Critical conditions for ferric chloride-induced flocculation of freshwater algae

The effects of algae concentration, ferric chloride dose, and pH on the flocculation efficiency of the freshwater algae Chlorella zofingiensis can be understood by considering the nature of the electrostatic charges on the algae and precipitate surfaces. Two critical conditions are identified which, when met, result in flocculation efficiencies in excess of 90% for freshwater algae. First, a minimum concentration of ferric chloride is required to overcome the electrostatic stabilization of the algae and promote bridging of algae cells by hydroxide precipitates. At low algae concentrations, the minimum amount of ferric chloride required increases linearly with algae concentration, characteristic of flocculation primarily through electrostatic bridging by hydroxide precipitates. At higher algae concentrations, the minimum required concentration of ferric chloride for flocculation is independent of algae concentration, suggesting a change in the primary flocculation mechanism from bridging to sweep flocculation. Second, the algae must have a negative surface charge. Experiments and surface complexation modeling show that the surface charge of C. zofingiensis is negative above a pH of 4.0 ± 0.3 which agrees well with the minimum pH required for effective flocculation. These critical flocculation criteria can be extended to other freshwater algae to design effective flocculation systems.     

An investigation of habitat occupancy by the nightingale Luscinia megarhynchos with respect to population change at the edge of its range in England

The nightingale Luscinia megarhynchos has undergone population decline and range contraction at the north-western limit of its distribution in England during the last 25 years. We examine patterns of habitat occupancy and habitat availability across sites with a range of population histories to see whether habitat loss is a plausible explanation for these declines. The number of singing males in 1999 correlated with area of primary nightingale habitat in the East Midlands (where the species has declined), but not in East Anglia (where the population has been stable). Change in population size between 1980 and 1999 and current habitat availability were weakly correlated in the East Midlands but not in East Anglia. These results are consistent with habitat loss having contributed to the decline of the nightingale in the East Midlands, but suggest that other, wider-scale, factors may be at least partially responsible for determining the abundance of the species within England as a whole.     

RNA viruses: emerging vectors for vaccination and gene therapy

The application of modern molecular techniques has profoundly influenced our understanding of virus function. As a consequence, virus biology is being directly applied to medical research. It is a reflection of the current pace of virology that we are now beginning to think of our ancient foes as useful and beneficial tools.     

Stoichiometry of the reaction between horseradish peroxidase and p-cresol.

Over a wide range of pH horseradish peroxidase compound I can be reduced quantitatively via compound II to the native enzyme by only 1 molar equivalent of p-cresol. Since 2 molar equivalents of electrons are required for the single turnover of the enzymatic cycle, p-cresol behaves as a 2-electron reductant. With p-cresol and compound I in a 1:1 ratio compound II and p-methylphenoxy radicals are obtained in the transient state. Compound II is then reduced to the native enzyme. A possible explanation for the facile reduction of compound II involves reaction with the dimerization product of these radicals, 1/2 molar equivalent of 2,2'-dihydroxy-5,5'-dimethylbiphenyl. If only 1/2 molar equivalent of p-cresol is present, than at high pH the reduction stops at compound II. The major steady state peroxidase oxidation product of p-cresol (with p-cresol in large excess compared to the enzyme concentration) is Pummerer's ketone. Pummerer's ketone is only reactive at pH values greater than about 9 where significant amounts of the enol can be formed via the enolate anion. Therefore, in alkaline solution it is reactive with compound I, but not with compound II, which is converted into an unreactive basic form. These results indicate that Pummerer's ketone cannot be the intermediate free radical product responsible for reducing compound II in the single turnover experiments. It is postulated that Pummerer's ketone is formed only in the steady state by the reaction of the p-methylphenoxy radical with excess p-cresol.     

Effects on heather of heavy grazing by mountain hares

Continual heavy grazing of small patches of heather by mountain hares produces conspicuous, short, lawn-like bushes. Their probable development is described. The shoots of such heather bushes maintained a juvenile appearance, contained more nitrogen and phosphorus than the surrounding heather and, to judge from their chemical composition, were more digestible. The generalization that tree and shrub twigs of juvenile growth form are more unpalatable to hares than twigs of mature growth form did not apply in this case.     

The DNA-content (Feulgen) of nuclei during mitosis in a root tip of onion

Summary The microphotometric two-wavelength method is demonstrated to permit, even with only an improvised optical set-up, DNA-measurements which would not be possible, at any rate not with a comparable accuracy, with the conventional method.The data, in agreement with earlier results, show that the largest interphase nuclei in the root meristem have already completed their DNA-synthesis.The mean DNA-contents per set of chromatids at late interphase, prophase, and telophase, appeared to be virtually identical. A natural variation in DNA-content, if any, between individual nuclei at these stage would have a coefficient of variation of significantly less, and most likely much less, than 7.3%. The data from metaphase to middle anaphase are, for technical reasons, not yet conclusive. An indicated, moderate, excess of Feulgen-dye in these as compared with earlier and later stages may not be real.The results are fully compatible with a working hypothesis of strict constancy of the DNA-content per chromatid and of its precise doubling during DNA-synthesis (for necessary qualifications see the discussion). It is pointed out that apparently contradictory results by certain other authors do not, for methodological reasons, yet establish disproof of this hypothesis.Contribution from the Program in Cytology, Department of Botany, University of Wisconsin, Madison, supported in part by grants to Dr.C. Leonard Huskins from the Rockefeller Foundation, the American Cancer Society, and the Research Committee of the Graduate School with funds supplied by the Wisconsin Alumni Research Foundation.supported in part by the U. S. Public Health Service and the Wallace C. and Clara A. Abbott Memorial Fund.