Heat inactivation of catalase from Staphylococcus aureus MF-31.

The effects of heat on catalase from Staphylococcus aureus lysates were examined. Catalase activity increased with increasing concentrations of potassium phosphate buffer, when heated at temperatures between 50 and 65 degrees C for 10 min. Inactivation of catalase by NaCl during heating was demonstrated. Extended heating of S. aureus cells at 52 degrees C resulted in a slight decrease in catalase activity of the resultant lysates. This decrease was more pronounced in the presence of salt. Heating at 62 degrees C caused a decrease in catalase activity, but not complete inactivation. These results implicate the combined effects of heat, and NaCl in the inactivation of catalase from S. aureus. The findings are consistent with the hypothesis that H2O2 may accumulate as a result of decreased catalase activity and be responsible for the decreased colony-forming ability of stressed S. aureus.     

Usefulness of the stomacher in a microbiological regulatory laboratory.

The relative efficiency of the Waring blender, the Stomacher 400, and the Stomacher 3500 for preparing food samples for microbiological analysis was studied. Comparative aerobic plate count (APC) values were determined on 671 samples, representing 30 categories of foods. Of the 26 categories of nonfatty foods, the blender gave significantly higher geometric mean APC values than those given by the Stomacher 400 and the Stomacher 3500 in 65 and 69 percent of the categories, respectively. In a comparison of the two Stomacher models, the Stomacher 400 gave significantly higher geometric mean APC values than these given by the Stomacher 3500 in 73 percent of the food categories. Addition of Tween 80 to four categories of fatty foods at concentrations of 0.5, 1.0, and 2.0 percent did not raise the APC values given by either model of stomacher to the levels given by the Waring blender. Overall, the efficiency of both models of Stomacher, relative to the blender and to each other, was specific and depended upon the particular food being analyzed.     

Effects of pH and Oxygen on Photosynthetic Reactions of Intact Chloroplasts

Oxygen inhibition of photosynthesis was studied with intact spinach (Spinacia oleracea L.) chloroplasts which exhibited very high rates of photosynthetic CO₂ reduction and were insensitive to additions of photosynthetic intermediates when CO₂ was available at saturating concentrations. Photosynthetic rates were measured polarographically as O₂ evolution, and the extent of the reduction of substrate was estimated from the amount of O₂ evolved. With CO₂ as substrate, inhibition of photosynthesis by O₂ was dependent on pH. At pH values above 8, rates of O₂ evolution were strongly inhibited by O₂ and only a fraction of the added bicarbonate was reduced before O₂ evolution ceased. The extent of O₂ evolution declined with increasing O₂ concentration and decreasing initial bicarbonate concentration. At pH 7.2, the initial photosynthetic rate was inhibited about 30% at high O₂ levels, but the extent of O₂ evolution was unaffected and most of the added bicarbonate was reduced. Photosynthetic O₂ evolution with 3-phosphoglycerate as substrate was similarly dependent on pH and O₂ concentration. In contrast, there was little effect of O₂ and pH on oxaloacetate-dependent oxygen evolution. Acid-base shift experiments with osmotically shocked chloroplasts showed that ATP formation was not affected by O₂. The results are discussed in terms of a balance between photosynthetic O₂ evolution and O₂ consumption by the ribulose diphosphate oxygenase reaction.     

The chemical nature of osmium tetroxide fixation and staining of membranes by x-ray photoelectron spectroscopy.

X-ray photoelectron spectroscopy was used to determine the oxidation states of osmium compounds present in erythrocyte ghost preparations and related systems treated with osmium tetroxide. Osmium tetroxide and cholesterol, codeposited at -100 degrees C, began to react at -70 degrees C, and Os(VI) was formed. Similarly, Os(VI) was detected for the known cholesterol-osmate ester prepared and purified chemically. However, osmium tetroxide applied in phosphate buffer (pH 7.2) gave rise to large proportions of Os(IV) and Os(III) species in addition to Os(VI) compounds. Egg phosphatidylcholine likewise produced a mixture of Os(VI), Os(IV), and Os(III), but dipalmitoyl phosphatidylcholine failed to give significant amounts of osmium containing products under identical conditions. Glutaraldehyde gave a mixture of compounds with the same osmium oxidation states when allowed to react with aqueous osmium tetroxide. Unfixed and glutaraldehyde-fixed erythrocyte ghosts also produced mixtures of Ss(VI), Os(IV) and Os(III) under conditions identical to those of normal tissue processing. Additionally, the mixture of adducts initially formed by treatment with osmium tetroxide was further reduced by dehydration of the tissue with ethanol, rpesulting in a final mixture which was 50-60% Os(III). The results support a scheme for the reaction os osmium tetroxide with tissues in which the initial reaction site is the double bonds of unsaturated lipids to form Os(VI) derivatives. Subsequent hydrolysis and further reduction yield complexes of Os(IV) and Os(III). A mixture of these three states is present in membrane specimens during microscopic observation. Os(VI) and Os(IV) could be present as osmate esters and osmium dioxide, respectively; Os(III) could be present as an oxo- or amino complex(es). The photoelectron spectrum of intact erythrocyte ghosts can be synthesized from the spectra of phospholipid and cholesterol only, suggesting the predominance of the reaction with lipids in the fixation process.     

An ultrastructural study of pyrenoids inLeptosiropsis torulosa

Summary The ultrastructure of the mature pyrenoid of the chaetophoracean algaLeptosiropsis torulosa is unlike any described for the green algae. The nucleus is surrounded by the pyrenoid, with only the endoplasmic reticulum interrupting the encircling pyrenoid. The pyrenoid possesses only the appressed plastid membranes that are in contact with the nucleus, with no traversing thylakoids present.     

Fascioloides magna (Bassi, 1875) in feral swine from southern Texas.

Between 1971 and 1975, Fascioloides magna was found in 46 of 67 (69%) feral swine (Sus scrofa) in southern Texas. Flukes were recovered from swine in areas where F. magna commonly has been recovered from white-tailed deer and cattle. One to 12 flukes were recovered from each infected animal. Their presence was indicated by black hematin pigment on the liver and various other internal organs. Eggs were not detected in the gallbladder or feces of infected animals although mature flukes and eggs were recovered in the livers suggesting that, like cattle, feral swine can be infected but are aberrant hosts for the parasite and do not disseminate eggs.     

Induction of egg maturation and oviposition in the tick Ornithodoros parkeri (Acari: Argasidae)

Hemocoelic injection and vaginal insertion of selected male reproductive and non-reproductive tissue homogenates into fed-virgin female Ornithodoros parkeri stimulated varying degrees of ovum maturation and/or oviposition during 14 and 30 day observation periods, respectively. Mean times for oviposition and mean numbers of eggs laid per ovipositing female receiving hemocoelic injections of male reproductive tissue homogenates did not differ significantly from fed-mated controls. In addition, hemocoelic injection of male salivary glandular homogenate induced oviposition, yet synganglial homogenate did not. Although vaginal insertion induced both ovum maturation and oviposition, the effect was not as pronounced as when similar doses were administered by hemocoelic injection. These results indicate that a complex interrelated series of precopulatory and copulatory stimuli are necessary for oviposition to occur in fed O. parkeri.