Modified Littman Oxgall Agar to Isolate Cryptococcus neoformans

Littman Oxgall Agar was modified by adding an extract of Guizotia abyssinica seeds with a water diluent for rehydration. In this medium, colonies of Cryptococcus neoformans became brown, but the color failed to develop in eight other yeasts and yeast phases of diphasic organisms. The depression of saprophytic fungi noted on Littman Oxgall Agar was not lost in the modification.     

Stability of Suspensions of Influenza Virus Dried to Different Contents of Residual Moisture by Sublimation In Vacuo

After freezing, suspensions of influenza virus were dried by sublimation of water in vacuo to contents of residual moisture of 3.2, 2.1, 1.7, 1, or 0.4%. The stability of the several suspensions was determined by an accelerated storage test. Based on the times predicted for the dried preparations stored at different temperatures to lose 1 log of infectivity titer, the order of stability in relation to residual moistures was as follows: 1.7% > 2.1% > 1% > 3.2% > 0.4%.     

Calculation of melting curves for DNA

A method is reported for calculating the melting curve of a DNA molecule of random base sequence, including in the formalism the dependence of the free energy of base pair formation on the size of a denatured section. Some explicit results are shown for a “typical” base sequence, in particular the probability of helix formation at individual base pairs in several different regions of the molecule and the amount of melting from the end of the chain. Particular attention is drawn to the variation of local melting behavior from one region of the molecule to another. It is found that sections rich in AT melt at relatively low temperatures with a fairly broad transition curve, whereas regions rich in GC pairs melt at higher temperatures (as expected) with a very abrupt, local transition curve. To account qualitatively for the results one may divide melting into two kinds of processes: (a) the nucleation and growth of denatured regions, and (b) the merging together of two denatured sections at the expense of the intervening helix. The first of these processes dominates in the first stages of melting, and leads to rather broad local melting curves, whereas the second process predominates in the later stages, and occurs, in a particular part of the molecule, over a very narrow temperature range. It is estimated that the average length of a helix plus adjacent coil section at the midpoint of the transition is approximately 600 base pairs. Since transition curves which measure the local melting behavior reflect local compositions fluctuations, these curves contain information about the broad outlines of base sequence in the molecule. Some suggestions are made concerning experiments by which this potential information source could be exploited. In particular, it is pointed out that one might hope to map AT or GC rich regions at particular genetic loci in a biologically active DNA molecule. Values of the relevant parameters found earlier for the transition of homopolymers produce melting curves for a DNA of random base sequence which are in good agreement with the experimental transition curve for T2 phage DNA. Hence the present theoretical picture of the melting of polynucleotides is at least internally self-consistent.     

Murine Toxicity of Agrobacterium tumefaciens

Eleven strains of the crown gall organism, Agrobacterium tumefaciens, tested by intraperitoneal injection into mice, were lethal within 48 hr. Five other species had some lethal strains. The lethal effect of A. tumefaciens appeared to be the result of a toxic rather than an infectious process, since histopathological anomalies were not found in mice injected with live cultures and since heat-killed cultures were lethal. The murine toxin disappeared when A. tumefaciens was grown at 36 C and reappeared when the organism was subsequently incubated below 30 C. The murine toxin itself was not inactivated by exposure to 100 C for 30 min. The toxin was associated with the cells and was not excreted into the medium. Centrifugal fractionation revealed that the toxin was associated with the smaller cells in 3-day stationary-phase cultures. These data suggested a possible relationship between toxin production and the production of the agents responsible for the initiation of plant tumors.     

Application of a Theory for Circumnutations to Geotropic Movements

From a previously published theory (Israelsson and Johnsson 1967) for circumnutations in Helianthus annuus it is possible to predict the geotropical curvatures of the hypocotyls. This extension of the theory is given in the present paper and some geotropical experiments are performed and discussed. The agreement between the theory and the experiments has been verified in the case of gravitational stimulation during relatively short stimulation periods, in the case of continuous gravitational stimulation, etc. Restrictions in the proposed model are discussed.     

