Cues from injured Daphnia and from cyclopoids feeding on Daphnia can modify life histories of conspecifics

Size, age and number of offspring at the first and subsequent tworeproductions were compared in Daphnia treated with cues frominvertebrate predators (adult Cyclopoida fed Daphnia)and from crushed conspecifics. Daphnia in the presence ofinvertebrate predators had earlier maturation, greater size atfirst and subsequent reproductions and a larger number of offspringthan control animals, while the opposite (later maturation andsmaller size at subsequent reproductions) happened when Daphnia were treated with homogenate from crushedconspecifics.     

Effects of genetically modified human skin fibroblasts,stably overexpressing hepatocyte growth factor,on hepatic functions of cocultured C3A cells

Diseases leading to terminal hepatic failure are among the most common causes of death worldwide. Transplant of the whole organ is the only effective method to cure liver failure. Unfortunately, this treatment option is not available universally due to the serious shortage of donors. Thus, alternative methods have been developed that are aimed at prolonging the life of patients, including hepatic cells transplantation and bridging therapy based on hybrid bioartificial liver devices. Parenchymal liver cells are highly differentiated and perform many complex functions, such as detoxification and protein synthesis. Unfortunately, isolated hepatocytes display a rapid decline in viability and liver‐specific functions. A number of methods have been developed to maintain hepatocytes in their highly differentiated state in vitro, amongst them the most promising being 3D growth scaffolds and decellularized tissues or coculture with other cell types required for the heterotypic cell‐cell interactions. Here we present a novel approach to the hepatic cells culture based on the feeder layer cells genetically modified using lentiviral vector to stably produce additional amounts of hepatocyte growth factor and show the positive influence of these coculture conditions on the preservation of the hepatic functions of the liver parenchymal cells' model—C3A cells.     

A flow-through amperometric sensor based on dialysis tubing and free enzyme reactors.

A generic flow-through amperometric microenzyme sensor is described, which is based on semi-permeable dialysis tubing carrying the sample to be analyzed. This tubing (300 microm OD) is led through a small cavity, containing the working and reference electrode. By filling this cavity with a few microl of an appropriate enzyme solution, an amperometric enzyme sensor results. As the dialysis tubing is impermeable for large molecular species such as enzymes, this approach does not require any immobilization chemistry, and as a consequence the enzyme is present in its natural free form. Based on this principle, amperometric sensors for lactate, glucose, and glutamate were formed by filling cavities, precision machined in Perspex, with buffered solutions containing respectively, lactate-, glucose-, and glutamate-oxidase. All sensors showed a large linear range (0-35 mM for glucose, 0-3 mM for lactate, and 0-5 mM for glutamate) covering the complete physiological range. The lower detection limit was in the order of 15-50 microM. Applicability in flow injection analysis systems is demonstrated.     

Summer diapause in Daphnia as a reaction to the presence of fish

A chemical signal, released by a fish predator under summer-likehigh water temperature and long-day photoperiod, caused theformation of resting eggs in a clone of Daphnia magna. No ephippialfemales were recorded and no ephippia were released in the controltreatment during 45 days of the experiment. When exposed tofish water, the fraction of ephippial females reached a maximumof 3.7%, a value comparable to that registered in summer inthe GroBer Binnensee (Northern Germany), a hypertrophic lakeinhabited by fish, which was the source lake for our experimentalclone. The number of ephippia released within 45 days was onaverage 34 ± 22. Ephippia formation could not resultfrom the between-treatment differences in population density,and related patterns of food depletion, since no substantialdifference between control and fish treatment was observed.Instead, specific information on the presence of a predatorprovided a cue which induced the formation of resting eggs inDaphnia. Under heavy predation and very low survival probabilityof parthenogenetic females, ephippia formation in summer canbe adaptive, i.e. higher fitness can be achieved through survivalin the diapausing state than through the immediate reproductivegain via parthenogenesis.     

The lack of vertical migration in Daphnia: the effect of homogenously distributed food

Neither Daphnia hyalina, Daphnia cristata, nor Daphnia cucullata vertically migrated in Lake Mikoajskie and Lake Majcz. We suggest that even under strong fish predation pressure there is no reason to migrate when seston is relatively homogenously distributed throughout the water column.     

