyhexamethylene biguanide (PXG). Following treatment with CSG-PHMB, BXG, and PXG at day 1, the viability of L929 and HDFa cells sharply decreased to lower than 20% of the culture media control in the direct contact assay; however, cell viability of L929 was 128.65 ± 1.41%, 99.90 ± 2.84%*, and 64.08 ± 5.99%* respectively; HDFa was 84.58 ± 10.41%, 19.54 ± 3.06%**, and 96.28 ± 33.67%, respectively, in the extraction assay. In the cell insert model, cell viability of L929 cells were 95.25 ± 0.96%, 47.49 ± 5.37%**, and 48.63 ± 7.00%**, respectively; HDFa cell viability were 92.80 ± 1.29%, 38.86 ± 4.28%**, and 49.90 ± 2.55%** (*: P < .01; **P < .001 compared with CSG-PHMB; cell viability of culture medium without treatment at day 1 was 100%). The cell extraction model on day 1 indicated that CSG-PHMB had higher viability of L929 cells compared with BXG. In addition, the cellular viability results indicated that CSG-PHMB gel exhibited lower cytotoxicity when compared with BXG and PXG in the cell insert model assay. Within the in vitro debridement model, CSG-PHMB exhibited an ability to potentially increase the loosening of the collagen matrix. The reason for this may be because of the concentrated surfactant found within the CSG-PHMB, which has the ability to lower the surface tension, aiding in the movements of fragments and debris in the fluorescent artificial wound eschar model (fAWE).

Mono- to Multilayer Transition in Growing Bacterial Colonies

The transition from monolayers to multilayered structures in bacterial colonies is a fundamental step in biofilm development. Observed across different morphotypes and species, this transition is triggered within freely growing bacterial microcolonies comprising a few hundred cells. Using a combination of numerical simulations and analytical modeling, here we demonstrate that this transition originates from the competition between growth-induced in-plane active stresses and vertical restoring forces, due to the cell-substrate interactions. Using a simple chainlike colony of laterally confined cells, we show that the transition sets when individual cells become unstable to rotations; thus it is localized and mechanically deterministic. Asynchronous cell division renders the process stochastic, so that all the critical parameters that control the onset of the transition are continuously distributed random variables. Here we demonstrate that the occurrence of the first division in the colony can be approximated as a Poisson process in the limit of large cell numbers. This allows us to approximately calculate the probability distribution function of the position and time associated with the first extrusion. The rate of such a Poisson process can be identified as the order parameter of the transition, thus highlighting its mixed deterministic-stochastic nature.

Deep-Subsurface Pressure Stimulates Metabolic Plasticity in Shale-Colonizing Halanaerobium spp

Bacterial Halanaerobium strains become the dominant persisting microbial community member in produced fluids across geographically distinct hydraulically fractured shales. Halanaerobium is believed to be inadvertently introduced into this environment during the drilling and fracturing process and must therefore tolerate large changes in pressure, temperature, and salinity. Here, we used a Halanaerobium strain isolated from a natural gas well in the Utica Point Pleasant formation to investigate metabolic and physiological responses to growth under high-pressure subsurface conditions. Laboratory incubations confirmed the ability of Halanaerobium congolense strain WG8 to grow under pressures representative of deep shale formations (21 to 48 MPa). Under these conditions, broad metabolic and physiological shifts were identified, including higher abundances of proteins associated with the production of extracellular polymeric substances. Confocal laser scanning microscopy indicated that extracellular polymeric substance (EPS) production was associated with greater cell aggregation when biomass was cultured at high pressure. Changes in Halanaerobium central carbon metabolism under the same conditions were inferred from nuclear magnetic resonance (NMR) and gas chromatography measurements, revealing large per-cell increases in production of ethanol, acetate, and propanol and cessation of hydrogen production. These metabolic shifts were associated with carbon flux through 1,2-propanediol in response to slower fluxes of carbon through stage 3 of glycolysis. Together, these results reveal the potential for bioclogging and corrosion (via organic acid fermentation products) associated with persistent Halanaerobium growth in deep, hydraulically fractured shale ecosystems, and offer new insights into cellular mechanisms that enable these strains to dominate deep-shale microbiomes.IMPORTANCE The hydraulic fracturing of deep-shale formations for hydrocarbon recovery accounts for approximately 60% of U.S. natural gas production. Microbial activity associated with this process is generally considered deleterious due to issues associated with sulfide production, microbially induced corrosion, and bioclogging in the subsurface. Here we demonstrate that a representative Halanaerobium species, frequently the dominant microbial taxon in hydraulically fractured shales, responds to pressures characteristic of the deep subsurface by shifting its metabolism to generate more corrosive organic acids and produce more polymeric substances that cause "clumping" of biomass. While the potential for increased corrosion of steel infrastructure and clogging of pores and fractures in the subsurface may significantly impact hydrocarbon recovery, these data also offer new insights for microbial control in these ecosystems.

Biomechanical Feedback Strengthens Jammed Cellular Packings

Growth in confined spaces can drive cellular populations through a jamming transition from a fluidlike state to a solidlike state. Experiments have found that jammed budding yeast populations can build up extreme compressive pressures (over 1 MPa), which in turn feed back onto cellular physiology by slowing or even stalling cell growth. Using numerical simulations, we investigate how this feedback impacts the mechanical properties of model jammed cell populations. We find that feedback directs growth toward poorly coordinated regions, resulting in an excess number of cell-cell contacts that rigidify cell packings. Cell packings possess anomalously large shear and bulk moduli that depend sensitively on the strength of feedback. These results demonstrate that mechanical feedback on the single-cell level is a simple mechanism by which living systems may tune their population-level mechanical properties.

Active Modulation of States of Prestress in Self-Assembled Short Peptide Gels

Peptide hydrogels are excellent candidates for medical therapeutics due to their tuneable viscoelastic properties, however, in vivo they will be subject to various osmotic pressures, temperature changes, and biological co-solutes, which could alter their performance. Peptide hydrogels formed from the synthetic peptide I3K have a temperature-induced hardening of their shear modulus by a factor of 2. We show that the addition of uncross-linked poly( N-isopropylacrylamide) chains to the peptide gels increases the gels' temperature sensitivity by 3 orders of magnitude through the control of osmotic swelling and cross-linking. Using machine learning combined with single-molecule fluorescence microscopy, we measured the modulation of states of prestress in the gels on the level of single peptide fibers. A new self-consistent mixture model was developed to simultaneously quantify the energy and the length distributions of the states of prestress. Switching the temperature from 20 to 40 °C causes 6-fold increases in the number of states of prestress. At the higher temperature, many of the fibers experience constrained buckling with characteristic small wavelength oscillations in their curvature.