New light on ancient enzymes - in vitro CO Fixation by Pyruvate Synthase of Desulfovibrio africanus and Sulfolobus acidocaldarius.

Two variants of the enzyme family pyruvate:ferredoxin oxidoreductase (PFOR), derived from the anaerobic sulfate-reducing bacterium Desulfovibrio africanus and the extremophilic crenarchaeon Sulfolobus acidocaldarius, respectively, were evaluated for their capacity to fixate CO in vitro. PFOR reversibly catalyzes the conversion of acetyl-CoA and CO to pyruvate using ferredoxin as redox partner. The oxidative decarboxylation of pyruvate is thermodynamically strongly favored, and most previous studies only considered the oxidative direction of the enzyme.

Model-based derivation, analysis and control of unstable microaerobic steady-states--considering Rhodospirillum rubrum as an example.

Microaerobic (oxygen-limited) conditions are critical for inducing many important microbial processes in industrial or environmental applications. At very low oxygen concentrations, however, the process performance often suffers from technical limitations. Available dissolved oxygen measurement techniques are not sensitive enough and thus control techniques, that can reliable handle these conditions, are lacking.

Quorum sensing influences growth and photosynthetic membrane production in high-cell-density cultivations of Rhodospirillum rubrum.

Background: The facultative anoxygenic photosynthetic bacterium Rhodospirillum rubrum exhibits versatile metabolic activity allowing the adaptation to rapidly changing growth conditions in its natural habitat, the microaerobic and anoxic zones of stagnant waters. The microaerobic growth mode is of special interest as it allows the high-level expression of photosynthetic membranes when grown on succinate and fructose in the dark, which could significantly simplify the industrial production of compounds associated with PM formation. However, recently we showed that PM synthesis is no longer inducible when R.

Stepwise reduction of the culture redox potential allows the analysis of microaerobic metabolism and photosynthetic membrane synthesis in Rhodospirillum rubrum.

Bacterial growth under oxygen-limited (microaerobic) conditions is often accompanied by phenomena of great interest for fundamental research and industrial application. The microaerobic lifestyle of anoxygenic photosynthetic bacteria like Rhodospirillum rubrum harbors such a phenomenon, as it allows the formation of photosynthetic membranes and related interesting products without light. However, due to the technical difficulties in process control of microaerobic cultivations and the limited sensitivity of available oxygen sensors, the analysis of microaerobic growth and physiology is still underrepresented in current research.

High-level production of the industrial product lycopene by the photosynthetic bacterium Rhodospirillum rubrum.

The biosynthesis of the major carotenoid spirilloxanthin by the purple nonsulfur bacterium Rhodospirillum rubrum is thought to occur via a linear pathway proceeding through phytoene and, later, lycopene as intermediates. This assumption is based solely on early chemical evidence (B. H.

Fructose metabolism of the purple non-sulfur bacterium Rhodospirillum rubrum: effect of carbon dioxide on growth, and production of bacteriochlorophyll and organic acids.

During fermentative metabolism, carbon dioxide fixation plays a key role in many bacteria regarding growth and production of organic acids. The present contribution, dealing with the facultative photosynthetic bacterium Rhodospirillum rubrum, reveals not only the strong influence of ambient carbon dioxide on the fermentative break-down of fructose but also a high impact on aerobic growth with fructose as sole carbon source. Both growth rates and biomass yield increased with increasing carbon dioxide supply in chemoheterotrophic aerobic cultures.

Metabolic network modeling of redox balancing and biohydrogen production in purple nonsulfur bacteria.

Background: Purple nonsulfur bacteria (PNSB) are facultative photosynthetic bacteria and exhibit an extremely versatile metabolism. A central focus of research on PNSB dealt with the elucidation of mechanisms by which they manage to balance cellular redox under diverse conditions, in particular under photoheterotrophic growth.

Results: Given the complexity of the central metabolism of PNSB, metabolic modeling becomes crucial for an integrated analysis of the accumulated biological knowledge.

A glutathione redox effect on photosynthetic membrane expression in Rhodospirillum rubrum.

The formation of intracytoplasmic photosynthetic membranes by facultative anoxygenic photosynthetic bacteria has become a prime example for exploring redox control of gene expression in response to oxygen and light. Although a number of redox-responsive sensor proteins and transcription factors have been characterized in several species during the last several years in some detail, the overall understanding of the metabolic events that determine the cellular redox environment and initiate redox signaling is still poor. In the present study we demonstrate that in Rhodospirillum rubrum, the amount of photosynthetic membranes can be drastically elevated by external supplementation of the growth medium with the low-molecular-weight thiol glutathione.

Model-based high cell density cultivation of Rhodospirillum rubrum under respiratory dark conditions.

The potential of facultative photosynthetic bacteria as producers of photosynthetic pigments, vitamins, coenzymes and other valuable products has been recognized for decades. However, mass cultivation under photosynthetic conditions is generally inefficient due to the inevitable limitation of light supply when cell densities become very high. The previous development of a new cultivation process for maximal expression of photosynthetic genes under semi-aerobic dark conditions in common bioreactors offers a new perspective for utilizing the facultative photosynthetic bacterium Rhodospirillum rubrum for large-scale applications.

Redox-state dynamics of ubiquinone-10 imply cooperative regulation of photosynthetic membrane expression in Rhodospirillum rubrum.

It is now well established that, for photosynthetic bacteria, the aerobic-to-microaerophilic transition activates the membrane-bound sensor kinase RegB, which subsequently phosphorylates the transcriptional activator RegA, thereby inducing elevated levels of intracellular photosynthetic membranes. The mechanism of RegB activation--in particular, the role of ubiquinone-10--is controversial at present. One problem here is that very limited quantitative in vivo data for the response of the ubiquinone redox state to different cultivation conditions exist.

Modeling the electron transport chain of purple non-sulfur bacteria.

Purple non-sulfur bacteria (Rhodospirillaceae) have been extensively employed for studying principles of photosynthetic and respiratory electron transport phosphorylation and for investigating the regulation of gene expression in response to redox signals. Here, we use mathematical modeling to evaluate the steady-state behavior of the electron transport chain (ETC) in these bacteria under different environmental conditions. Elementary-modes analysis of a stoichiometric ETC model reveals nine operational modes.

Profiling of external metabolites during production of hantavirus nucleocapsid protein with recombinant Saccharomyces cerevisiae.

Recombinant strains of Saccharomyces cerevisiae, producing hantavirus Puumala nucleocapsid protein for diagnostics and as a candidate vaccine were analyzed for uptake and excretion of intermediary metabolites during process optimization studies of fed-batch bioreactor cultures. Concentrations of glucose, maltose, galactose, pyruvate, acetaldehyde, ethanol, acetate, succinate and formaldehyde (used as a selection agent) were measured in the culture medium in order to find a metabolite pattern, indicative for the physiological state of the producer culture. When the inducer galactose was employed as a growth substrate, the metabolite profile of recombinant yeast cells was different from those of the non-recombinant original strain which excreted considerable amounts of metabolites with this substrate.

Microaerophilic cooperation of reductive and oxidative pathways allows maximal photosynthetic membrane biosynthesis in Rhodospirillum rubrum.

The purple nonsulfur bacterium Rhodospirillum rubrum has been employed to study physiological adaptation to limiting oxygen tensions (microaerophilic conditions). R. rubrum produces maximal levels of photosynthetic membranes when grown with both succinate and fructose as carbon sources under microaerophilic conditions in comparison to the level (only about 20% of the maximum) seen in the absence of fructose.