Complexation between oppositely charged polyelectrolytes: beyond the Random Phase Approximation

We consider the phase behavior of polymeric systems by calculating the structure factors beyond the Random Phase Approximation. The effect of this correction to the mean-field RPA structure factor is shown to be important in the case of coulombic systems. Two examples are given: simple electrolytes and mixtures of incompatible oppositely charged polyelectrolytes. In this last case, all former studies predicted an enhancement of compatibility for increasing charge densities; we also describe the complexation transition between the polyelectrolytes. We determine a phase diagram of the polyelectrolyte mixture that includes both complexation and incompatibility.Comment: 18 pages, 4 figures. Submitted to EPJ-

KNR4, a suppressor of Saccharomyces cerevisiae cwh mutants, is involved in the transcriptional control of chitin synthase genes

The KNR4 gene, originally isolated by complementation of a K9 killer-toxinresistant mutant displaying reduced levels of both 1,3-b-glucan and 1,3-bglucan synthase activity, was recloned from a YCp50 genomic library as a suppressor of Saccharomyces cerevisiae calcofluor-white-hypersensitive (cwh) mutants. In these mutants, which were characterized by increased chitin levels, the suppressor effect of KNR4 resulted, for some of them, in a lowering of polymer content to close to wild-type level, with no effect on the contents of b-glucan and mannan. In all cases, this effect was accompanied by a strong reduction in mRNA levels corresponding to CHS1, CHS2 and CHS3, encoding chitin synthases, without affecting expression of FKS1 and RHO1, two genes encoding the catalytic subunit and a regulatory component of 1,3-b-glucan synthase, respectively. Overexpression of KNR4 also inhibited expression of CHS genes in wild-type strains and in two other cwh mutants, whose sensitivity to calcofluor white was not suppressed by this gene. The physiological relevance of the KNR4 transcriptional effect was addressed in two different ways. In a wild-type strain exposed to a-factor, overexpression of this gene inhibited CHS1 induction and delayed shmoo formation, two events which are triggered in response to the pheromone, whereas it did not affect bud formation and cell growth in a chs1 chs2 double mutant. A chimeric protein made by fusing green fluorescent protein to the C terminus of Knr4p which fully complemented a knr4D mutation was found to localize in patches at presumptive bud sites in unbudded cells and at the incipient bud site during bud emergence. Taken together, these results demonstrate that KNR4 has a regulatory role in chitin deposition and in cell wall assembly. A mechanism by which this gene affects expression of CHS genes is proposed

Consensus report: E. coli O104:H4 (HUSEC041) and the potential threat to European water supplies.

Among the 3rd Seminar for PhD students working on Water and Health which was held in Cannes on 27–29 June 2011, experts from a number of universities and research institutes took the opportunity to discuss the emergence of Escherichia coli O104:H4 in Europe. Especially, possible threats for European water suppliers were considered. The consensus is summarized in this report. The main conclusion was that E. coli O104:H4 would not pose a substantial risk to well managed water supplies, especially where regular monitoring of indicator E. coli is negative. However, this may not apply for small and very small water systems which are quite common in Europe. New strategies like the Water Safety Plan approach are needed to protect also small scale drinking water systems and private wells in Europe. Water used in the processing of foods likely to be eaten raw, especially sprouts, should be of drinking water quality