Effect of Gel Exposition on Calcium and Carbonate Ions Determines the Stm-l Effect on the Crystal Morphology of Calcium Carbonate.

Biomineralization of fish otoliths is regulated by macromolecules, such as proteins, whose presence is crucial for the functionality and properties of these mineralized structures. Special regulatory effects are exerted by intrinsically disordered proteins, such as the polyanionic Starmaker-like protein from medaka, a homolog of zebrafish Starmaker. In this study, we employed a set of bioinspired mineralization experiments with a single diffusion system to investigate the effect of the Starmaker-like protein on calcium carbonate biominerals with regards to the prior exposition of the protein to calcium or carbonate ions. Interestingly, the bioinspired minerals grown in the presence of the Starmaker-like protein in calcium- or carbonate-type experiments differ significantly in terms of morphology and protein distribution within the crystals. Our deeper analysis shows that the Starmaker-like protein action is a result of the environmental conditions to which it is exposed. These findings may be of special interest in the areas of biomineralization process pathways and biomaterial sciences.

The influence of oxygen limitation for the production of succinic acid with recombinant strains of Yarrowia lipolytica.

The yeast Yarrowia lipolytica is able to produce high amounts of several organic acids such as pyruvic, citric, isocitric, alpha-ketoglutaric, and succinic acid. Here we report on the influence of the reduced activity of succinate dehydrogenase in Y. lipolytica on its ability to produce succinate. The recombinant strains Y. lipolytica H222-AZ1 and H222-AZ2 were created by exchange of the native promoter of the succinate dehydrogenase subunit 2 encoding gene by inducible promoters. During the cultivation of the strain Y. lipolytica H222-AZ1 in shaking flask experiments, it was found that the promoter exchange resulted in an increase in succinic acid (SA) production. Moreover, it was found that the production of SA depends on an additional limitation of oxygen. Fed-batch cultivations in 1-l bioreactors confirmed this fundamental finding. Y. lipolytica H222-AZ1 produced 2 g l(-1) of SA with oxygen supply and 9.2 g l(-1) under the limitation of oxygen after 165 h. By using a less active promoter in Y. lipolytica H222-AZ2, the production of SA was increased to 25 g l(-1) with a productivity of 0.152 g (l*h)(-1) and a selectivity of 67 % after 165 h. Yields of 2.39 g SA per gram biomass and 0.26 g SA per gram glycerol were found.