Enantiomeric Natural Products: Occurrence and Biogenesis

In nature, chiral natural products are usually produced in optically pure form—however, occasionally both enantiomers are formed. These enantiomeric natural products can arise from a single species or from different genera and/or species. Extensive research has been carried out over the years in an attempt to understand the biogenesis of naturally occurring enantiomers; however, many fascinating puzzles and stereochemical anomalies still remain. Two sides to the story : The formation of enantiomerically opposite natural products by nature is known, although rare (see examples). To date, many puzzles and stereochemical anomalies remain regarding the biogenesis of these unique natural products, despite the substantial body of research that has been carried out over the years in an attempt to understand the biogenesis of enantiomeric metabolites.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92098/1/4802_ftp.pd

Enantiomere Naturstoffe: Vorkommen und Biogenese

In der Natur werden chirale Substanzen meist in enantiomerenreiner Form synthetisiert – manchmal entstehen aber auch beide Enantiomere. Solche enantiomeren Naturstoffe können von einer Art oder von verschiedenen Gattungen und/oder Arten gebildet werden. Intensive Forschungen wurden über viele Jahre durchgeführt, um die Biogenese natürlich vorkommender Enantiomere zu verstehen, doch viele faszinierende Rätsel und stereochemische Anomalien sind nach wie vor ungelöst. Bild und Spiegelbild in der Natur: Die Bildung von natürlich vorkommenden Enantiomerenpaaren ist bekannt, wenn auch selten (siehe Beispiel). Bis heute sind noch viele Rätsel und stereochemische Anomalien bei der Biogenese dieser einmaligen Naturstoffe ungelöst, auch wenn im Laufe der Jahre viel Arbeit investiert worden ist, um die Entstehung enantiomerer Metaboliten zu verstehen.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91315/1/4886_ftp.pd

Impact of the maize rhizosphere on the genetic structure, the diversity and the atrazine-degrading gene composition of cultivable atrazine-degrading communities

International audienceSixty-six atrazine-degrading bacterial communities utilizing atrazine as sole N source and citrate as principal C source were isolated from unplanted and maize planted soils treated with atrazine. Ribosomal intergenic spacer analysis (RISA) fingerprints revealed that the genetic structure of atrazine-degrading bacterial communities was modified in the maize rhizosphere. To assess the underlying microbial diversity, 16S rDNA sequences amplified from each bacterial community were cloned. Libraries containing 660 16S rDNA clones were screened by restriction fragment length polymorphism (RFLP) analysis. In all, 63 clone families were identified. Rarefaction curves did not reach a clear saturation, indicating that the analysis of a greater number of clones would have revealed further diversity. Recovered 16S rDNA sequences were related to Actinobacteria, Bacteroidetes and Proteobacteria. The four dominant RFLP families were highly similar to Variovorax paradoxus, Burkholderia cepacia, Arthrobacter sp. and Bosea sp. The composition of most of the atrazine-degrading bacterial communities consisted of 2–7 different bacterial species. Various atrazine-degrading gene compositions were observed, two of these atzABCDEF, trzND and atzBCDEF, trzN being largely dominant. The first was more frequently detected in bacterial communities isolated from the maize rhizosphere whereas the second was more frequently detected in communities isolated from bulk soil. Monitoring of atrazine-degrading activity showed that 76% of the bacterial communities degraded up to 80% of the initially added atrazine within 15 days of culture. Altogether our results indicate that the maize rhizosphere has an impact on the genetic structure, the diversity and atrazine-degrading gene composition of the atrazine-degrading communities

Montréal sur papier, premier volet = Montreal on Paper, Part One

Campbell adds a brief history of drawing to his analysis of individual works on paper by 15 Montreal artists. Statements by some of the artists. 10 bibl. ref

Séries Kompakt

Mayrand and Gilbert circumscribe the characteristics of serial works of reduced format. Texts by the 15 participating Montreal artists and reproduction of a text by Gascon accompanying the "Teknologia" book-object (Editions Graff, 1989). Brief biographical notes