Accumulation of pyrophosphate and other energy-rich phosphorus compounds under various conditions of yeast growth

In the cells of hybrid yeast strain Saccharomyces N.C.Y.C. 644 SU₃ (Karlsberg collection), a large amount of pyrophosphate (30–300 mol/g of dry weight) accumulates whatever the aeration conditions and the content of glucose in the medium. The content of pyrophosphate is 10–1000 times higher than that of ATP. At the early and mid-exponential growth phases two maxima of pyrophosphate accumulation are observable. The periods of maximal pyrophosphate accumulation in yeast coincide with those of the minimal content of polymeric acid-soluble polyphosphates and intense budding. In the light of the data obtained, the question is discussed as to the relationship between the metabolism of pyrophosphates and acid-soluble polyphosphates in yeast.     

The transient properties of balancing selection in large finite populations

The transient properties of balancing selection in large, but finite, populations are described by means of an asymptotic analysis. Heterotic selection is shown to retard the rate of loss of genetic variation while random environment selection is shown to retard the rate of loss of variation when the initial variant is a rare mutant. Otherwise random environment selection can speed up the loss of variation for certain parametric cases. The asymptotic analysis leads to a particularly simple conceptualization of the selection process which allows the computation of asymptotic forms of the dominant eigenvalue of the process.     

Observations on the immature Chironomidae of a polluted lowland brook-pond system (Antwerp,Belgium), aerated by the Phallus process

A lowland brook-pond system polluted by organic waste was aerated by a new aeration method (Phallus process).The immature chironomids were investigated. Forty-two species or species groups were found.The changes in community composition, species richness, diversity, redundancy, abundance and biomass were studied in the light of the recovery after treatment. Before aeration started, chironomids were absent in the aeration basin. After 81/2 months of aeration a chironomid community characterized by low species richness (four species) and high redundancy was established. Prolonged aeration resulted in a further increase of the species diversity and during the last survey, after about 2 years of aeration, the chironomid species richness had increased to 18 species. Similar trends could be found for the downstream sampling stations. The longitudinal recovery pattern probably restored the original zonation of the chironomid species, resulting from an ecological gradient created by the linear change in physiography of the water body. Orthocladiinae dominated in the brook stretch, whereas Chironominae and to a lesser extent Tanypodinae dominated in the ponds.