RESUMEN
Cross-linking, also called tanning, improves mechanical properties of leather and also increases its enzymatic and thermal stability. As a final product, leather has an ultimate tensile strength (σ) of 8-25 MPa and an elongation at break (ε) of >30 %. Mycelium-based materials are a sustainable alternative to leather. Here, the effect of cross-linkers was assessed on mechanical properties of Schizophyllum commune mycelium sheets. To this end, glutaraldehyde and N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) were used as well as extracts of Ligustrum vulgare leaves, and bark of Acacia mearnsii and Caesalpinia spinosa. Untanned sheets had a σ of 7.8 MPa and an ε of 15.2 %, while the best overall combination of strength and elasticity was obtained with 0.1 % glutaraldehyde with a σ of 11.1 MPa and an ε of 14.6 %. Cross-linking also increased enzymatic stability and reduced mycelial water absorption but did not result in increased thermal stability. Fourier transform infrared spectroscopy (FTIR), 1D nuclear magnetic resonance spectroscopy (NMR), and amino acid analysis showed that glutaraldehyde bound both protein amino groups and polysaccharide hydroxyl groups by forming Schiff bases and acetals, respectively. Together, synthetic and vegetable cross-linkers can be used to obtain mycelium materials with leather-like tensile strength.
RESUMEN
The cell wall fulfils several functions in the biology of fungi. For instance, it provides mechanical strength, interacts with the (a)biotic environment, and acts as a molecular sieve. Recently, it was shown that proteins and ß-glucans in the cell wall of Schizophyllum commune bind Cu2+. We here show that the cell wall of this mushroom forming fungus also binds other (micro-)nutrients. Ca2+, Mg2+, Mn2+, NO3-, PO43-, and SO42- bound at levels > 1 mg per gram dry weight cell wall, while binding of BO3-, Cu2+, Zn2+ and MoO42- was lower. Sorption of Ca2+, Mn2+, Zn2+ and PO43- was promoted at alkaline pH. These compounds as well as BO33-, Cu2+, Mg2+, NO3-, and SO42- that had bound at pH 4, 6, or 8 could be released from the cell wall at pH 4 with a maximum efficiency of 46-93 %. Solid-state NMR spectroscopy showed that the metals had the same binding sites as Cu2+ when a low concentration of this ion is used. Moreover, data indicate that anions bind to the cell wall as well as to the metal ions. Together, it is shown that the cell wall of S. commune binds various (micro-)nutrients and that this binding is higher than the uptake by hyphae. The binding to the cell wall may be used as a storage mechanism or may reduce availability of these molecules to competitors or prevent toxic influx in the cytoplasm.
RESUMEN
The current rise of antibiotic resistant forms of Mycobacterium tuberculosis is a global health threat that calls for new antibiotics. The ß-lactamase BlaC of this pathogen prevents the use of ß-lactam antibiotics, except in combination with a ß-lactamase inhibitor. To understand if exposure to such inhibitors can easily result in resistance, a BlaC evolution experiment was performed, studying the evolutionary adaptability against the inhibitor sulbactam. Several amino acid substitutions in BlaC were shown to confer reduced sensitivity to sulbactam. The G132S mutation causes a reduction in the rate of nitrocefin and ampicillin hydrolysis and simultaneously reduces the sensitivity for sulbactam inhibition. Introduction of the side chain moiety of Ser132 causes the 104-105 peptide bond to assume the cis conformation and the side chain of Ser104 to be rotated toward the sulbactam adduct with which it forms a hydrogen bond not present in the wild-type enzyme. The gatekeeper residue Ile105 also moves. These changes in the entrance of the active site can explain the decreased affinity of G132S BlaC for both substrates and sulbactam. Our results show that BlaC can easily acquire a reduced sensitivity for sulbactam, with a single-amino acid mutation, which could hinder the use of combination therapies.