The effects of low levels of trivalent ions on a standard strain of Escherichia coli (ATCC 11775) in aqueous solutions

Influence of Metal Cations on the Viscoelastic Properties of Escherichia coli Biofilms

Biofilms frequently cause complications in various areas of human life, e.g., in medicine and in the food industry. More recently, biofilms are discussed as new types of living materials with tunable mechanical properties. In particular, Escherichia coli produces a matrix composed of amyloid-forming curli and phosphoethanolamine-modified cellulose fibers in response to suboptimal environmental conditions. It is currently unknown how the interaction between these fibers contributes to the overall mechanical properties of the formed biofilms and if extrinsic control parameters can be utilized to manipulate these properties. Using shear rheology, we show that biofilms formed by the E. coli K-12 strain AR3110 stiffen by a factor of 2 when exposed to the trivalent metal cations Al(III) and Fe(III), while no such response is observed for the bivalent cations Zn(II) and Ca(II). Strains producing only one matrix component did not show any stiffening response to either cation or even a small softening. No stiffening response was further observed when strains producing only one type of fiber were co-cultured or simply mixed after biofilm growth. These results suggest that the E. coli biofilm matrix is a uniquely structured composite material when both matrix fibers are produced from the same bacterium. While the exact interaction mechanism between curli, phosphoethanolamine-modified cellulose, and trivalent metal cations is currently not known, our results highlight the potential of using extrinsic parameters to understand and control the interplay between biofilm structure and mechanical properties. This will ultimately aid in the development of better strategies for controlling biofilm growth.

Removal of hazardous ions from aqueous solutions: Current methods, with a focus on green ion flotation

Hazardous ions, like those of heavy metals, cause significant health and environmental problems when they are discharged into water resources naturally or through various industrial processes. Removing these ions from water is of significant importance in the provision of high-quality water for drinking and agricultural usage. This work discusses current techniques that are frequently used for the removal of heavy-metal ions from aqueous solutions by absorption, particularly the use of biodegradable surfactants in ion flotation. Certain new surfactants promise high efficiency in their use in the ion-flotation process and in their application in industrial-water treatment to remove heavy metals. As an example, this work demonstrates the high efficiency of surfactants based on an amino-acid (L-cysteine) in removing a range of heavy-metal ions in a simple, single-stage ion-flotation process. High foaming ability, the ability to operate in various temperatures and pHs, decomposing into natural products and high binding affinity for heavy-metal ions make the cysteine-based surfactants a highly suitable compound to replace current commercial surfactants in ion- and froth-flotation processes. Removal of particular ions can also be achieved in ion flotation; a suitable choice of parameters, such as pH and surfactant concentration, favours the surfactant binding to those ions. Further intensive work is required to develop an optimal process to recover valuable elements from waste solutions.

A high-conductive, anti-freezing, antibacterial and anti-swelling starch-based physical hydrogel for multifunctional flexible wearable sensors

Flexible wearable sensors based on conductive hydrogels are attracting increasing interest. To meet the urgent demands of sustainability and eco-friendliness, biopolymer-based physically crosslinked hydrogels have drawn great attention. Starch has a great potential due to its renewability, biocompatibility, nontoxicity and low cost. However, poor mechanical property, low conductivity and lack of versatility are seriously limiting the applications of starch-based hydrogels in wearable sensors. Moreover, the development of starch hydrogel-based wearable sensors in harsh conditions remains a challenge. Herein, multifunctional and physical crosslinking hydrogels were developed by introducing ionic liquid (1-ethyl-3-methyl imidazolium acetate) and metal salt (AlCl₃) into starch/polyvinyl alcohol double-network structure. The hydrogel exhibited excellent stretchability (567%), tensile strength (0.53 MPa), high conductivity (2.75 S·m^-1), good anti-freezing, antibacterial and anti-swelling properties. A wearable sensor assembled from the starch-based hydrogel exhibited a wide working range, high sensitivity (gauge factor: 5.93) and excellent reversibility. Due to the versatility, the sensor effectively detected human motion in normal and underwater environment, and possessed a sensitive pressure and thermal response. Overall, the present work provided a promising route to develop multifunctional and "green" biopolymer-based hydrogels for wearable sensors in human health and sporting applications.

Magnetic porous NiLa-Layered double oxides (LDOs) with improved phosphate adsorption and antibacterial activity for treatment of secondary effluent

The removal of phosphate (nutrient) and E. coli (pathogen) from secondary effluent is of great importance to control the water quality of the receiving water bodies. In this study, magnetic porous NiLa-layered double oxides (NiLa-LDOs/Fe₃O₄) were synthesized using a simple co-precipitation method. NiLa-LDOs/Fe₃O₄ exhibited a high phosphate adsorption capacity of 203.10 mg g^-1 in batch adsorption experiments, which can mostly be maintained within the pH range (5.5-8.5) and ionic strength range (5-20 mM) of secondary effluent, and in the presence of commonly co-existing species (anions and organics). NiLa-LDOs/Fe₃O₄ were further evaluated in real secondary effluent and the homogenous surface diffusion model (HSDM) was used to predict the performance in field applications. Under typical conditions, NiLa-LDOs/Fe₃O₄ can last for ∼1845-2448 bed volumes (BVs) before the phosphate concentration in the effluent exceeds the monthly average limit of 1 mg L^-1 P. Good regeneration capacities were also demonstrated in cyclic adsorption-desorption runs in both synthetic solution and secondary effluent. In addition, the presence of Ni and La species greatly enhanced the antibacterial performance of the NiLa-LDOs/Fe₃O₄ toward E. coli. Results obtained from this study indicate porous NiLa-LDOs/Fe₃O₄ can be a promising multifunctional material for the treatment of secondary effluent.

The effects of low levels of trivalent ions on a standard strain of Escherichia coli (ATCC 11775) in aqueous solutions

Considering the ever‐growing usage of trivalent salts in water treatment, for example, lanthanum salts in rare earth, AlCl₃ and FeCl₃, the effects of different trivalent cations on the bacterium Escherichia coli (E. coli) ATCC 11775 strain have been studied in aqueous solutions. From colony incubation studies, the colony‐forming unit (CFU) densities were found to decrease significantly in the presence of even low levels (10⁻⁵ mol/L) of lanthanum chloride. This level of reduction in CFU number is comparable to the results obtained using the known bacteriocidal cationic surfactant, C₁₄TAB. By comparison, exposure of the cells to low levels of trivalent ion, aluminum and chromium ion solutions produced only modest reductions in CFU density. The results from the incubation studies suggest that the bacteriostatic mechanism of La³⁺ ions has similarities to that of the cationic surfactant, and different to that of the other trivalent ions. Size distribution and zeta potential measurements of E. coli cells and phospholipid vesicles in the presence of trivalent cations solutions suggested significant cell shrinkage probably caused by membrane disruption.