REPOSITORY > RESULTS

Abstract

Naturally formed microbial communities are present in the form of cellular aggregates that create a set of diverse biochemical pathways through cross-feeding between the members of the microbial community. One of the most important factors so that some biochemical reactions can occur is the appropriate spatial placement of a particular bacterium with its metabolic capability, which results in the formation of closed biogeochemical cycles that increase metabolic efficiency and robustness of the community. Even though many bacteria have a set of optimized metabolic traits, the absence of the initial conditions, which promote the attachment of compatible bacteria, prevents them from forming closed biochemical cycles. If we provide the conditions to first, couple the cells together, and second, make them compatible, we can assemble different bacteria in flocs, similarly as it occurs in nature. Since bacteria are charged, it allows us to alter their cell charge using electrostatic deposition of oppositely charged polyelectrolyte (PE). As a result, oppositely charged bacterial cells can be attached to each other or to the surface of a material merely by electrostatic interaction. Therefore, to be able to simulate the naturally aggregated cellular structures, we aimed to develop a method to modify the bacterial cell surface using the strategy of PE deposition. We used it to study the biological responses caused by the changes in the properties of the cell surface and the physical confinement of cells. Knowledge of biological responses can be further used to our advantage. The construction of artificial aggregated structures allows us to carry out specific biogeochemical cycles in applicative setups for bioremediation, biotechnology or biomedicine.
The main goal in our study was to prepare the approach for the deposition of tailor-made PE coatings on the surface of a bacterial cell, which altered the cell surface charge, controlling the time of the first cellular division and the formation of cell aggregation. The thickness of the coating determined the delay of cell division and the increase in cell size and the production of Green Fluorescent Protein (GFP) up to 2 and 5 times, respectively. In some cases, the introduction of the PE coating led to a decrease in cell viability, therefore, we selected two strains, based on their resistance to the PEs, to assess the effect of PEs on cell viability and to find the conditions that would not reduce it. The toxicity of PEs was found to be dependent firstly, on the strain, and secondly, on the conditions of exposure to the PEs, which was manifested by different outcomes in viability. In order to improve cell viability, we used two approaches: (i) using a decreased PE concentration and (ii) using acetylation to reduce the positive PE, which both enabled us to safely use the PEs for various bacterial strains. We also extended the applicative potential of our method by combining it with graphene and paramagnetic nanoparticles (NPs).
In conclusion, we prepared a versatile method for the preparation of artificial aggregates based on the electrostatic method, which allows us to study the physiology of bacterial cells and to produce artificial cellular structures with potential for biotechnological, biomedical and environmental solutions.