A selective differential medium for the isolation of Listeria monocytogenes

A new medium has been developed for the isolation of Listeria monocytogenes from clinical specimens with a mixed flora. Almost complete inhibition of unwanted organisms was achieved and recognition of colonies of Listeria spp. was usually possible after 24 h using the aesculin-ferric ammonium citrate indicator system. Compared to McBride agar the new medium was more inhibitory to representative contaminating species in pure culture and more successful in isolating small numbers of L. monocytogenes from artificially seeded clinical specimens.     

Potency of microwave irradiation during fixation for electron microscopy

Liver, skeletal muscle, peripheral nerves, pancreas, thyroid and adrenal cortex were prepared for electron microscopy employing microwave energy either during prefixation with glutaraldehyde or instead of prefixation. Microwave irradiation in the presence of glutaraldehyde in Na/K-phosphate or Na-cacodylate containing CaCl2 and MgCl2 led to distinct appearance of membranes, mainly plasma membrane, and membranes of SER, Golgi complex and mitochondria in liver, pancreas and muscle. The area of high quality fixation, however, was limited to the periphery of samples. On the other hand, SER was dilated in cells of the adrenal cortex, and RER markedly vacuolated in thyroid follicular cells. Microwave irradiation in the presence of Na/K-phosphate and subsequent osmication resulted in preservation of the ultrastructure in similar quality as was obtained by osmication without previous immersion in glutaraldehyde. However, the preservation of SER and Golgi complex in liver and pancreas, and of mitochondria in muscle was greatly improved. Small myelin sheaths remained intact whereas large ones showed focal disintegration. We consider that enhancement of fixation by microwave energy may greatly improve preservation of membranes in some tissues. Successful fixation depends on the use of glutaraldehyde during microwave irradiation, the type of buffer, the addition of ions to increase stabilization, the exposure time to heat, and on postosmication.     

Spatial interactions in rapid pattern discrimination

We measured reaction times (RTs) for identification of a target among distracters under stabilized image conditions in which the positions of the target and the distracters were constant within a single experimental session. Under these conditions, the observer need not search for the target because its position is known. We nevertheless found that the presence of even a single distracter could elevate RTs. The magnitude of this effect depended on the distance of the distracter from the target and, for some observers, the distance of the distracter from the fovea. When we added not one but six background elements in a ring around the target, RT increased even more. If, apart from these neighboring distracters, the target was surrounded by more distracters located beyond the nearest neighbors, RT was, in general, not increased further. These findings suggest that adding background elements in a search task can elevate RTs in ways that are not dependent on the positional uncertainty of the target.     

Influence of ethanol on the activities of 3-hydroxy-3-methylglutaryl-coenzyme A-reductase and squalene-hopene-cyclase in Zymomonas mobilis

Summary The influence of different primary aliphatic alcohols on the activities of two key enzymes in hopanoid biosynthesis of Zymomonas mobilis was investigated. By use of ¹⁴C- and ³H-labelled substrates the enzymes 3-hydroxy-3-methylglutaryl-CoA-reductase and squalene-hopenecyclase were detected with activities of 1.6 pmol x (min x mg protein)^-1 and 2.3 pmol x- (min x mg protein)^-1, respectively. Cells grown in the presence of 6% (v/v) ethanol did not show higher activities of these enzymes than cells grown in the presence of 1% (v/v) ethanol. Furthermore, 3-hydroxy-3-methylglutaryl-CoA-reductase was not activated by ethanol. However, ethanol activated the squalene-hopene-cyclase when added to the enzyme test system. Besides ethanol, propanol also had a positive effect on the squalene-hopene-cyclase: the enzyme's activity increased 1.7-fold in the presence of either alcohol at a concentration of 6% (v/v). This corresponded with a similar increase of hopanoid content of whole cells when grown in the presence of 6% (v/v) added ethanol or propanol. These results indicated that the squalene-hopene-cyclase has a regulatory function in the alcohol dependent hopanoid biosynthesis of Z. mobilis.Abbreviation HMG-CoA-reductase 3-hydroxy-3-methylglutaryl-coenzyme A-reductase     

Neural activity pattern is not necessary for the development of adult ultrastructure in katydid (Neoconocephalus robustus) singing muscles

Summary The singing muscles of the katydid Neoconocephalus robustus develop adult ultrastructure late in the last nymphal instar and during the first few days of adult life. The ultrastructural changes during early adulthood were not affected by unilateral axotomy shortly after the adult molt. Both denervated and innervated muscles developed adult proportions of mitochondria, myofibril, and sarcoplasmic reticulum and transverse tubules.     

