Rapid enumeration of viable micro-organisms by staining and direct microscopy

A rapid method is described that uses the tetrazolium salt 2-( p -iodophenyl-3-( p -nitrophenyl)-5-phenyl tetrazolium chloride (INT) to stain viable micro-organisms retained on a filter membrane. Good correlation exists between numbers of INT stained cells and aerobic plate counts of single strain cultures of bacteria and yeasts. A pre-treatment step allows the technique to be used for pasteurized milk.     

Behaviour in a population of Columbian ground squirrels, Spermophilus columbianus columbianus

Field observations and films of laboratory encounters were used to describe and quantify behaviour in a population of Columbian ground squirrels. Activity correlated with ambient temperature. Feeding, the most frequent behaviour, decreased during mid-day whereas other behavioural patterns increased. Squirrels nearly always seemed alert, even during other behavioural patterns. Three of seven vocalizations indicated alarm. Possible adult scent-marking nerver exceeded 1 per cent of above-ground activity and decreased seasonally. Juvenile play was frequent; yearling play became more aggressive and was replaced by aggression by mid-season. Adult aggression rarely involved contact; aggression was most frequent during breeding and lactation among males and females, respectively. The behaviour of this population was similar to that observed in other populations of the same and other sciurids. Most differences cannot be explained without ecological investigation of the other populations.     

Adhesion of phospholipid vesicles to Chinese hamster fibroblasts: Role of cell surface proteins

The adhesion of artificially generated lipid membrane vesicles to Chinese hamster V79 fibroblasts in suspension was used as a model system for studying membrane interactions. Below their gel-liquid crystalline phase transition temperature, vesicles comprised of dipalmitoyl lecithin (DPL) or dimyristoyl lecithin (DML) absorbed to the surfaces of EDTA- dissociated cells. These adherent vesicles could not be removed by repeated washings of the treated cells but could be released into the medium by treatment with trypsin. EM autoradiographic studies of cells treated with[(3)H]DML or [(3)H]DPL vesicles showed that most of the radioactive lipids were confined to the cell periphery. Scanning electron microscopy and fluorescence microscopy further confirmed the presence of adherent vesicles at the cell surface. Adhesion of DML or DPL vesicles to EDTA-dissociated cells modified the lactoperoxidase-catalyzed iodination pattern of the cell surface proteins; the inhibition of labeling of two proteins with an approximately 60,000- dalton mol wt was particularly evident. Incubation of cells wit h (3)H-lipid vesicles followed by sodium dodecyl sulfate (SDS)- polyacrylamide gel electrophoresis showed that some of the (3)H-lipid migrated preferentially with these approximately 60,000-mol wt proteins. Studies of the temperature dependence of vesicle uptake and subsequent release by trypsin showed that DML or DPL vesicle adhesion to EDTA- dissociated cells increased with decreasing temperatures. In contrast, cells trypsinized before incubation with vesicles showed practically no temperature dependence of vesicle uptake. These results suggest two pathways for adhesion of lipid vesicles to the cell surface-a temperature-sensitive one involving cell surface proteins, and a temperature-independent one. These findings are discussed in terms of current models for cell-cell interactions.