A numerical classification of yeasts of the genusPichia hansen by a factor analysis method

A method of factor analysis was used to establish the relationships between 30 species of a group of yeasts namedPichia on the basis of factors (groups of characters) of decreasing importance.associated to the C.N.R.S. (Centre National de la Recherche Scientifique).     

Characteristics delimiting the genusPichia Hansen

It is confirmed that asci with more than four spores are formed by strains ofPichia membranaefaciens, P. pseudopolymorpha andP. terricola. In view of this it is suggested that the diagnosis of the genusPichia should be amended. Tomato extract proved a more favourable medium for pellicle formation than malt extract.     

A proposal for the structuring of water

In spite of much work, many of the properties of water remain puzzling. A fluctuating network of water molecules, with localised icosahedral symmetry, is proposed to exist derived from clusters containing, if complete, 280 fully hydrogen-bonded molecules. These are formed by the regular arrangement of identical units of 14 water molecules that can tessellate locally, by changing centres, in three-dimensions and interconvert between lower and higher density forms. The structure allows explanation of many of the anomalous properties of water including its temperature-density and pressure-viscosity behaviour, the radial distribution pattern, the presence of both pentamers and hexamers, the change in properties and 'two-state' model on supercooling and the solvation properties of ions, hydrophobic molecules, carbohydrates and macromolecules. The model described here offers a structure on to which large molecules can be mapped in order to offer insights into their interactions.     

On the use of hansen frequencies for estimating rates of behavior

When the occurrence of a behavior is governed by aPoisson process over time, then the mean rate of behavior can be estimated usingHansen frequencies, which record whether the behavior has occurred at least once or not at all in each of several time periods. Here this estimate of the mean rate of behavior, based onHansen frequencies, is compared with the usual estimate, and its properties as an estimate of the mean rate of behavior are discussed in cases where the behavior is not governed by aPoisson process.This research was supported in part by Navy Grant N00014-67-A-0285-0009 to the Department of Statistics, University of Chicago, and by a grant from the Alfred P. Sloan Foundation to the Department of Theoretical Biology.     

A proposal for revision of the quality factor

As a result of recent radiobiological research it has become evident that the RBE of neurons can at low absorbed doses reach values that are substantially higher than the values of the quality factor (Q) currently adopted for radiation protection. There is theoretical and observational evidence that such high RBE values are the rule rather than the exception and that they apply to at least one radiation effect on humans. New values as well as different formulations are proposed for the factor that is employed in radiation protection to weight absorbed doses for their biological effectiveness.     

Genomic studies on killer yeasts belonging to the genusPichia

Twenty-four species belonging to the genusPichia were investigated using restriction fragment length polymorphism (RFLP) and Southern blot hybridization of their genomic DNA.Saccharomyces cerevisiae, Kluyveromyces lactis, Williopsis mrakii andCandida albicans were also included in this study. The RFLP patterns were obtained from digestion of yeast DNA with several restriction endonuclease enzymes, and showed various bands with different mobility; in most isolates, the more deeply stained bands were species-specific. This observation was confirmed by the results obtained from Southern blot hybridization of theEcoRI andXhoI RFLP patterns withP. anomala UCSC 25F DNA, digested with the same enzymes, used as probes. These bands are likely to be ribosomal DNA as shown by hybridization of digested DNA from unrelated yeast species (S. cerevisiae, K. lactis andC. albicans). However, one hybridized band, located at 3.9–4.1 Kb, seems to be peculiar to thePichia species. Our study confirms the usefulness of molecular tools in studying genetic relatedness among yeasts.     

A proposal for the mechanism of carbonic anhydrase action

A new catalytic mechanism is proposed for the hydration of CO₂ by the zinc metalloenzyme carbonic anhydrase. This mechanism identifies the group controlling catalytic activity as an active site histidine, in which the protonated imidazole ring coordinates to zinc, losing a proton. Geometric constraints on the histidine unit make the metal-ligand bond a strained and, therefore, labile one. In the hydration reaction, the metal-bound neutral histidine moiety serves as a proton acceptor for the transient ionization of metal-bound water. Zinc-bound hydroxide attacks the carbon of the substrate to generate metal-bound bicarbonate, and the system regenerates itself by losing the elements of carbonic acid.     

A proposal for modification of the Belgian biotic index method

Modifications to a standard biological water quality assessment method, used in Belgium since 1979, were studied.As a result, we recommend the following:- samples should be processed live- samples should not be washed through a series of sieves- systematic units represented by only one individual should be included in the calculation of the biotic index.Using this modification, the biotic index can be calculated more rapidly and shows a higher correlation with a chemical water quality assessment index.     

A proposal for the classification and evaluation of fall detectors

Falls affect, each year, tens of million of elderly people throughout the world. It can have immediate lethal consequences but also causes many disabling fractures and dramatic psychological consequences which reduce the independence of the person. Falls in the elderly is thus a major public health problem. The “early” detection of fall consequently raises the interest of searchers, as most of elderly fallers cannot return to a standing position on their own following a fall. It is also an interesting scientific problem because it is an ill-defined process. The goals of this study were to classify various approaches used to detect the fall and to point out the difficulty to compare the results of these studies, as there is currently no common evaluation benchmark.     

A proposal for the conservation of the family Cucurbitaceae in Mexico

The pantropical Cucurbitaceae is one of the most important families ofvascular plants. The family includes 118 genera and 825 species, and Mexicois one of its most important centers of diversity, with 34 genera and 141species and subspecific taxa, including 13 cultivated ones. Five genera and 70taxa are endemic to the country. Some Mexican and Latin American wild speciesare close relatives of important crops, and others are employed as food ormedicine. Accordingly, in countries like Mexico the conservation of members ofthis family should be a priority. In this paper a list of members ofCucurbitaceae occurring in Mexico and their distribution patterns at state levelare discussed. Using cluster strategies, the states were classified according totheir floristic similarities. Hotspots of total diversity and endemismsat state level are identified, in order to discuss their role in futureconservation strategies. Iterative methods applied by conservation biology todetermine the best places for conservation are used to identify hierarchicallythe most important states that merit to be considered in this goal. Resultsindicate that implementing conservation strategies in half of the states wouldallow the protection of all the diversity found in the country, especially theendemisms. The combination of the results provided by the different methods isalso discussed as a possibly more efficient way to propose conservationstrategies for important species of the family.     

Differential toxinogenesis in the genusPichia detected by an anti-yeast killer toxin monoclonal antibody

The differential toxinogenesis of 25 isolates belonging to species of the potential yeast killer genusPichia that were previously classified in the genusHansenula was comparatively demonstrated by two serologic techniques (indirect immunofluorescence and double immunodiffusion) by using a monoclonal antibody against a yeast killer toxin produced by a selected strain ofPichia anomala (UCSC 25F). The killer phenotypes of thePichia isolates were evaluated by their ability to kill each other. The results, although of insufficient taxonomic value for a reliable separation of either species or genera, attest to the genomic heterogeneity for the killer character in the genusPichia as well as the presumptive dual killer/sensitive identity for each single isolate.