Modelling of the Corynebacterium glutamicum biosynthesis under aerobic fermentation conditions

This work concerns the modelling of the Corynebacterium glutamicum biosynthesis. At the beginning, the impulsive growth model of C. glutamicum under glutamate inhibition is established. According to this model, the analysis of the bioprocess stability is presented. Then, new objective functions are proposed and optimisation of C. glutamicum growth is presented. The results of the optimisation indicate that, although the growth of C. glutamicum is an aerobic process, the maximum of biomass productivity occurs under controlled penetration into the area of aerobic fermentation. Analytical results presented in this work are validated by numerical simulations.     

Biosynthetic Gene Cluster of Cetoniacytone A,an Unusual Aminocyclitol from the Endosymbiotic Bacterium Actinomyces sp. Lu 9419

A gene cluster responsible for the biosynthesis of the antitumor agent cetoniacytone A was identified in Actinomyces sp. strain Lu 9419, an endosymbiotic bacterium isolated from the intestines of the rose chafer beetle (Cetonia aurata). The nucleotide sequence analysis of the 46 kb DNA region revealed the presence of 31 complete ORFs, including genes predicted to encode a 2‐epi‐5‐epi‐valiolone synthase (CetA), a glyoxalase/bleomycin resistance protein (CetB), an acyltransferase (CetD), an FAD‐dependent dehydrogenase (CetF2), two oxidoreductases (CetF1 and CetG), two aminotransferases (CetH and CetM), and a pyranose oxidase (CetL). CetA has previously been demonstrated to catalyze the cyclization of sedoheptulose 7‐phosphate to the cyclic intermediate, 2‐epi‐5‐epi‐valiolone. In this report, the glyoxalase/bleomycin resistance protein homolog CetB was identified as a 2‐epi‐5‐epi‐valiolone epimerase (EVE), a new member of the vicinal oxygen chelate (VOC) superfamily. The 24 kDa recombinant histidine‐tagged CetB was found to form a homodimer; each monomer contains two βαβββ scaffolds that form a metal binding site with two histidine and two glutamic acid residues. A BLAST search using the newly isolated cet biosynthetic genes revealed an analogous suite of genes in the genome of Frankia alni ACN14a, suggesting that this plant symbiotic nitrogen‐fixing bacterium is capable of producing a secondary metabolite related to the cetoniacytones.     

An Ester of β-Hydroxybutyrate Regulates Cholesterol Biosynthesis in Rats and a Cholesterol Biomarker in Humans

In response to carbohydrate deprivation or prolonged fasting the ketone bodies, β‐hydroxybutyrate (βHB) and acetoacetate (AcAc), are produced from the incomplete β‐oxidation of fatty acids in the liver. Neither βHB nor AcAc are well utilized for synthesis of sterols or fatty acids in human or rat liver. To study the effects of ketones on cholesterol homeostasis a novel βHB ester (KE) ((R)‐3‐hydroxybutyl (R)‐3‐hydroxybutyrate) was synthesized and given orally to rats and humans as a partial dietary carbohydrate replacement. Rats maintained on a diet containing 30‐energy % as KE with a concomitant reduction in carbohydrate had lower plasma cholesterol and mevalonate (?40 and ?27 %, respectively) and in the liver had lower levels of the mevalonate precursors acetoacetyl‐CoA and HMG‐CoA (?33 and ?54 %) compared to controls. Whole liver and membrane LDL‐R as well as SREBP‐2 protein levels were higher (+24, +67, and +91 %, respectively). When formulated into a beverage for human consumption subjects consuming a KE drink (30‐energy %) had elevated plasma βHB which correlated with decreased mevalonate, a liver cholesterol synthesis biomarker. Partial replacement of dietary carbohydrate with KE induced ketosis and altered cholesterol homeostasis in rats. In healthy individuals an elevated plasma βHB correlated with lower plasma mevalonate.     

Aryl Bis‐Sulfonamide Inhibitors of IspF from Arabidopsis thaliana and Plasmodium falciparum

2‐Methylerythritol 2,4‐cyclodiphosphate synthase (IspF) is an essential enzyme for the biosynthesis of isoprenoid precursors in plants and many human pathogens. The protein is an attractive target for the development of anti‐infectives and herbicides. Using a photometric assay, a screen of 40 000 compounds on IspF from Arabidopsis thaliana afforded symmetrical aryl bis‐sulfonamides that inhibit IspF from A. thaliana (AtIspF) and Plasmodium falciparum (PfIspF) with IC₅₀ values in the micromolar range. The ortho‐bis‐sulfonamide structural motif is essential for inhibitory activity. The best derivatives obtained by parallel synthesis showed IC₅₀ values of 1.4 μm against PfIspF and 240 nm against AtIspF. Substantial herbicidal activity was observed at a dose of 2 kg ha^?1. Molecular modeling studies served as the basis for an in silico search targeted at the discovery of novel, non‐symmetrical sulfonamide IspF inhibitors. The designed compounds were found to exhibit inhibitory activities in the double‐digit micromolar IC₅₀ range.     

Starting to Gel: How Arabidopsis Seed Coat Epidermal Cells Produce Specialized Secondary Cell Walls

For more than a decade, the Arabidopsis seed coat epidermis (SCE) has been used as a model system to study the synthesis, secretion and modification of cell wall polysaccharides, particularly pectin. Our detailed re-evaluation of available biochemical data highlights that Arabidopsis seed mucilage is more than just pectin. Typical secondary wall polymers such as xylans and heteromannans are also present in mucilage. Despite their low abundance, these components appear to play essential roles in controlling mucilage properties, and should be further investigated. We also provide a comprehensive community resource by re-assessing the mucilage phenotypes of almost 20 mutants using the same conditions. We conduct an in-depth functional evaluation of all the SCE genes described in the literature and propose a revised model for mucilage production. Further investigation of SCE cells will improve our understanding of plant cell walls.