Direct production of L-tagatose from L-psicose by Enterobacter aerogenes 230S.

L-tagatose was produced directly from L-psicose by subjecting the same biomass suspension to microbial reduction followed by oxidation using a newly isolated bacteria Enterobacter aerogenes 230S. After various optimizations, it was observed that cells grown on xylitol have the best conversion potential. Moreover, E. aerogenes 230S converted L-psicose to L-tagatose at a faster rate in the presence of polyols such as glycerol, D-sorbitol, ribitol, L-arabitol, D-mannitol and xylitol. At 5% substrate concentration, the conversion ratio of L-psicose to L-tagatose was above 60% in the presence of glycerol. Identity of crystalline L-tagatose was confirmed by HPLC analysis, (13)C-NMR spectra, and optical rotation.

6-Azido-6-de-oxy-α-l-galactose (6-azido-l-fucose) monohydrate.

Although 6-azido-6-de-oxy-l-galactose in aqueous solution is in equilibrium between the open-chain, furan-ose and pyran-ose forms, it crystallizes solely as 6-azido-6-de-oxy-α-l-galactopyran-ose monohydrate, C(6)H(11)N(3)O(5)·H(2)O, with the six-membered ring adopting a chair conformation. The structure exists as hydrogen-bonded chains, with each mol-ecule acting as a donor and acceptor of five hydrogen bonds. There are no unusual crystal packing features and the absolute configuration was determined from the use of 1-azido-1-de-oxy-d-galactitol as the starting material.

Cloning, expression, and transcription analysis of L-arabinose isomerase gene from Mycobacterium smegmatis SMDU.

The L-arabinose metabolic gene cluster, araA, araB, araD, araG, araH and araR, encoding L-arabinose isomerase (L-AI) and its accessory proteins was cloned from Mycobacterium smegmatis SMDU and sequenced. The deduced amino acid sequence of araA displayed highest identity with that of Bacillus subtilis (52%). These six genes comprised the L-arabinose operon, and its genetic arrangement was similar to that of B. subtilis. The L-AI gene (araA), encoding a 501 amino acid protein with a calculated molecular mass of 54,888 Da, was expressed in Escherichia coli. The productivity and overall enzymatic properties of the recombinant L-AI were almost same as the authentic L-AI from M. smegmatis. Although the recombinant L-AI showed high substrate specificity, as did L-AI from other organisms, this enzyme catalyzed not only isomerization of L-arabinose-L-ribulose and D-galactose-D-tagatose but also isomerization of L-altrose-L-psicose and L-erythrulose-L-threose. In combination with L-AI from M. smegmatis, L-threose and L-altrose can be produced from cheap and abundant erythritol and D-fructose respectively, indicating that this enzyme has great potential for biological application in rare sugar production. Transcription analysis using various sugars revealed that this enzyme was significantly induced not only by L-arabinose and D-galactose but also by L-ribose, galactitol, L-ribulose, and L-talitol. This different result of transcription mediated by sugars from that of E. coli suggests that the transcriptional regulation of araA from M. smegmatis against sugar is loose compared with that from E. coli, and that it depends on the hydroxyl configuration at C2, C3 and C4 positions of sugars.

Bioproduction of D-psicose from allitol with Enterobacter aerogenes IK7: a new frontier in rare ketose production.

D-psicose, a new alternative sweetener, was produced from allitol by microbial oxidation of the newly isolated strain Enterobacter aerogenes IK7. Cells grown in tryptic soy broth medium (TSB) supplemented with D-mannitol at 37 degrees C were found to have the best oxidation potential. The cells, owing to broad substrate specificity, oxidized various polyols (tetritol, pentitol, and hexitol) to corresponding rare ketoses. By a resting cell reaction, 10% of allitol was completely transformed to the product D-psicose, which thus becomes economically feasible for the mass production of D-psicose. Finally, the product was crystallized and confirmed to be D-psicose by analytical methods.