Microbial biofilms: New catalysts for maximizing productivity of long-term biotransformations

Abstract

The performance of biocatalytic reactions is often hampered by product and/or substrate toxicity and short-term reaction times due to instable biocatalysts. Microbes in biofilms show a remarkable resistance against biocides and form stable communities. In nature, especially in environments characterized by harsh conditions such as heavily contaminated sites, cells grow pre-dominantly in biofilms, which enable them to cope with physiological stress. This robustness was utilized to design a bioprocess concept based on catalytic biofilms for stable long-term transformations of toxic reactants. Sixty-nine bacterial strains have been screened to find organisms suitable for biofilm-based biotransformations. This included host strains important for recombinant enzyme expression and strains isolated from biofilters or contaminated soils. Nearly all organisms with bioremediation potential showed good biofilm forming capacities. Pseudomonas sp. strain VLB120DeltaC was chosen as a model organism due to its excellent biofilm forming capacity and its well-studied capability of catalyzing asymmetric epoxidations. A tubular reactor was used for the biotransformation of styrene to (S)-styrene oxide as a model reaction. The process was stable for at least 55 days at a maximal volumetric productivity of 16 g/(L(aq) day) and a yield of 9 mol%. In situ product extraction prevented product inhibition of the catalyst. Biofilm physiology and dynamics are characterized during the biotransformation and limitations and advantages of this reaction concept are discussed.

Characterization of a biofilm membrane reactor and its prospects for fine chemical synthesis

“…The partition coefficient of styrene oxide ( P) in a twophase mixture of styrene and M9 minimal medium was determined to be (240 AE 20) (Gross et al, 2007). Before the measurements started, the medium bottle was supplied with 20 mM styrene oxide (maximal solubility) and the system has been equilibrated for 12-16 h at the flow rate set for the experiment.…”

“…The biomass grown inside the tubes was determined as biomass dry weight (bdw) at the end of cultivation according to (Gross et al, 2007).…”

“…Current research with biofilms has begun to focus on the production of high-priced chemicals (Gross et al, 2007;Li et al, 2006;Setyawati et al, 2009).…”

“…> 99%) by the engineered Pseudomonas sp. strain VLB120DC (Gross et al, 2007). A micro plug flow reactor was designed based on a single silicone tube where the biofilm grew attached on the inner side of the tube.…”

“…By utilizing the substrate styrene concurrently as a second organic phase, the product (S)-styrene oxide could be extracted from the aqueous phase, facilitating downstream processing and preventing product toxicity (Gross et al, 2007).…”