Recombinant cellobiose dehydrogenase from Thermothelomyces thermophilus: Its functional characterization and applicability in cellobionic acid production.

The fungus Thermothelomyces thermophilus is a thermotolerant microorganism that has been explored as a reservoir for enzymes (hydrolytic enzymes and oxidoreductases). The functional analysis of a recombinant cellobiose dehydrogenase (MtCDHB) from T. thermophilus demonstrated a thermophilic behavior, an optimal pH in alkaline conditions for inter-domain electron transfer, and catalytic activity on cellooligosaccharides with different degree of polymerization. Its applicability was evaluated to the sustainable production of cellobionic acid (CBA), a potential pharmaceutical and cosmetic ingredient rarely commercialized. Dissolving pulp was used as a disaccharide source for MtCDHB. Initially, recombinant exoglucanases (MtCBHI and MtCBHII) from T. thermophilus hydrolyzed the dissolving pulp, resulting in 87% cellobiose yield, which was subsequently converted into CBA by MtCDHB, achieving a 66% CBA yield after 24 h. These findings highlight the potential of MtCDHB as a novel approach to obtaining CBA through the bioconversion of a plant-based source.

Phosphate-solubilization mechanism and in vitro plant growth promotion activity mediated by Pantoea eucalypti isolated from Lotus tenuis rhizosphere in the Salado River Basin (Argentina).

AIMS: To isolate and characterize phosphate-solubilizing strains from a constrained environment such as the Salado River Basin and to assess their phosphate-solubilizing mechanisms, to further selection of the most promising strains to inoculate and improve the implantation and persistence of Lotus tenuis in the most important area devoted to meat-cow production in Argentina. METHODS AND RESULTS: Fifty isolates were obtained and through BOX-PCR analysis, 17 non-redundant strains were identified. Subsequently, they were found to be related to Pantoea, Erwinia, Pseudomonas, Rhizobium and Enterobacter genera, via 16S rRNA gene sequence analysis. This was in agreement with the clusters obtained by antibiotic resistance analysis. All isolates were tested for their phosphate-solubilizing activity and selected strains were inoculated onto L. tenuis plants. The most efficient isolate, was identified as Pantoea eucalypti, a novel species in terms of plant growth-promoting rhizobacteria. CONCLUSIONS: The isolates obtained in this study showed a significant in vitro plant-growth promoting activity onto Lotus tenuis and the best of them solubilizes phosphate mainly via induction of the metabolism through secretion and oxidation of gluconic acid. SIGNIFICANCE AND IMPACT OF THE STUDY: The use of these bacteria as bioinoculants, alone or in combination with nitrogen-fixing micro-organisms, could be a sustainable practice to facilitate the nutrient supply to Lotus tenuis plants and preventing negative side-effects such as eutrophication.

Purification and general properties of L-fucose dehydrogenase from Pullularia pullalans

An inducible L-fucose dehydrogenase from the yeast-like fungus Pullularia pullulans was purified and studied. The enzyme catalyses the oxidation of L-fucose to L-fuconic acid possibly throught its unstable L-funcono-lactone. the enzyme was purified to hemogeneity by a sequence of protamine sulfate treatment, ammonium sulfate fractionation, gel filtration on Sephadex G-100, and DEAE-cellulose chromatography. This sequence resulted in an 87 fold purification. The apparent molecular weight determined by gel filtration and SDS polyacrilamide gel electrophoresis was 40 000. the dehydrogenase was NAD-especific and showed a high sugar substrate specificity. Of several D-and L-aldoses tested only L-fucose, L-galactose and-arabinose served as substrates. The maximum velocity for the reaction was at 33- and pH 10.5. Under these conditions, the Km values, and D-arabinose, respectively. The enzyme was strongly inhibited by thiol reagents, heavy metal ions, and was not particularly stable. At 4- it rapidly los activity, but remained active for two months when maintained at -20-. The enzyme has been used to quantativate L-fucose

L-arabinose metabolism in Azospirillum brasiliense.

An oxidative pathway by which L-arabinose is converted to alpha-ketoglutarate in crude extracts of Azospirillum brasiliense is demonstrated. Specific activities of enzymes involved in the pathway were determined, and several pathway intermediates were identified.