Single-cell yolk-shell capsules with high biological activity and stability

(Nanowerk News) The value of the global market for microbes and microbial products is continuously increasing. However, the full exploitation of bacteria towards advanced biotechnology and bio-energetics is impeded by low biological activity and stability in the industrial reactors.
Single-cell nanoencapsulation is an emerging, non-genetic technique to address these limitations. It concerns to create extended cell surface functionalities, provide external stimuli to enhance cell stability and activity, and incorporate new properties.
Colloidal packing is a common strategy for single-cell nanoencapsulation through an adsorption-assembly-encapsulation sequence. However, the disordered structure of current generation colloidal packings does not allow well-controlled exchange between a cell and its environment, affecting nutrient, waste and metabolite diffusion and therefore, cell activity and stability.
Moreover, such colloidal packing results in direct contact between the shell and the cell surface, which is incompatible with cells and negatively affects their activity and stability even further.
In response to this challenge, inspired by the yolk-shell structure of eggs and the structural ordering of cell surfaces in the evolution, the living materials team led by Prof. Bao-Lian Su from Wuhan University of Technology and the University of Namur proposed highly stable single cyanobacterium capsules with an ordered yolk-shell structure of uniformly organized and tunable nanoporosity shaped by protein-assisted, hydrophilic colloidal silica packing (National Science Review, "Single-cell yolk-shell nanoencapsulation for long-term viability with size-dependent permeability and molecular recognition").
chematic illustration of sequential steps for yolk-shell encapsulation of cyanobacterium
(a) Schematic illustration of sequential steps for yolk-shell encapsulation of cyanobacterium. (b) SEM micrograph of the encapsulated cyanobacteria with the corresponding EDX mapping for elemental Si and O. Scale bars: 2 µm. (c) Merged CLSM micrograph of encapsulated cyanobacteria, showing encapsulated, red-fluorescent cyanobacteria and green-fluorescent silica shells. Scale bar: 5 µm. (d) TEM micrograph of an encapsulated cyanobacterium, showing intracellular structures and the colloidal packing layer. Scale bar: 500 nm. (e) HAADF-STEM micrograph and FFT (inset) image of an encapsulated cyanobacterium. The FFT image indicates ordered of the colloidal packing. Scale bar: 500 nm. (© Science China Press) (click on image to enlarge)
The void between the ordered nanoporous shell and cell is created by the controlled internalization of protamine, which could subsequently be filled by nutrients. Shells thus constructed are not only biocompatible but also endow introduction of new and unprecedented cell surface functionalities, such as specific size-dependent permeability and defined molecular recognition abilities.
Owing to the presence of the buffering interstitial hollow space filled by nutrient between the ordered nanoporous shell and the cell surface, cyanobacterial activity, and stability evolving from this yolk-shell encapsulation technology are highly enhanced.
Because of the specific size-dependent permeability stemming from uniformly organized nanoporosity, the survival ability of yolk-shell encapsulated cyanobacteria against toxic chemical environments is significantly strengthened. In addition, this yolk-shell structure can also be equipped with molecular recognition abilities.
It is envisioned single cells encapsulated in their ordered yolk-shell structures have a broad scope in a wide range of applications with specific functionalities, including in photobioreactors, biochips, biosensors, biocatalysis, biofuel reactors, and controlled delivery therapeutics.
Source: Science China Press
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