Optimizing Silica Encapsulation of Living Cells: In Situ Evaluation of Cellular Stress

Abstract

The encapsulation of living cells in materials with good optical and mechanical properties often produces death or stress due to the release of toxic byproducts originated during the synthesis. We present here a method to assess the cellular stress that silica entrapment exerts over living cells taking into account the main preparation variables such as the nature of the silica source, protecting functional groups, total solid concentration, or indirect procedures. Measurement of the cellular stress status of genetically modified Sacharomyces cereVisiae, a true biological probe, allowed us to perform a quantitative analysis of cellular stress in a short time basis (compared to conventional long-term viability tests), opening the gate for a more sophisticated approach to optimize the synthesis conditions. In addition, the aforementioned findings allowed the preparation of novel materials with enhanced optical and mechanical properties. The relation of cellular stress with initial viability is also discussed.

Bioluminescence of Pseudomonas fluorescens HK44 in the course of encapsulation into silica gel. Effect of methanol

“…Our results shed some light on this contradiction: the principal negative effect of MeOH on encapsulated cells was confirmed; nevertheless, in comparison with free cells, Si(OMe) 4 -encapsulated cells were more stressed by the same amount of MeOH. Other encapsulation stresses, which are not eliminated using non-alcoholic routes, include osmotic stress (Perullini et al 2008), heat stress (Premkumar et al 2001) as well as matrix shrinkage and cell compression during aging (Brinker and Scherer 1990;Gill and Ballesteros 2000;Raff et al 2003). The abatement of these stresses frequently results in a worsening of the transparency and mechanical properties of silica biogels .…”

“…The monitoring of immobilization stress is a complicated task; the best results have been obtained using engineered microorganisms selectively responding to particular stress causes by BLM or fluorescence (Premkumar et al 2001(Premkumar et al , 2002aSagi et al 2003;Perullini et al 2008). Changes in light emission or the production of fluorescent compounds by microorganisms might also be used as signals of unspecified stress (Kuncová et al 2004;Tessema et al 2006).…”

Encapsulation of cells within silica matrixes: Towards a new advance in the conception of living hybrid materials

“…Recently, Bilmes et al demonstrate the importance of the preparation pathway on the cellular stress encounter by the encapsulated yeast cells. Using a non-invasive method (reporter gene), they show that the nature of the silica source, the synthesis procedure and the addition of additives modulate the cellular stress and thus the cell viability [48]. These hybrid materials, synthesized in the right conditions, can improve the overall hazardous metal uptake [49] and allow the design of continuous bioreactor able to degrade toxic compounds (e.g.…”

Prolonging the lifetime and activity of silica immobilised Cyanidium caldarium

“…Further to this a method to drastically reduce the amount of Na + , an ion that interferes with the natural osmoregulation of a cell, has been developed [8]. In this method Ludox, used widely in aqueous based silica immobilisations [9,[21][22][23], was replaced by a silica nanopowder that tended to aggregate upon sonication with the silica sol. These aggregates would therefore play the role of a strengthening additive analogous with Ludox, yet they were too large to be internalised within a living cell unlike Ludox colloids.…”