Bacterial
trans
-acyltransferase polyketide synthases (
trans
-AT PKSs) are among the most complex known enzymes from secondary metabolism and are responsible for the biosynthesis of highly diverse bioactive polyketides. However, most of these metabolites remain uncharacterized, since
trans
-AT PKSs frequently Occur in poorly studied microbes and feature a remarkable array of non-canonical biosynthetic components with poorly understood functions. As a consequence, genome-guided natural product identification has been challenging. To enable
de novo
structural predictions for
trans
-AT PKS-derived polyketides, we developed the
Trans
-AT PKS Polyketide Predictor (TransATor). TransATor is a versatile bio- and chemoinformatics web application that suggests informative chemical structures for even highly aberrant
trans
-AT PKS biosynthetic gene clusters, thus permitting hypothesis-based, targeted biotechnological discovery and biosynthetic studies. We demonstrate the applicative scope in several examples, including the characterization of new variants of bioactive natural products as well as structurally novel polyketides from unusual bacterial sources.
The periodic extraction of a solute from an aqueous solution into a thin layer of an organic
solvent (extractant) and its back extraction into a second aqueous solution have been studied
experimentally. An aqueous solution of citric acid, whose temperature was cycled as a square
wave, was circulated through a bed of polypropylene pellets that were coated with a thin layer
of an organic solvent containing Alamine 336. The results indicate the following: (a) Periodic
extraction by means of a minute amount of extractant, spread on a suitable support material,
is feasible. (b) Frequent shallow penetration of the solute into the extractant layer is both feasible
and useful as it will intensify the overall average mass transport. (c) The penetration by diffusion
of the solute into deep layers of the extractant is too slow to affect the average overall mass
transfer. The results of this study should be applicable to liquid−liquid extraction systems using
a driving force other than thermal.
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