Investigating microbial interactions from an ecological perspective is a particularly fruitful approach to unveil both new chemistry and bioactivity. Microbial predator-prey interactions in particular rely on natural products as signal or defense molecules. In this context, we identified a grazing-resistant strain, isolated from the bacterivorous amoeba Genome analysis of this bacterium revealed the presence of two biosynthetic gene clusters that were found adjacent to each other on a contiguous stretch of the bacterial genome. Although one cluster codes for the polyketide synthase producing the known antibiotic mupirocin, the other cluster encodes a nonribosomal peptide synthetase leading to the unreported cyclic lipopeptide jessenipeptin. We describe its complete structure elucidation, as well as its synergistic activity against methicillin-resistant , when in combination with mupirocin. Both biosynthetic gene clusters are regulated by quorum-sensing systems, with 3-oxo-decanoyl homoserine lactone (3-oxo-C10-AHL) and hexanoyl homoserine lactone (C6-AHL) being the respective signal molecules. This study highlights the regulation, richness, and complex interplay of bacterial natural products that emerge in the context of microbial competition.

Background: Propionyl-CoA is a common metabolic intermediate that requires degradation to avoid intoxication of cellular metabolism. Results: A key enzyme involved in a modified ␤-oxidation pathway in Candida albicans has been identified. Conclusion: Although fungi generally use the methyl citrate cycle to degrade propionyl-CoA, CUG clade yeasts form an exception. Significance: The modified ␤-oxidation pathway could provide a target for new antifungal compounds.

In this study, a precise and reliable ultra-high performance liquid chromatography (UHPLC) method for the simultaneous determination of non-canonical (norvaline and norleucine) and standard amino acids (aspartic acid, glutamic acid, serine, histidine, glycine, threonine, arginine, tyrosine, methionine, valine, phenylalanine, isoleucine, leucine) in biopharmaceutical-related fermentation processes was established. After pre-column derivatization with ortho-phthaldialdehyde and 2-mercaptoethanol, the derivatives were separated on a sub-2 μm particle C18 reverse-phase column. Identification and quantification of amino acids were carried out by fluorescence detection. To test method feasibility on standard HPLC instruments, the assay was properly transferred to a core–shell particle C18 reverse-phase column. The limits of detection showed excellent sensitivity by values from 0.06 to 0.17 pmol per injection and limits of quantification between 0.19 and 0.89 pmol. In the present study, the newly established UHPLC method was applied to a recombinant antibody Escherichia coli fermentation process for the analysis of total free amino acids. We were able to specifically detect and quantify the unfavorable amino acids in such complex samples. Since we observed trace amounts of norvaline and norleucine during all fermentation phases, an obligatory process monitoring should be considered to improve quality of recombinant protein drugs in future.

BackgroundNorleucine and norvaline belong to a group of non-canonical amino acids which are synthesized as byproducts in the branched chain amino acid metabolism of Escherichia coli. The earlier observed misincorporation of these rare amino acids into recombinant proteins has attracted increasing attention due to the rising use of protein based biopharmaceuticals in clinical application. Experimental data revealed pyruvate overflow inducing conditions, which typically occur in oxygen limited zones of large-scale fermentations as a major reason leading to norvaline and norleucine synthesis during E. coli cultivation. Previous approaches to suppress misincorporation of norleucine and norvaline considered growth media supplementation with the relevant canonical isostructural compounds, but no research was performed on the impact of the overflow metabolism related trace elements molybdenum, nickel and selenium. These elements form essential parts of the formate hydrogen lyase (FHL) metalloprotein complex, which is a key enzyme of anaerobic pyruvate metabolism in E. coli and could therefore represent a crucial connection to the pyruvate accumulation associated biosynthesis of rare amino acids.ResultsIn this study, the trace element associated response of recombinant antibody producing E. coli to oxygen limitation at high glucose concentration with a special focus on non-canonical amino acids was analysed. During fed-batch cultivation with provoked oxygen limitation and glucose excess norleucine and norvaline were only accumulated in the absence of molybdenum, nickel and selenium. In contrast, the trace element supplemented stress fermentation showed significantly reduced concentrations of these rare amino acids and the major signature fermentation product formate, supporting the correlation between a functional formate hydrogen lyase complex and low unspecific amino acid synthesis under oxygen limitation at high glucose concentration.ConclusionsThe formation of norleucine and norvaline by recombinant E. coli during cultivation with provoked oxygen limitation and glucose excess can be reduced to levels at the detection limit by adding the trace elements molybdenum, selenium and nickel to the fermentation medium. Even under the metabolic burden during induction phase the physiologically available concentrations of non-canonical amino acids remained low. Since our results allow facile process changes that can be easily implemented to avoid the undesirable accumulation of norleucine and norvaline, we consider this study highly interesting for improved process development in E. coli based recombinant drug production and the future development of possible mechanisms to reduce misincorporation events into protein based biopharmaceuticals.

Hydrogen-mediated microbial electrosynthesis with Clostridium ljungdahlii enabled the metabolic flux diversification from acetate to glycine and ethanolamine.

No abstract

Electroautotrophy is a novel and fascinating microbial metabolism, with tremendous potential for CO 2 storage and valorization into chemicals and materials made thereof. Research attention has been devoted toward the characterization of acetogenic and methanogenic electroautotrophs. In contrast, here we characterize the electrophysiology of a sulfate-reducing bacterium, Desulfosporosinus orientis, harboring the Wood-Ljungdahl pathway and, thus, capable of fixing CO 2 into acetyl-CoA. For most electroautotrophs the mode of electron uptake is still not fully clarified. Our electrochemical experiments at different polarization conditions and Fe 0 corrosion tests point to a H 2-mediated electron uptake ability of this strain. This observation is in line with the lack of outer membrane and periplasmic multi-heme c-type cytochromes in this bacterium. Maximum planktonic biomass production and a maximum sulfate reduction rate of 2 ± 0.4 mM day −1 were obtained with an applied cathode potential of −900 mV vs. Ag/AgCl, resulting in an electron recovery in sulfate reduction of 37 ± 1.4%. Anaerobic sulfate respiration is more thermodynamically favorable than acetogenesis. Nevertheless, D. orientis strains adapted to sulfate-limiting conditions, could be tuned to electrosynthetic production of up to 8 mM of acetate, which compares well with other electroacetogens. The yield per biomass was very similar to H 2 /CO 2 based acetogenesis. Acetate bioelectrosynthesis was confirmed through stable isotope labeling experiments with Na-H 13 CO 3. Our results highlight a great influence of the CO 2 feeding strategy and start-up H 2 level in the catholyte on planktonic biomass growth and acetate production. In serum bottles experiments, D. orientis also generated butyrate, which makes D. orientis even more attractive for bioelectrosynthesis application. A further optimization of these physiological pathways is needed to obtain electrosynthetic butyrate production in D. orientis biocathodes. This study expands the diversity of facultative autotrophs able to perform H 2-mediated extracellular electron uptake in Bioelectrochemical Systems (BES). We characterized a sulfate-reducing and acetogenic bacterium, D. orientis, able to naturally produce acetate and butyrate

No abstract