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Volkers R.J.M.,Wageningen University | Volkers R.J.M.,Kluyver Center for Genomics of Industrial Fermentation | Snoek L.B.,Technical University of Delft | Ruijssenaars H.J.,Corbion | And 2 more authors.
PLoS ONE | Year: 2015

Pseudomonas putida S12 is exceptionally tolerant to various organic solvents. To obtain further insight into this bacterium's primary defence mechanisms towards these potentially harmful substances, we studied its genome wide transcriptional response to sudden addition of toluene. Global gene expression profiles were monitored for 30 minutes after toluene addition. During toluene exposure, high oxygen-affinity cytochrome c oxidase is specifically expressed to provide for an adequate proton gradient supporting solvent efflux mechanisms. Concomitantly, the glyoxylate bypass route was up-regulated, to repair an apparent toluene stress-induced redox imbalance. A knock-out mutant of trgI, a recently identified toluene-repressed gene, was investigated in order to identify TrgI function. Remarkably, upon addition of toluene the number of differentially expressed genes initially wasmuch lower in the trgI-mutant than in the wild-type strain. This suggested that after deletion of trgI cells were better prepared for sudden organic solvent stress. Before, as well as after, addition of toluene many genes of highly diverse functions were differentially expressed in trgI-mutant cells as compared to wild-type cells. This led to the hypothesis that TrgI may not only be involved in the modulation of solvent-elicited responses but in addition may affect basal expression levels of large groups of genes. © 2015 Volkers et al. Source


Bosma E.F.,Wageningen University | van de Weijer A.H.P.,Wageningen University | Daas M.J.A.,Wageningen University | van der Oost J.,Wageningen University | And 2 more authors.
Applied and Environmental Microbiology | Year: 2015

Thermophilic bacteria are regarded as attractive production organisms for cost-efficient conversion of renewable resources to green chemicals, but their genetic accessibility is a major bottleneck in developing them into versatile platform organisms. In this study, we aimed to isolate thermophilic, facultatively anaerobic bacilli that are genetically accessible and have potential as platform organisms. From compost, we isolated 267 strains that produced acids from C5 and C6 sugars at temperatures of 55°C or 65°C. Subsequently, 44 strains that showed the highest production of acids were screened for genetic accessibility by electroporation. Two Geobacillus thermodenitrificans isolates and one Bacillus smithii isolate were found to be transformable with plasmid pNW33n. Of these, B. smithii ET 138 was the best-performing strain in laboratory-scale fermentations and was capable of producing organic acids from glucose as well as from xylose. It is an acidotolerant strain able to produce organic acids until a lower limit of approximately pH 4.5. As genetic accessibility of B. smithii had not been described previously, six other B. smithii strains from the DSMZ culture collection were tested for electroporation efficiencies, and we found the type strain DSM 4216T and strain DSM 460 to be transformable. The transformation protocol for B. smithii isolate ET 138 was optimized to obtain approximately 5×103 colonies per μg plasmid pNW33n. Genetic accessibility combined with robust acid production capacities on C5 and C6 sugars at a relatively broad pH range make B. smithii ET 138 an attractive biocatalyst for the production of lactic acid and potentially other green chemicals. © 2015, American Society for Microbiology. Source


Grewal N.,Kansas State University | Faubion J.,Kansas State University | Feng G.,Corbion | Kaufman R.C.,U.S. Department of Agriculture | And 2 more authors.
Journal of Agricultural and Food Chemistry | Year: 2015

Maltogenic α-amylase is widely used as an antistaling agent in bakery foods. The objective of this study was to determine the degree of hydrolysis (DH) and starch structure after maltogenic amylase treatments in relation to its retrogradation. Waxy maize starch was cooked and hydrolyzed to different degrees by a maltogenic amylase. High-performance anion-exchange chromatography and size exclusion chromatography were used to determine saccharides formed and the molecular weight (Mw) distributions of the residual starch structure, respectively. Chain length (CL) distributions of debranched starch samples were further related to amylopectin (AP) retrogradation. Differential scanning calorimetry (DSC) results showed the complete inhibition of retrogradation when starches were hydrolyzed to >20% DH. Mw and CL distributions of residual AP structure indicated that with an increase in %DH, a higher proportion of unit chains with degree of polymerization (DP) ≤9 and a lower proportion of unit chains with DP ≥17 were formed. A higher proportion of short outer AP chains that cannot participate in the formation of double helices supports the decrease in and eventual inhibition of retrogradation observed with the increase in %DH. These results suggest that the maltogenic amylase could play a powerful role in inhibiting the staling of baked products even at limited starch hydrolysis. © 2015 American Chemical Society. Source


Shahidi F.,Memorial University of Newfoundland | Zhong Y.,Corbion
Journal of Functional Foods | Year: 2015

Antioxidants play an important role in food preservation by inhibiting oxidation processes and contributing to health promotion rendered by many dietary supplements, nutraceuticals and functional food ingredients. Antioxidant activity can be monitored by a variety of assays with different mechanisms, including hydrogen atom transfer (HAT), single electron transfer (ET), reducing power, and metal chelation, among others. Understanding the principle mechanisms, advantages and limitations of the measurement assays is important for proper selection of method(s) for valid evaluation of antioxidant potential in desired applications. This contribution provides a general and up-to-date overview of methods available for measuring antioxidant activity and the chemistry behind them. © 2015. Source

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