Cell hydrophobicity of <Emphasis Type="Italic">Pseudomonas</Emphasis> spp. and <Emphasis Type="Italic">Bacillus</Emphasis> spp. bacteria and hydrocarbon biodegradation in the presence of Quillaya saponin

Biodegradation and hydrophobicity of Pseudomonas spp. and Bacillus spp. strains were tested at different concentrations of the biosurfactant Quillaya saponin. A model mixture of hydrocarbon (dodecane and hexadecane) was used for estimating the influence of surfactants on biodegradation. The bacterial adhesion to hydrocarbon method for determination of bacterial cell surface hydrophobicity was exploited. Among the tested bacterial strains the higher hydrophobicity was noticed for Pseudomonas aeruginosa TK. The hydrophobicity of this strain was 84%. The highest hydrocarbon biodegradation was observed for P. aeruginosa TK (49%) and Bacillus subtilis (35%) strains after 7 days of experiments. Generally the addition of Quillaya saponin increased hydrocarbon biodegradation remarkably. The optimal concentration proved to be 80 mg l⁻¹. The degree of hydrocarbon biodegradation was 75% for P. aeruginosa TK after the addition of saponin. However the most significant increase in biodegradation after addition of Quillaya saponin was in the case of P. aeruginosa 25 and Pseudomonas putida (the increase of biodegradation from 21 to 52% and from 31 to 66%, respectively). It is worth mentioning that decrease of hydrophobicity is correlated with the best biodegradation by P. aeruginosa strain. For the remaining strains, no significant hydrophobicity changes in relation to the system without surfactant were noticed.     

Anti-predator Defence in Three Daphnia Species

Over a two-year period, each of the three Daphnia species in two lakes with different pressure by fish and invertebrate predators exhibited different defensive reactions: predator avoidance in space (Daphnia hyalina), seasonal morphological changes (Daphnia cucullata), and a combination of both (Daphnia cristata). Body size and general susceptibility to predation, combined with predators' preferences were most likely responsible for the kind of defence in each of the three Daphnia.     

Yeast and bacteria cell hydrophobicity and hydrocarbon biodegradation in the presence of natural surfactants: rhamnolipides and saponins

This study concerns the relation between hydrocarbon biodegradation in the presence of natural surfactants and cell hydrophobicity resulting from the use of these surfactants. The relative capabilities of two bacterial strains (Pseudomonas aeruginosa and Bacillus subtilis) and two yeast strains (Candida maltosa, Yarrowia lipolytica) were investigated. The selected microorganisms were tested separately and in combination in order to achieve the optimal degrading performance. The surface cell hydrophobicity of microorganisms and the degree of hydrocarbon biodegradation were measured. The microbial adhesion to the hydrocarbon (MATH) test was used to denote the surface cell hydrophobicity of the microbial species. The results indicate the correlation between the modification of the surface cell and the degree of hydrocarbon biodegradation; however results for bacteria differ from that obtained for yeast strains. Saponins, as the surfactant, was more effective than rhamnolipides during hydrocarbon biodegradation, though the concentration of this surfactant has no significant influence on the surface cell hydrophobicity.     

Food and predation as major factors limiting two natural populations of Daphnia cucullata Sars

A detailed analysis of two euplanktonic populations carried out in the same period, 18 May–11 August, 1978, in two neighboring Mazurian lakes revealed different patterns of changes in population densities and significant differences in fecundity, age structure and mean sizes of individuals despite similar epilimnion temperatures in the lakes. Similar densities were maintained in both populations although food limitation was less important and predation more intense in one than in the other of the two lakes. The relative importance of food limitation and predation is discussed in lakes of low and high fertility. It is also suggested that both low food concentration and high selective predation pressure favors small clutch sizes in cladocerans.     

Cyclomorphosis in Daphnia: an adaptation to avoid invertebrate predation

Seasonal morphological changes in three Daphnia species were followed over a two-year period in two lakes that differ in invertebrate and fish pressure. Whereas the morphology of D. hyalina, the biggest of the three species, varied little from season to season, D. cucullata, the smallest, exhibited the most pronounced seasonal changes in head height/carapace length ratio. The pattern of seasonal changes of body proportions was similar in all size classes and isometric growth of the head was reported for D. cucullata. Unlike the head, tail spine length/carapace length ratio almost did not vary seasonally. Strong negative allometry of tail spine growth was observed. These results are consistent with the hypothesis that helmets and tail spines provide protection against invertebrates in the two smallest, thus most endangered species.