Exploring the biochemical and biocatalytic properties of bacterial DyP-type peroxidases

This thesis describes the research on two dye decolorizing peroxidases (DyP-type peroxidases). As the name of this enzyme family suggests, are these enzyme involved in the decolorization and degradation of in water soluble dyes. The textile and food industries are potential application fields of this enzyme family. The main goal of the research described in this thesis was to increase the knowledge on DyP-type peroxidases. Two bacterial enzymes were selected as model enzymes: TfuDyP from Thermobifida fusca and SviDyP from Saccharomonospora viridis. First, we studied on which compounds TfuDyP is active. This work showed that the enzyme is, among other compounds, active on phenols and a large variety of dyes, including dyes that were not studied before using DyP-type peroxidases (chapter 2). Furthermore, the reaction mechanism of the enzyme was studied (chapter 3). For the industrial applicability of enzymes an easy production method with a high enzyme yield is required. Chapter 4 describes a study aimed at optimizing the production of active TfuDyP. To be active, DyP-type peroxidases need to bind a heme cofactor. Results presented in chapter 4 provide crucial information on what can go wrong with the heme cofactor when a heme-containing protein is overexpressed (produced). Finally we fused SviDyP to four different oxidases (another type of enzyme) to perform two-step cascade reactions (chapter 5). With these fusion enzymes we were able to produce the taste enhancer divanilline and to detect the sugars xylitol and cellobiose in a solution

Effective Hamiltonian with holomorphic variables

The pure-quantum self-consistent harmonic approximation (PQSCHA) permits to study a quantum system by means of an effective classical Hamiltonian - depending on quantum coupling and temperature - and classical-like expressions for the averages of observables. In this work the PQSCHA is derived in terms of the holomorphic variables connected to a set of bosonic operators. The holomorphic formulation, based on the path integral for the Weyl symbol of the density matrix, makes it possible to approach directly general Hamiltonians given in terms of bosonic creation and annihilation operators.Comment: 11 pages, no figures (2nd version: few mistakes fixed in Sects. IV-V

Effective Hamiltonian with holomorphic variables

The pure-quantum self-consistent harmonic approximation (PQSCHA) permits to study a quantum system by means of an effective classical Hamiltonian. In this work the PQSCHA is reformulated in terms of the holomorphic variables connected to a set of bosonic operators. The holomorphic formulation, based on the olomorphic path integral for the Weyl symbol of the density matrix, makes it possible to directly approach general Hamiltonians given in terms of bosonic creation and annihilation operators.Comment: Proceedings of the Conference "Path Integrals from peV to TeV - 50 Years from Feynman's paper" (Florence, August 1998) -- 2 pages, ReVTe

Hierarchical Mean-Field Theories in Quantum Statistical Mechanics

We present a theoretical framework and a calculational scheme to study the coexistence and competition of thermodynamic phases in quantum statistical mechanics. The crux of the method is the realization that the microscopic Hamiltonian, modeling the system, can always be written in a hierarchical operator language that unveils all symmetry generators of the problem and, thus, possible thermodynamic phases. In general one cannot compute the thermodynamic or zero-temperature properties exactly and an approximate scheme named ``hierarchical mean-field approach'' is introduced. This approach treats all possible competing orders on an equal footing. We illustrate the methodology by determining the phase diagram and quantum critical point of a bosonic lattice model which displays coexistence and competition between antiferromagnetism and superfluidity.Comment: 4 pages, 2 psfigures. submitted Phys. Rev.

The impact of carbon to nitrogen ratios and pH on the microbial prevalence and polyhydroxybutyrate production levels using a mixed microbial starter culture

Growth conditions have been frequently studied in optimizing polyhydroxybutyrate (PHB) production, while few studies were performed to unravel the dynamic mixed microbial consortia (MMCs) in the process. In this study, the relationship between growth conditions (C/N ratios and pH) and the corresponding key-microbes were identified and monitored during PHB accumulation. The highest PHB level (70 wt% of dry cell mass) was obtained at pH 9, C/N 40, and acetic acid 10 g/L. Linking the dominant genera with the highest point of PHB accumulation, Thauera was the most prevalent species in all MMCs of pH 9, except when a C/N ratio of 1 was applied. Notably, dominant bacteria shifted at pH 7 (C/N 10) from Thauera (0 h) to Paracoccus, and subsequently to Alcaligenes following the process of PHB accumulation and consumption. Further understanding of the relationship between the structure of the microbial community and the performance will be beneficial for regulating and obtaining high PHB accumulation within an MMC. Our study illustrates the impact of C/N ratios and pH on microbial prevalence and PHB production levels using a mixed microbial starter culture. This knowledge will broaden industrial perspectives for regulating high PHB production and timely harvesting