Progress in emerging techniques for characterization of immobilized viable whole-cell biocatalysts

Immobilized Cell Physiology Imaging and Stabilization of Enzyme Cascade Reaction Using Recombinant Cells Escherichia coli Entrapped in Polyelectrolyte Complex Beads by Jet Break-Up Encapsulator

A novel, high performance, and scalable immobilization protocol using a laminar jet break-up technique was developed for the production of polyelectrolyte complex beads with entrapped viable Escherichia coli cells expressing an enzyme cascade of alcohol dehydrogenase, enoate reductase, and cyclohexanone monooxygenase. A significant improvement of operational stability was achieved by cell immobilization, which was manifested as an almost two-fold higher summative product yield of 63% after five cascade reaction cycles as compared to the yield using free cells of 36% after the maximum achievable number of three cycles. Correspondingly, increased metabolic activity was observed by multimodal optical imaging in entrapped cells, which was in contrast to a complete suppression of cell metabolism in free cells after five reaction cycles. Additionally, a high density of cells entrapped in beads had a negligible effect on bead permeability for low molecular weight substrates and products of cascade reaction.

Simulation-based optimisation of thermodynamic conditions in the ESEM for dynamical in-situ study of spherical polyelectrolyte complex particles in their native state

We present a complex analysis and optimisation of dynamic conditions in the environmental scanning electron microscope (ESEM) to allow in-situ observation of extremely delicate wet bio-polymeric spherical particles in their native state. According to the results of gas flow and heat transfer simulations, we were able to develop an improved procedure leading to thermodynamic equilibrium between the sample and chamber environment. To quantify and hence minimise the extent of any sample deformation during specimen chamber pumping, a strength-stress analysis is used. Monte Carlo simulations of beam-gas, -water, and -sample interactions describe beam scattering, absorbed energy, interaction volume and the emission of signal electrons in the ESEM. Finally, we discuss sample damage as a result of drying and the production of beam-induced free radicals. Based on all experimental and simulation results we introduce a Delicate Sample Observation Strategy for the ESEM. We show how this strategy can be applied to the characterization of polyelectrolyte complex spherical particles containing immobilized recombinant cells E. coli overexpressing cyclohexanone monooxygenase, used as a model biocatalyst. We present the first native-state electron microscopy images of the viscous core of a halved polyelectrolyte complex capsule containing living cells.