Michael Schlömann

Two phenylacetaldehyde dehydrogenases, originating from Escherichia coli K-12 (FeaB-K-12) and Sphingopyxis fribergensis Kp5.2 (FeaB-Kp5.2), were immobilized on powdery silica carrier with various functionalization. First, the suitability of these carriers for application in combination with phenylacetaldehydes and phenylacetic acids was studied. Out of two carriers functionalized differently, mesoporous cellular foam, whose surface was modified with 3-glycidyloxypropyl groups (MCF-G), showed promising results. Hence, this carrier was further tested at 17 different immobilization conditions. Despite both enzymes showing high immobilization efficiency, the initial activities were relatively low compared to the free enzymes. Interestingly, the immobilized FeaB-Kp5.2 on MCF-G-Kw showed about 80% of retained activity after two months of incubation at 0 °C, indicating that the immobilization enhances the stability of this enzyme. In contrast, no changes in the temperature stability of FeaB-Kp5.2 due to immobilization could be noted. However, relative enzyme activities towards all three substituted phenylacetaldehydes could be increased by the immobilization to approximately 130%. The most active and stable powdery immobilizate was MCF-G-Kw-FeaB-Kp5.2 at pH 8. In addition, FeaB-Kp5.2 was also immobilized and tested on monolith silica carrier for continuous catalysis to produce phenylacetic acids.

Arsenic is a toxic metalloid. It is released to the environment normally as arsenite [As(III)], largely due to mining activities. As(III) is more toxic and in many acidic mining environments more mobile than arsenate [As(V)] and therefore the oxidation of As(III) to As(V) is fundamental to immobilize and treat arsenic waste. Here, we report on the isolation and the phenotypic as well as genomic characterization of a novel extremely acidophilic As(III)-oxidizing strain from Reiche Zeche, a former silver mining site (Freiberg, Germany). The isolated strain CJR1 was identified as Acidiphilium acidophilum by 99.7% 16S rRNA positions shared with the type strain A. acidophilum DSM 700 ^T and by the Type (Strain) Genome Server platform. The new isolate is able to grow lithoautotrophically with As(III) from pH 4.9 to 1.5 with an optimum around pH 2.0. However, growth and As(III) oxidation rates were improved by adding yeast extract. The genome of CJR1, with 5.17 Mbp, is considerably bigger than that of other Acidiphilium strains and comprises four circular plasmids. The genome suggests the presence of the Calvin–Benson–Bassham cycle of multiple arsenic resistance operons ( ars ) and of an arsenite oxidase ( aio ). Graphical Abstract The representation of the genome seen on the graphical abstract was made using GenoVi [1].