Thermoregulatory behavior and temperature gradient perception in a juvenile fish (Poecilia reticulata)

The thermoregulatory behavior of guppies in a temperature gradient was studied under conditions offering one degree of locomotor freedom, in which displacement of the fish was coupled to a change of occupied temperature, and two degrees of locomotor freedom, in which the added dimension allowed for thermally neutral movement, thus uncoupling any obligatory link between displacement and temperature change. More animals failed to thermoregulate in the second than in the first geometrical system (32% vs. 7%); however, the means of the temperature preferenda (Tp) were the same in both gradient configurations and the frequency distributions along the temperature axis were indistinguishable. In both geometrical systems, mean swimming speed along the temperature axis showed well-defined minima coinciding with the Tp. It was shown that the mean components of movement with respect to the thermal and thermally neutral axes both showed minima at Tp. Further analyses of the actual behavior confirm that in the vicinity of Tp the movements of the fish show little dependence on direction. The analyses thus suggest that thermoregulatory movements are not adjusted in response to movement-generated directional information derived from the temperature gradient. The primary determinant of thermoregulatory behavior in fish may require a more complex awareness of the thermal arrangement of the environment than can be furnished by the instantaneous perception of the local gradient structure.     

Subclasses of simian-virus-40 large tumor antigen. Partial purification and DNA-binding properties of two subclasses of tumor antigen from productively infected cells

Two major subclasses of simian virus 40 tumor antigen were prepared from productively infected monkey cells. These subclasses can be distinguished by their sedimentation properties: one tumor antigen form sediments at 5-6S and the other at 14-16S. The DNA-binding properties of these subclasses were investigated by two different experimental procedures. In the first procedure, the DNA binding of subclasses of crude tumor antigen, separated by zone velocity sedimentation, were assayed by immunoprecipitation of the DNA-protein complexes. In the second procedure, the two tumor antigen forms were partially purified by column chromatography and DNA binding was tested in a filter binding assay. Both procedures gave comparable results. (a) The 5-6-S and the 14-16-S tumor antigen bound specifically to a DNA restriction fragment containing the viral genome control regions. (b) At low salt concentrations, both subclasses bound to specific and to nonspecific DNA sequences; competition experiments in the presence of nonspecific DNA showed, however, that the affinity of both tumor antigen forms for the viral genome control region was at least 10-fold higher than their affinity for nonspecific DNA sequences. (c) The binding of the 5-6-S subclass to viral control region DNA was optimal at 60-80 mM NaCl while specific DNA binding of the 14-16-S form was optimal at 150-200 mM NaCl; however, binding of the 14-16-S form to nonspecific DNA sequences was also more resistant to high salt concentrations than that of the 5-6S form. (d) Both tumor antigen forms bound well to specific and to nonspecific DNA at pH 6-6.5; with increasing pH values, binding to nonspecific DNA decreased while binding to specific DNA reached an optimum at pH 7-7.5. Binding of the 14-16-S form to viral origin DNA was more resistant to pH values above 7.5 than binding of the 5-6-S form.     

Stability regions in predator-prey systems with constant-rate prey harvesting

Summary We analyze the global behavior of a predator-prey system, modelled by a pair of non-linear ordinary differential equations, under constant-rate prey harvesting. By methods analogous to those used to study predator harvesting, we characterize the theoretically possible structures and transitions. With the aid of a computer simulation we construct examples to show which of these transitions can be realized in a biologically plausible model.Sponsored by the United States Army under Contract No. DAAG29-75-C-0024 and the National Research Council of Canada, Grant No. 67-3138.     

Growth of fungi and bacteria in the reciprocating jet bioreactor

In a comprehensive study the properties of the reciprocating-jet-bioreactor have been investigated. Fermentations have been carried out with two fungi and one bacterium. The fungi were Cyathus striatus for the production of antibiotics and Aspergillus niger for the production of citric acid. The bacterium Zymomonas mobilis was used in an anaerobic fermentation for the production of ethanol. The reciprocating-jet-bioreactor showed excellent properties as fermenter, especially when the biosuspension is highly viscous and non-Newtonian by nature.Lecture held on the occasion of the Third Joint Schlesinger Seminar at the Institute of Technology of the Technion-Haifa, May, 8–9th, 1990     

Investigations of phagocytosis concerning the immunological defence mechanism of Mytilus edulis using a sublethal luminescent bacterial assay (Photobacterium phosphoreum).

1. A simple method for the determination of phagocytosis activity using mussel hemocytes by measuring the bioluminescence is presented. 2. The immunological defence activity based on phagocytosis is measured and quantified by a luminescent bacterial assay with Photobacterium phosphoreum. 3. The measuring system allows us to establish the stress of the immunological defence mechanism of organisms exposed to chemicals and polluted rivers or sewage. Results with reference substances and the phagocytosis indices of exposed mussels from Norwegian aquaculture plants compared to those of mussels from the German Wadden Sea are given as examples.