CONDITIONS OF ILLUMINATION AND ZOOSPOROGENESIS IN KLEBSORMIDIUM FLACCIDUM1

The filamentous green alga Klebsormidium flaccidum will produce zoospores when cultured on a diurnal regime of 8-hr light and 16-hr dark. Zoosporogenesis is inhibited by interruption of the dark period with light of sufficient intensity and duration. The relationship between intensity and maximum time of interruption before total inhibition of zoosporogenesis is nonlinear.     

Glucose as a substrate in recombinant strain fermentation technology

Summary Glucose supplements to complex growth media of Escherichia coli affect the production of a recombinant model protein under the control of a temperature-sensitive expression system. The bacterial Crabtree effect, which occurs in the presence of glucose under aerobic conditions, not only represses the formation of citric acid cycle enzymes, but also represses the formation of the plasmid-encoded product even though the synthesis of this protein is under the control of the temperature-inducible lambda P _R-promoter/cl857-repressor expression system. When the recombinant E. coli is grown at a moderate temperature (35° C) with protein hydrolysate and glucose as substrates, a biphasic growth and production pattern is observed. In the first phase, the cells grow with a high specific growth rate, utilizing glucose and forming glutamate as a byproduct. The intracellular level of recombinant protein is very low in this phase. Later, glutamate is consumed, indicating an active citric acid cycle. The degradation of glutamate is accompanied by the intracellular accumulation of high amounts of recombinant protein.     

Influence of ethanol on the activities of 3-hydroxy-3-methylglutaryl-coenzyme A-reductase and squalene-hopene-cyclase in Zymomonas mobilis

Summary The influence of different primary aliphatic alcohols on the activities of two key enzymes in hopanoid biosynthesis of Zymomonas mobilis was investigated. By use of ¹⁴C- and ³H-labelled substrates the enzymes 3-hydroxy-3-methylglutaryl-CoA-reductase and squalene-hopenecyclase were detected with activities of 1.6 pmol x (min x mg protein)^-1 and 2.3 pmol x- (min x mg protein)^-1, respectively. Cells grown in the presence of 6% (v/v) ethanol did not show higher activities of these enzymes than cells grown in the presence of 1% (v/v) ethanol. Furthermore, 3-hydroxy-3-methylglutaryl-CoA-reductase was not activated by ethanol. However, ethanol activated the squalene-hopene-cyclase when added to the enzyme test system. Besides ethanol, propanol also had a positive effect on the squalene-hopene-cyclase: the enzyme's activity increased 1.7-fold in the presence of either alcohol at a concentration of 6% (v/v). This corresponded with a similar increase of hopanoid content of whole cells when grown in the presence of 6% (v/v) added ethanol or propanol. These results indicated that the squalene-hopene-cyclase has a regulatory function in the alcohol dependent hopanoid biosynthesis of Z. mobilis.Abbreviation HMG-CoA-reductase 3-hydroxy-3-methylglutaryl-coenzyme A-reductase     

Protease activity and proteolytic modification of cellulases from a Trichoderma reesei QM 9414 selectant

Summary The secretion of multiple forms of cellulolytic enzymes by a Trichoderma reesei QM 9414 selectant exhibiting high protease activity (T. reesei QM 9414/A 30) was investigated using monoclonal, domain-specific antibodies against cellobiohydrolase (CBH) I, CBH II and -glucosidase, and a polyclonal antibody against endoglucanase I. The pattern of appearance of these proteins was followed during growth of the fungus on Avicel cellulose, using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE)/Western blotting/immunostaining. Evidence was obtained that, at late cultivation stages, CBH I and II became partially modified to lower molecular weight components, whereas -glucosidase and endoglucanase I appeared to remain largely intact. Modification of CBH I appeared to commence from the carboxy-terminal AB region, whereas CBH II appeared to become modified both from the amino- (ABB') and the carboxy-terminal. Evidence for a protease activity that modifies the already truncated cellobiohydrolases in the culture filtrate was obtained. These results show that proteolysis at late culture stages may contribute to the multiplicity of cellulases found in T. reesei culture fluids. Initial proteolytic cleavage of CBH I and II may, however, involve an unusual protease not detectable by the azocasein method.Offprint requests to: C. P. Kubicek     

Tetracycline production byStreptomyces aureofaciens: the time lag of production

Summary The exact time course of phosphate consumption in a tetracycline production byStreptomyces aureofaciens has been determined. The data have been compared with model simulations according to a model proposed by Votruba et al. (1984). This led to a revision of his equation for the rate of phosphate consumption and to the proposal that phosphate is consumed proportionally to the growth rate. In contradiction to the model simulations it was found that the length of the time lag of the production is independent of the initial phosphate concentration. While the model explains the time lag through inhibition of the production by phosphate, the measured data show that there must be another or an additional reason for the lag. Simultaneously with the start of the production the organism changes from an organic substrate to ammonia as nitrogen source.All experiments have been carried out in a bubble column of 651 working volume as fed batch fermentation. An autoanalyzer and a HPLC was coupled to the reactor for automatic measurement of phosphate, ammonia, sucrose and products in short intervals. Composition of the outlet gas, pH, pO₂, temperature and weight of the substrate flasks were monitored on-line.     

Control of bacterial DNA supercoiling

Two DNA topoisomerases control the level of negative supercoiling in bacterial cells. DNA gyrase introduces supercoils, and DNA topoisomerase I prevents supercoiling from reaching unacceptably high levels. Perturbations of supercoiling are corrected by the substrate preferences of these topoisomerases with respect to DNA topology and by changes in expression of the genes encoding the enzymes. However, supercoiling changes when the growth environment is altered in ways that also affect cellular energetics. The ratio of [ATP] to [ADP], to which gyrase is sensitive, may be involved in the response of supercoiling to growth conditions. Inside cells, supercoiling is partitioned into two components, superhelical tension and restrained supercoils. Shifts in superhelical tension elicited by nicking or by salt shock do not rapidly change the level of restrained supercoiling. However, a steady-state change in supercoiling caused by mutation of topA does alter both tension and restrained supercoils. This communication between the two compartments may play a role in the control of supercoiling.     

The Rashomon Effect: When Ethnographers Disagree

Disagreements between ethnographers often arise because of the particular circumstances of field-work or attributes of the ethnographers. A positivist search for truth versus error may be less fruitful than a constructionist examination of the research itself. This article suggests a conceptual framework for such a constructionist approach.     

Effect of a cold stimulus on the synthesis of uncoupling protein in brown adipose tissue of rats and newborn rabbits

Rats are known to respond to a cold stimulus by increasing the activity and amount of the uncoupling protein in brown adipose tissue. A 48 h cold stimulus was found to increase the synthesis of uncoupling protein 3.g-fold in 4–5 week old rats whereas no change was observed with newborn rabbits. The lack of response in the latter case may reflect a difference between rabbits and rats or that synthesis is already maximal in newborn rabbits.     

Mitochondrial DNA of the basidiomycete Polyporus ciliatus

Summary Mitochondrial (mt) DNA of the white rot fungus Polyporus ciliatus was isolated and characterized. As a result of detailed restriction enzyme analysis, a physical map was established showing that this circular DNA has a molecular weight of 88.2 kb. By heterologous cross hybridization the sites of three mt genes were recognized. By nonselective cloning of mt DNA fragments in Saccharomyces cerevisiae, an autonomously replicating sequence (ars) was identified which has potential application in the development of a prokaryotic/eukaryotic shuttle vector.