Research

Electrostatic immobilisation of bacterial cells and effects on their physiology

Code:

J4-7640

Range:

01. March 2016 - 28. February 2019

Range:

0,04 FTE

Leader:

Julijana Kristl

Field:

4.06.04 Biotechnical sciences/Biotechnology/Microbe biotechnology

Abstract:

In nature, the extracellular matrix, which encloses bacterial cells, has a vital role for normal cell functioning. Such confinement serves as protection against predators and antimicrobial agents, allows the establishment of high cell densities and co-aggregation of different types of cells and provides a matrix, where different bioactive molecules can concentrate. In biotechnological processes these natural principles can by exploited by artificially implementing immobilization of bacterial cells. It has been shown in several cases that this approach can be extremely potent, due to procedure simplification and increased efficiency of the biotechnological processes. However, currently established methods of cell immobilization are generally based on aggregation of bacterial cells by dehydration and consecutive pelletisation, by entrapment in gel or sol-gel based matrix or within a cross-linked natural (e.g. alginate, carrageenan) or artificial polymer (e.g. polyacrylamide, polyethylene glycol, polyvinyl alcohols) based matrix. Since the matrix-cell interaction is based on physicochemical principles, the knowledge of colloid physics can be extremely important for the development of new immobilization strategies. One such new strategy can be based on the adaptation of deposition of charged polymers used in layer-by-layer (LBL) methods. This method has been extensively investigated and fully exploited for surface modifications of inorganic and organic nonliving materials, either on two dimensional (surfaces of different materials) or on three dimensional surfaces (micro-, nano-particles). Capsules that are formed this way, are very thin, as well as porous, but at the same time have tremendous elastic and strength properties, since polymers are deposited on a surface in thin tailor made shell, where each layer is directly deposited on charged surface forming a mesh of a few nm thickness. By utilizing different LBL encapsulation strategies through variation of ionic strength, pH, different types and sizes of polymers and levels of branching, as well as induction of hydrogen and covalent bonds between polymers, the properties, such as porosity, capsule thickness and strength as well as surface charge, can be controlled. Since bacterial cells can be treated as a special case of soft matter, with the membrane and cell wall surface forming a negatively charged surface, we can exploit this intrinsic property for encapsulation, surface modification, entrapment and immobilization, by using polyelectrolyte polymers in a similar way as deposition of polyelectrolytes on non-living surfaces or particles using modified conventional LBL method. Accordingly, our hypothesis is that it is possible to permanently and efficiently entrap bacterial cells within layers of polyelectrolytes. Contrary to past studies, we are taking into account that micron sized bacterial cells are different than non-living micro-particles normally used in LBL encapsulation, since these cells: (i) have very diverse surface softness due to production of extracellular matrix of different texture, as well as dynamic wall architecture, (ii) can adapt metabolically or by cell surface organization after the deposition of charged colloids on cell surface, (iii) positively charged polycations can affect viability of bacterial cells and most notably (iv) LBL coating of cells affects cell physiology due to capsule porosity, diffusion of nutrients and by physical mitigation of cell mass gaining and division. Based on this hypothesis the aims in this project are to: (i) develop an LBL immobilization strategy for bacterial cells, (ii) characterize physicochemically and microscopically such LBL immobilized bacteria, (iii) determine the effect of polyelectrolyte encapsulation on physiology and cell division and (iv) to evaluate the changes of mass balances of LBL immobilized cells in comparison to free-living cells.