Formation of allyl isothiocyanate from sinigrin in the digestive tract of rats monoassociated with a human colonic strain of Bacteroides thetaiotaomicron.

A human digestive strain of Bacteroides thetaiotaomicron was tested for its ability to metabolise sinigrin, a glucosinolate commonly found in Brassica vegetables. Gnotobiotic rats harbouring the bacterial strain were orally dosed with 50 micromol sinigrin. HPLC analysis of the digestive contents showed that sinigrin was degraded in the large bowel, where B. thetaiotaomicron was established at a high level. Concurrently, a hydrolysis product of sinigrin, allyl isothiocyanate, was identified by GC-MS analysis, following headspace solid-phase microextraction of the digestive contents; its production peaked at ca. 200 nmol, 12 h after dosing. This is the first study to demonstrate in vivo the involvement of a human colonic predominant bacterium in the bioconversion of a dietary glucosinolate to a potentially anticarcinogenic isothiocyanate.

Cleavage of L-leucine-containing dipeptides by Clostridium butyricum.

The ability of Clostridium butyricum cultures to hydrolyze three L-leucine-containing dipeptides (Leu-Leu, Leu-Gly and Gly-Leu) in a synthetic minimal medium is demonstrated by using gas chromatography coupled with mass spectrometry. The 13C nuclear magnetic resonance and a labeled dipeptide L-[1-13C]Leu-Gly were used to confirm this activity.

Synthesis of 2-hydroxy acid from 2-amino acid by Clostridium butyricum.

Cultures of Clostridium butyricum type strain in synthetic medium supplemented with various L-2-amino acids revealed the presence of the corresponding 2-hydroxy acid. This metabolite is able to produce the polyester poly(2-hydroxyalkanoic acid). The bioconversion is not stereoselective since D-2-amino acids were also converted. Chiral GC analysis demonstrated that only D-enantiomer is formed from L-leucine.

Refractometer for tracking changes in the refractive index of air near 780 nm.

A new system, consisting of a double-channel Fabry-Perot etalon and laser diodes emitting around 780 nm, is described and proposed for use for measuring air-refractive index. The principle of this refractometer is based on frequency measurements between optical laser sources. It permits quasi-instantaneous measurement with a resolution of better than 10(-9) and uncertainty in the 10(-8) range. Some preliminary results on the stability of this system and the measurements of the refractive index of air with this apparatus are presented. The first measurements of the index of air at 780 nm are, within an experimental uncertainty of the order of 2 x 10(-8), in agreement with the predicted values by the so-called revised Edlén equations. This result is, to the best of our knowledge, the first to extend to the near IR the validity of the revised Edlén equation derived for the wavelength range of 350-650 nm.