Cytoplasm of Saccharomyces cerevisiae yeast cells contains a significant amount of desired intracellular products for both industrial utility and academic research. To recover intracellular compounds, it is necessary to break the yeast cells with high efficiency, which, under certain circumstances, requires the use of the lytic enzyme zymolyase to completely digest the cell walls. A promising strategy for zymolyase immobilization on silk fibroin (SF) was developed. SF/Fe3O4 magnetic microspheres (MMs) were constructed by solvent (ethanol)-induced self-assembly of SF surrounding Fe3O4 magnetic nanoparticles (MNs), which were synthesized by a coprecipitation method. Zymolyase was covalently bonded on the surface of the SF/Fe3O4 MMs by a photochemical cross-linking method to produce robust biocatalysts of zymolyase/SF/Fe3O4. The chemical, magnetic, and morphological properties of the MM supports and the immobilized zymolyase were investigated. Enzymolysis results demonstrated that the immobilized zymolyase showed good activity and stability for digesting yeast cell walls, and the biocatalyst can be readily recycled through convenient magnetic separation for reuse. At the optimum pH = 7.5, the immobilized zymolyase maintained 84% of the activity of the free zymolyase and retained 41% of its initial activity after four times of reuse. At unfavorable acidic pH = 4, the immobilized zymolyase retained 81% of its initial activity, while the free zymolyase showed no significant activity. Consequently, the SF/Fe3O4 MMs exhibit superior performance in terms of immobilizing enzymes, which have a good prospect in the biological application.

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Macroscopic supramolecular assembly (MSA) is a new concept of supramolecular science with an emphasis on noncovalent interactions between macroscopic building blocks with sizes exceeding 10 μm. Owing to a similar noncovalently interactive nature with the phenomena of bioadhesion, self-healing, etc. and flexible features in tailoring and designing modular building blocks, MSA has been developed as a simplified model to interpret interfacial phenomena and a facile method to fabricate supramolecular materials. However, at this early stage, MSA has always been limited to hydrogel materials, which provide flowability for high molecular mobility to the interfacial binding. The extension to a wide range of materials for MSA is desired. Herein, we have developed a strategy of adjusting intrinsic properties (e.g., elastic modulus) of nonhydrogel materials to realize MSA, which could broaden the material choices of MSA. Using the widely used elastomer of poly­(dimethylsiloxane) (PDMS) as building blocks, we have demonstrated the elastic-modulus-dependent MSA of PDMS based on the host/guest molecular recognition between supramolecular groups of β-cyclodextrin and adamantane. In the varied elastic modulus range of 0.38 to 3.84 MPa, we obtained the trend of the MSA probability decreasing from 100% at 0.38 MPa to 0% at 3.84 MPa. Meanwhile, in situ measurements of interactive forces between PDMS building blocks have supported the observed assembly phenomena. The underlying reasons are interpreted with the low-modulus flexible surfaces favoring for high molecular mobility to achieve interactions between multiple sites at the interface based on the theory of multivalency. Taken together, we have demonstrated the feasibility of directly adjusting the modulus of bulk materials to realize MSA of nonhydrogel materials, which may provide clues to the fast wet adhesion and new solutions to the additive manufacture of elastomer materials.

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Preparation of protoplasts of Saccharomyces cerevisiae and Pichia pastoris was achieved by using iron oxide (Fe 3 O 4 ) magnetic nanoparticles (MNPs). The protoplasts were characterized by optical microscopy, atomic force microscopy, scanning electron microscopy, and energy-dispersive spectroscopy, revealing cell wall breakage. In addition, the as-prepared protoplasts allowed regeneration, DNA extraction, and transformation. These results support the conviction that Fe 3 O 4 MNPs exhibit an intrinsic yeast lytic activity. The demonstration of protoplast generation can be useful in providing a feasible platform for genetic manipulation of yeasts and opens doors for yeast-based biotechnological applications. Moreover, it is anticipated that, with appropriate modifications, this approach can be extended to a range of microbiomes of industrial importance.