Toxicity of some goldenrods

This study was performed to determine the biological activity in mice of eight species of Solidago (goldenrod) and to determine some of the chemical groups present in these species. Biologically active substances were present in all of the species tested. Tests of six species were positive for alkaloids. All but one of the species contained demonstrable saponins. All of the species contained tannins, whereas six or seven species were positive for flavonoids. Quaternary bases were not found in any of the species tested. A comparison of the biological activity in mice of these species of Solidago, extracts of which were injected intraperitoneally, showed their descending order of activity to be: (1)S. flexicaulis L., (2)S. hispida Muhl., (3)S. juncea Ait., (4)S. serotina Ait., (5)S. canadensis L., (6)S. rugosa Ait., (7)S. uliginosa Nutt., and (8)S. squarrosa Muhl.     

AN ELECTRON MICROSCOPE STUDY OF MYOFIBRIL FORMATION IN EMBRYONIC CHICK SKELETAL MUSCLE

The formation of myofibrils in the developing leg muscle of the 12-day chick embryo was studied by electron microscopy. Myofilaments of two varieties, thick (160–170 A in diameter) and thin (60–70 A in diameter), which have been designated myosin and actin filaments, respectively, on the basis of their similarity to natural and synthetic myosin and actin filaments, appear in the cytoplasm of developing muscle cells. There is a greater than 7:1 ratio of thin to thick filaments in these young myofibers. The free myofilaments become aligned in the long axis of the cells, predominantly in subsarcolemmal locations, and aggregate into hexagonally packed arrays of filaments. The presence of Z band material or M band cross-bridges do not appear to be essential for the formation or spacing of these aggregates of filaments. Formation of the Z band lattices occurs coincidentally with the back-to-back apposition of thin filaments. An hypothesis concerning myofibril growth, based on the self-assembly characteristics of the filaments, is presented.     

Nickel Substitution for Calcium in Excitation-Contraction Coupling of Skeletal Muscle

In 1962 Frank (22) reported that the addition of any one of a number of divalent cations, including Ni, to a Ca-free Ringer solution prevented the rapid loss of contractility seen in the absence of external Ca. To investigate further the Ni-Ca substitution, studies were made of ⁴⁵Ca and ⁶³Ni exchange during contraction and at rest using frog striated muscle. In contrast to ⁴⁵Ca, it was found that there is no increase of ⁶³Ni uptake associated with a K contracture of the sartorius muscle. The rates of loss of ⁶³Ni and ⁴⁵Ca from resting toe muscles previously bathed in the respective radioisotopes are not significantly different. Resting and action potentials, after 1 hr in a Ringer solution with Ni replacing Ca, closely resemble these potentials in normal Ca-Ringer's solution. Studies on the syneresis of isolated myofibrils indicate that Ni cannot replace Ca in activating this reaction. It is suggested that Ca is required for at least two steps in E-C coupling: one is the spread of excitation at the sarcolemma and transverse tubular system; the second is the activation of actomyosin ATPase. Conceivably Ni can substitute for Ca in the former but not in the latter.     

Physicochemical and Biological Properties of Sonically Treated Vi Antigen

Electrophoretically purified Vi antigen from Citrobacter freundii 5396/38 was depolymerized by sonic treatment. The treatment caused an 80% reduction in specific viscosity and a reduction in molecular weight from 1.6 x 10(6) to 3.9 x 10(4). The O-acetyl and N-acetyl contents of the antigen and its infrared spectrum remained unchanged. The sonically treated antigen was only 1% as effective as the original antigen in eliciting protection in mice against challenge with Salmonella typhi. Sonically treated antigen also elicited lower antibody titers after single injections in mice and rabbits. No loss in ability to precipitate antibody or to sensitize red blood cells for hemagglutination was observed.