Biomedical subjects

U Behrens

Publications and source records attributed to U Behrens.

32 records · Page 2Linked to original sources

PubMed1978

Fine structure of the cell surface and Golgi apparatus of Ochromonas.

Ochromonas danica has an unusually flexible cell surface capable of producing projections of varying sizes and shapes: large projections, 340-360 nm long, and small projections, 50-110 nm long. These projections have been demonstrated by transmission and scanning electron microscopy; some of them may break off into the medium and be the source of extracellular membranes and vesicles reported in the cell-free O. danica growth medium. Ruthernium red stained the acid mucopolysaccharide layer just outside the cell surface as well as small blebs at the cell surface. The Golgi complex of O. danica, Ochromonas malhamensis, Ochromonas sociabilis and Ochromonas sp. produced small coated vesicles which may move toward and fuse with the plasma membrane. The role of the several vesicles is unknown but possible functions are discussed.

Animals↗

PubMed1977

[Production of pullulan].

Optimum conditions for the production of pullulan by Pullularia pullulans were elaborated by examinating growth and production with different carbohydrates and mixtures of carbohydrates. With starch hydrolysates or mixtures of starch and simple sugars, p.e. glucose or saccharose, better results were achieved than with simple sugars alone or with starch. Condtions for optimum pullulan production are fast undisturbed growth, mediated by fast utilizable simple sugars like glucose followed by a substantial decreased growth rate in which production occurs, mediated by a sufficient supply of nutrite substances and a slow utilizable carbohydrate like starch.

Culture Media↗

PubMed1977

[Enzymatic examination of citrate-isocitrate accumulation in yeasts].

The activities of the enzymes citrate synthase, aconitate hydratase, isocitrate dehydrogenase and isocitrate lyase in cell homogenates of n-paraffin grown citrate plus isocitrate accumulating yeasts (C. lipolytica high rate accumulating strain and C. guilliermondii low rate accumulating strain) were determined. It is shown that the activities of the enzymes decline after transition from tropho- to idiophase and remain constant with exception of isocitrate lyase which diminishes slowly. The decline in activity of the isocitrate lyase was greatest in the cells of C. guilliermondii. It is discussed that the differences of the enzymatic activities in the tropho- and idiophase, resp. may be artefacts due to changes in the structure of cellular envelope, but that the decline of lyase activity in the idiophase could be one factor determining the rate of citric- and isocitric acid overproduction. The diminishing of isocitrate lyase in the course of idiophase is interpreted as example of a disappearing enzyme no further needed for normal function of the cells.

Aconitate Hydratase↗

PubMed1977

[Production of yeast biomasses from starch].

The well known fodder yeasts do not accumulate extracellular amylolytic enzymes and are therefore unable to utilize starches for the production of microbial biomasses. Some of the Endomycopsis yeasts produce glucoamylase but their specific growth rate is so small that continuous cultivation in starch containing media results in low productivites. In the "Symba-process" this drawback is overcome by a twostage fermentation process. In the first stage only Endomycopsis fibuliger yeasts are continuously cultivated and in the second stage the main part of the starch containing medium is converted to microbial biomasses by a mixed culture consisting of fodder yeasts (p.a. Candida utilis) and Endomycopsis fibuliger transferred continously from the first stage. In this work methods for evaluating conditions of cultivation of such a process are presented and a two stage continuous fermentation of a starch containing medium is performed. In the second stage with a dilution rate of D Y 0,174 h-1 a productivity of 1,7 g dry biomasses/1-h was attained Methods for improving the productivity are discussed.

Amylases↗

PubMed1977

[Nitrogen utilization and xanthan production by Xanthomonas campestris].

In media with mixed nitrogen sources (nitrate plus yeast extract) a three auxic growth is observed. The first growth phase is characterized by preferential utilization of the amino acids of the yeast autolysate and the utilization of only small amounts of nitrate. During the second growth phase nitrate is preferentially utilized. In the third phase there is only growth without dividing of cells and the accumulation of xanthan takes place. The change from growth by dividing to growth without dividing means a change from balanced to unbalanced growth. It is proposed that xanthan production is connected with unbalanced growth.

Amino Acids↗

PubMed1974