The electrochemical proton potential generated by the sulphur respiration of Wolinella succinogenes

Wolinella succinogenes grown on formate and elemental sulphur was found to use the polysulphide derivatives 2,2-tetrathiobispropionate (R₂S₄) or pentathionate (S₅O ₆ ⁼ ) as acceptors for formate oxidation. The specific activities of formate oxidation with these acceptors were similar to those with elemental sulphur. The main reaction products of R₂S₄ reduction were 2,2-dithiobispropionate (R₂S₂) and sulphide. Pentathionate was converted to thiosulphate and some elemental sulphur. The electrochemical proton potential across the cytoplasmic membrane of the bacterium was measured in the steady state of electron transport from formate to R₂S₄. The electrical proportion () of the determined through the distribution of labeled tetraphenylphosphonium cation was obtained as 0.17 Volt. The was zero, when a protonophore was present. The pH-difference across the membrane was negligible. Thus the generated by sulphur respiration is close to that measured earlier with fumarate as the terminal acceptor of electron transport.Abbreviations DMO 5,5-dimethyloxazolidine-2,4-dione - R₂S_n (n=2–5) 2,2-polythiobispropionate - TTFB 4,5,6,7-tetrachloro-2-trifluoromethylbenzimidazol - TPP tetraphenylphosphonium cation     

Recovery of rat mast cells after secretion: a morphometric study

Granule reconstitution in rat peritoneal mast cells following massive secretion was studied by morphometric techniques. Immediately following secretion, the earliest identifiable mast cells showed a substantial decrease in cell volume associated with granule loss. Cell volume then increased almost to the original level over a period of a month. The size of the Golgi apparatus increased markedly in the week following secretion and then returned to its original size. The total volume of granules increased slowly after the secretory depletion and by 34 days had not returned to the original value although the number of granules had recovered fully. The reconstitution of mast cells after secretion is a prolonged process with several phases resulting in mast cells of varying appearance and content. This heterogeneity generated by reconstitution post secretion must be considered in studies of populations of mast cells in vivo.     

Non-C-G recognition sequences of DNA cytosine-5-methyltransferase from rat liver

The eukaryotic DNA cytosine-5-methyltransferase (E.C.2.1.1.37) is known to methylate cytosine in DNA mainly, but not exclusively in C-G. In the present study the minor, non-C-G recognition sequences of a rat DNA methyltransferase were analyzed by Maxam-Gilbert sequencing of in vitro methylated SV40 DNA. The enzyme methylates C-A and C-T at a 50-fold lower initial rate than C-G. Methylation of C-C at the 5'C was not observed in the piece of DNA sequenced. The methylation of C-A is very low in the trinucleotides ACA and CAC, the other C-A containing trinucleotides in DNA are much better methylacceptors. C-T was found methylated predominantly in the sequences CCTAA, ACTAA, and ACTGT. A comparison of the activity with different substrates is in favour of the enzyme making its recognition in the major groove of the DNA.     

Protein kinase C inhibition by calmodulin and its fragments

Inhibition of protein kinase C (PKC) by calmodulin is investigated and we describe the localization of inhibitory sequences within the calmodulin molecule. We present evidence that calmodulin inhibits PKC through an inhibition of the activation of PKC associated with lipid membranes: Binding of PKC to lipid vesicles is not affected, but activation is abolished. The potent calmodulin antagonist R24571 (calmidazol) did not affect the inhibition of PKC by calmodulin at concentrations up to 10^–5 M. Two tryptic fragments of calmodulin were isolated which inhibited PKC. They were only slightly less potent than intact calmodulin with an IC₅₀ of 6 µ M compared to 1 µ M of intact calmodulin. They were identified as Ser³⁸-Arg⁷⁴ and His¹⁰⁷-Lys¹⁴⁸. Each of the inhibiting fragments contains an intact Ca²⁺-binding domain with complete helix-loop-helix structure (EF hand). Other calmodulin peptides showed only weak inhibitory activity. Both fragments did not stimulate cAMP phosphodiesterase even at concentrations 100-fold higher than the calmodulin concentration needed for maximal stimulation. None of the fragments acted as a calmodulin antagonist.