Diversity of Lactobacillus reuteri Strains in Converting Glycerol into 3-Hydroxypropionic Acid.

The present study aims at comparing the performances of three Lactobacillus reuteri strains (DSM 20016, DSM 17938, and ATCC 53608) in producing 3-hydroxypropionic acid (3-HP) from glycerol and at exploring inhibition phenomena during this bioconversion. Differences were highlighted between the three strains in terms of 3-HP production yield, kinetics of substrate consumption, and metabolite production. With a maximal productivity in non-optimal conditions (free pH) around 2 g.L(-1).h(-1) of 3-HP and 4 g.L(-1).h(-1) of 3-hydroxypropionaldehyde (3-HPA) depending on the strain, this study confirmed the potential of L. reuteri for the biotechnological production of 3-HP. Moreover, the molar ratios of 3-HP to 1,3-propanediol (1,3-PDO) obtained for the three strains (comprised between 1.25 and 1.65) showed systematically a higher 3-HP production. From these results, the DSM 17938 strain appeared to be the most promising strain. The impact of glycerol bioconversion on the bacteria's physiological state (a decrease of around 40 % in DSM 17938 cells showing an enzymatic activity after 3 h) and survival (total loss of cultivability after 2 or 3 h depending on the strains) was revealed and discussed. The effect of each metabolite on L. reuteri DSM 17938 was further investigated, displaying a drastic inhibition caused by 3-HPA, while 3-HP induced lower impact and only at acidic pH.

Influence of polyols on the structural properties of Kluyveromyces lactis beta-galactosidase under high hydrostatic pressure.

The conformational changes in dimeric Kluyveromyces lactis beta-galactosidase induced by hydrostatic pressure were investigated by means of its intrinsic tryptophan fluorescence. At high pressure, the fluorescence emission spectrum was shifted to the red, indicating the exposure of buried Trp residues to the aqueous solvent. This spectral change was paralleled by a loss of enzyme activity. The shift of the emission spectrum was quantified by evaluating the centre of spectral mass ((nu(g))), which is an intensity-weighted mean wavenumber. The experimental data could be fitted to a two-state transition (native<-->denatured), corrected for a linear pressure dependence of (nu(g)), and allowed the determination of thermodynamic parameters deltaG0(app), V(app) and P(1/2). The results were consistent with a partial unfolding of the protein and not simply with dissociation of this dimeric enzyme. In the presence of polyols, the native conformation of beta-galactosidase was considerably more resistant to pressure. This protective effect of polyols is probably due to a reduced accessibility of water inside the protein structure, through the direct or indirect action of these additives on the enzyme.