Statistical vs. stochastic experimental design: an experimental comparison on the example of protein refolding.

Optimization of experimental problems is a challenging task in both engineering and science. In principle, two different design of experiments (DOE) strategies exist: statistical and stochastic methods. Both aim to efficiently and precisely identify optimal solutions inside the problem-specific search space.

Novel whole-cell biocatalysts with recombinant hydroxysteroid dehydrogenases for the asymmetric reduction of dehydrocholic acid.

Ursodeoxycholic acid is an important pharmaceutical so far chemically synthesized from cholic acid. Various biocatalytic alternatives have already been discussed with hydroxysteroid dehydrogenases (HSDH) playing a crucial role. Several whole-cell biocatalysts based on a 7α-HSDH-knockout strain of Escherichia coli overexpressing a recently identified 7β-HSDH from Collinsella aerofaciens and a NAD(P)-bispecific formate dehydrogenase mutant from Mycobacterium vaccae for internal cofactor regeneration were designed and characterized.

Experimental optimization of protein refolding with a genetic algorithm.

Refolding of proteins from solubilized inclusion bodies still represents a major challenge for many recombinantly expressed proteins and often constitutes a major bottleneck. As in vitro refolding is a complex reaction with a variety of critical parameters, suitable refolding conditions are typically derived empirically in extensive screening experiments. Here, we introduce a new strategy that combines screening and optimization of refolding yields with a genetic algorithm (GA).

Rapid media transition: an experimental approach for steady state analysis of metabolic pathways.

Commonly steady state analysis of microbial metabolism is performed under well defined physiological conditions in continuous cultures with fixed external rates. However, most industrial bioprocesses are operated in fed-batch mode under non-stationary conditions, which cannot be realized in chemostat cultures. A novel experimental setup-rapid media transition-enables steady state perturbation of metabolism on a time scale of several minutes in parallel to operating bioprocesses.