Biochemical Characterization of Phenylacetaldehyde Dehydrogenases from Styrene-degrading Soil Bacteria.

Four phenylacetaldehyde dehydrogenases (designated as FeaB or StyD) originating from styrene-degrading soil bacteria were biochemically investigated. In this study, we focused on the Michaelis-Menten kinetics towards the presumed native substrate phenylacetaldehyde and the obviously preferred co-substrate NAD+. Furthermore, the substrate specificity on four substituted phenylacetaldehydes and the co-substrate preference were studied. Moreover, these enzymes were characterized with respect to their temperature as well as long-term stability. Since aldehyde dehydrogenases are known to show often dehydrogenase as well as esterase activity, we tested this capacity, too. Almost all results showed clearly different characteristics between the FeaB and StyD enzymes. Furthermore, FeaB from Sphingopyxis fribergensis Kp5.2 turned out to be the most active enzyme with an apparent specific activity of 17.8 ± 2.1 U mg-1. Compared with that, both StyDs showed only activities less than 0.2 U mg-1 except the overwhelming esterase activity of StyD-CWB2 (1.4 ± 0.1 U mg-1). The clustering of both FeaB and StyD enzymes with respect to their characteristics could also be mirrored in the phylogenetic analysis of twelve dehydrogenases originating from different soil bacteria.

Reconstruction of the Metabolic Potential of Acidophilic Sideroxydans Strains from the Metagenome of an Microaerophilic Enrichment Culture of Acidophilic Iron-Oxidizing Bacteria from a Pilot Plant for the Treatment of Acid Mine Drainage Reveals Metabolic Versatility and Adaptation to Life at Low pH.

Bacterial community analyses of samples from a pilot plant for the treatment of acid mine drainage (AMD) from the lignite-mining district in Lusatia (East Germany) had previously demonstrated the dominance of two groups of acidophilic iron oxidizers: the novel candidate genus "Ferrovum" and a group comprising Gallionella-like strains. Since pure culture had proven difficult, previous studies have used genome analyses of co-cultures consisting of "Ferrovum" and a strain of the heterotrophic acidophile Acidiphilium in order to obtain insight into the life style of these novel bacteria. Here we report on attempts to undertake a similar study on Gallionella-like acidophiles from AMD. Isolates belonging to the family Gallionellaceae are still restricted to the microaerophilic and neutrophilic iron oxidizers Sideroxydans and Gallionella. Availability of genomic or metagenomic sequence data of acidophilic strains of these genera should, therefore, be relevant for defining adaptive strategies in pH homeostasis. This is particularly the case since complete genome sequences of the neutrophilic strains G. capsiferriformans ES-2 and S. lithotrophicus ES-1 permit the direct comparison of the metabolic capacity of neutrophilic and acidophilic members of the same genus and, thus, the detection of biochemical features that are specific to acidophilic strains to support life under acidic conditions. Isolation attempts undertaken in this study resulted in the microaerophilic enrichment culture ADE-12-1 which, based on 16S rRNA gene sequence analysis, consisted of at least three to four distinct Gallionellaceae strains that appear to be closely related to the neutrophilic iron oxidizer S. lithotrophicus ES-1. Key hypotheses inferred from the metabolic reconstruction of the metagenomic sequence data of these acidophilic Sideroxydans strains include the putative role of urea hydrolysis, formate oxidation and cyanophycin decarboxylation in pH homeostasis.