Styrene monooxygenases, indole monooxygenases and related flavoproteins applied in bioremediation and biocatalysis.

Styrene and indole are naturally occurring compounds, which are also produced and processed by various chemical industries. Thus, it is not surprisingly that microorganisms evolved pathways to detoxify or even to utilize those compounds as carbon sources. Especially, among bacteria several routes are described specifically for the activation and degradation of styrene and indole. Respectively, the initial attack toward these compounds occurs via a flavin-dependent monooxygenase: styrene monooxygenase (SMO) or indole monooxygenase (IMO). In the first place, SMOs have been described to initiate a styrene specific degradation. These are in general two-component systems, whereas a small FAD-reductase (SMOB) delivers reduced FAD on the expense of NADH toward the monooxygenase (SMOA). Various modes of interaction are possible and for both mostly dimeric protein subunits structural data were reported. Thus, this flavoprotein monooxygenase-especially the one from Pseudomonas putida S12 can be seen as the prototype of this class of enzymes. In the course of describing related members of this enzyme family some remarkable findings were made. For example, self-sufficient fusion proteins have been reported as well as enzymes, which could not be assigned to a styrene metabolic activity, rather to indole conversion. Later it was found that this flavoprotein group can be separated at least into two subgroups: styrene and indole monooxygenases. And both enzymes rely on a FAD-reductase to obtain the reduced cofactor (FADred), which is employed to activate molecular oxygen toward hydroperoxy-FAD, which allows substrate epoxidation and the formation of hydroxy-FAD, which finally yields H2O and oxidized FAD.

Effects of Organic Solvents on Indigo Formation by Pseudomonas sp. strain ST-200 Grown with High Levels of Indole.

The indole tolerance level of Pseudomonas sp. strain ST-200 was 0.25 mg/ml. The level was raised to 4 mg/ml when diphenylmethane was added to the medium to 20% by volume. ST-200 grown in this two-phase culture system containing indole (1 mg/ml) and diphenylmethane (0.2 ml/ml) produced a water-soluble yellow pigment, isatic acid, and two water-insoluble and diphenylmethane-soluble pigments, blue indigo and purple indirubin. The amounts of the water-insoluble pigments corresponded to 0.5% (indigo) and 0.2% (indirubin) of the indole added to the medium. Of the conditions tried, indigo and indirubin were formed only when ST-200 was grown in the two-phase system overlaid with organic solvents with appropriate polarity.