Simultaneous enzyme production, Levan-type FOS synthesis and sugar by-products elimination using a recombinant Pichia pastoris strain expressing a levansucrase-endolevanase fusion enzyme

BACKGROUND

Although Levan-type fructooligosaccharides (L-FOS) have been shown to exhibit prebiotic properties, no efficient methods for their large-scale production have been proposed. One alternative relies on the simultaneous levan synthesis from sucrose, followed by endolevanase hydrolysis. For this purpose, several options have been described, particularly through the synthesis of the corresponding enzymes in recombinant Escherichia coli. Major drawbacks still consist in the requirement of GRAS microorganisms for enzyme production, but mainly, the elimination of glucose and fructose, the reaction by-products.

RESULTS

The expression of a fusion enzyme between Bacillus licheniformis endolevanase (LevB1) and B. subtilis levansucrase (SacB) in Pichia pastoris cultures, coupled with the simultaneous synthesis of L-FOS from sucrose and the elimination of the residual monosaccharides, in a single one-pot process was developed. The proof of concept at 250 mL flask-level, resulted in 8.62 g of monosaccharide-free L-FOS and 12.83 gDCW of biomass, after 3 successive sucrose additions (30 g in total), that is a 28.7% yield (w L-FOS/w sucrose) over a period of 288 h. At a 1.5 L bioreactor-level, growth considerably increased and, after 59 h and two sucrose additions, 72.9 g of monosaccharide-free L-FOS and 22.77 gDCW of biomass were obtained from a total of 160 g of sucrose fed, corresponding to a 45.5% yield (w L-FOS/w sucrose), 1.6 higher than the flask system. The L-FOS obtained at flask-level had a DP lower than 20 fructose units, while at bioreactor-level smaller oligosaccharides were obtained, with a DP lower than 10, as a consequence of the lower endolevanase activity in the flask-level.

CONCLUSION

We demonstrate here in a novel system, that P. pastoris cultures can simultaneously be used as comprehensive system to produce the enzyme and the enzymatic L-FOS synthesis with growth sustained by sucrose by-products. This system may be now the center of an optimization strategy for an efficient production of glucose and fructose free L-FOS, to make them available for their application as prebiotics. Besides, P. pastoris biomass also constitutes an interesting source of unicellular protein.

[Attention and the executive functions]

AIMS

The objective of this study was to determine the relations that exist between attention and the executive functions, and between attention deficit hyperactivity disorder (ADHD) and dysexecutive syndrome, while at the same offering a definition of these terms. To achieve this, several aspects related to attention and the executive functions are reviewed, including the evolution of the concept, the different types and the anatomical location.

DEVELOPMENT

The analysis investigates the possible relations between attention and the executive functions, and the modifications that have taken place in ADHD over time, which leads us to consider whether it is the children themselves and the factors that may have influenced these differences. The work then moves on to analyse the possible explanation behind the most frequent symptoms: attention deficit, hyperactivity and impulsiveness, and more especially whether they can be symptoms of executive dysfunction. The possibility of several clinical forms then arises. Finally, we accept the possible cause as being due to an alteration in neurotransmitters, especially dopamine and noradrenalin. A discussion is also included on whether the new interpretation, executive dysfunction, entails a different treatment and whether this offers some benefit for the child.

CONCLUSIONS

Attention is related to the executive functions, but it is not one of them. ADHD has several clinical forms, one of which (although not the only one) may be dysexecutive syndrome. The clinical symptoms may be caused by a delay in the development of distinct neurotransmitter systems.

[Superior vena cava compression syndrome. Apropos of 69 cases]

Sixty-nine patients with a superior vena cava syndrome were treated by radiotherapy. Forty were also given chemotherapy before or after irradiation. Twenty-nine had bronchial carcinoma, thirteen had other solid tumors, fourteen had lymphosarcoma and thirteen had no histological diagnosis. Subjective improvement was recorded in 86% of cases and the objective response rate was 41%. The response was obtained in a mean period of 4 weeks and its duration was 39 weeks for lymphosarcomas and only 6 weeks for solid tumors. Overall 1 year survival was 18%. Poor results obtained in superior vena cava syndrome incites recommendation of more intensive radiochemotherapeutic management.