Methods for quantification of growth and productivity in anaerobic microbiology and biotechnology

Anaerobic microorganisms (anaerobes) possess a fascinating metabolic versatility. This characteristic makes anaerobes interesting candidates for physiological studies and utilizable as microbial cell factories. To investigate the physiological characteristics of an anaerobic microbial population, yield, productivity, specific growth rate, biomass production, substrate uptake, and product formation are regarded as essential variables. The determination of those variables in distinct cultivation systems may be achieved by using different techniques for sampling, measuring of growth, substrate uptake, and product formation kinetics. In this review, a comprehensive overview of methods is presented, and the applicability is discussed in the frame of anaerobic microbiology and biotechnology.© The Author(s) 201

Physiology and methane productivity of Methanobacterium thermaggregans

Accumulation of carbon dioxide (CO2), associated with global temperature rise, and drastically decreasing fossil fuels necessitate the development of improved renewable and sustainable energy production processes. A possible route for CO2 recycling is to employ autotrophic and hydrogenotrophic methanogens for CO2-based biological methane (CH4) production (CO2-BMP). In this study, the physiology and productivity of Methanobacterium thermaggregans was investigated in fed-batch cultivation mode. It is shown that M. thermaggregans can be reproducibly adapted to high agitation speeds for an improved CH4 productivity. Moreover, inoculum size, sulfide feeding, pH, and temperature were optimized. Optimization of growth and CH4 productivity revealed that M. thermaggregans is a slightly alkaliphilic and thermophilic methanogen. Hitherto, it was only possible to grow seven autotrophic, hydrogenotrophic methanogenic strains in fed-batch cultivation mode. Here, we show that after a series of optimization and growth improvement attempts another methanogen, M. thermaggregas could be adapted to be grown in fed-batch cultivation mode to cell densities of up to 1.56 g L−1. Moreover, the CH4 evolution rate (MER) of M. thermaggregans was compared to Methanothermobacter marburgensis, the CO2-BMP model organism. Under optimized cultivation conditions, a maximum MER of 96.1 ± 10.9 mmol L−1 h−1 was obtained with M. thermaggregans—97% of the maximum MER that was obtained utilizing M. marburgensis in a reference experiment. Therefore, M. thermaggregans can be regarded as a CH4 cell factory highly suited to be applicable for CO2-BMP.© The Author(s) 201

The Center Problem for the Lotka Reactions with Generalized Mass-Action Kinetics

Chemical reaction networks with generalized mass-action kinetics lead to power-law dynamical systems. As a simple example, we consider the Lotka reactions and the resulting planar ODE. We characterize the parameters (positive coefficients and real exponents) for which the unique positive equilibrium is a center.© The Author(s) 201

Synthesis and in vivo anticancer evaluation of poly(organo)phosphazene-based metallodrug conjugates

Within this work we aimed to improve the pharmacodynamics and toxicity profile of organoruthenium and -rhodium complexes which had previously been found to be highly potent in vitro but showed unselective activity in vivo. Different organometallic complexes were attached to a degradable poly(organo)phosphazene macromolecule, prepared via controlled polymerization techniques. The conjugation to hydrophilic polymers was designed to increase the aqueous solubility of the typically poorly soluble metal-based half-sandwich compounds with the aim of a controlled, pH-triggered release of the active metallodrug. The synthesized conjugates and their characteristics have been thoroughly studied by means of 31P NMR and UV-Vis spectroscopy, ICP-MS analyses and SEC coupled to ICP-MS. In order to assess their potential as possible anticancer drug candidates, the complexes, as well as their respective macromolecular prodrug formulations were tested against three different cancer cell lines in cell culture. Subsequently, the anticancer activity and organ distribution of the poly(organo)phosphazene drug conjugates were explored in vivo in mice bearing CT-26 colon carcinoma. Our investigations revealed a beneficial influence of this macromolecular prodrug by a significant reduction of adverse effects compared to the free metallodrugs