Resistance to Osborne's Cyst Nematode in Selected Nicotiana Species

Resistance to an undescribed species of Heterodera, Osborne''s cyst nematode, was compared in Nicotiana glutinosa, N. paniculata, N. plumbaginifolia and N. Iongiflora. These species were differentially resistant in greenhouse tests as shown by nematode development, the reaction of the invaded roots, and the expression of resistance in interspecific hybrids.     

Attractant-Directed Motility in Escherichia coli: Requirement for a Fluid Lipid Phase

Attractant-directed motility (chemotaxis) in Escherichia coli has an absolute requirement for a fluid membrane. No such requirement was detected for motility per se.     

DNA values in somatic tissues of Dermestes (Dermestidae: Coleoptera)

The distribution of DNA values in some somatic tissues of seven Dermestes species has been investigated. In all cases the DNA values are distributed as members of a doubling series. Distributions are found to be similar between species and sexes for the same tissue but different between tissues in the same species. Species DNA values derived from somatic tissues agree with DNA values previously determined for spermatids. These data are discussed in relation to the range of species DNA values (2.7 x) and the process of differentiation.     

Procedure for Evaluating the Effects of 2,450- Megahertz Microwaves upon Streptococcus faecalis and Saccharomyces cerevisiae

Modifications of a commercial 2,450-megahertz microwave oven were made so that 6 ml of microbial suspension could be exposed to the microwave field for various periods of time. The microorganisms were contained in the central tube of a modified Liebig condenser positioned in the approximate geometric center of the oven cavity. Kerosene at -25 C was circulated through the jacket of the condenser during microwave exposure permitting microwaves to reach the microbial suspension. Flow rates of the kerosene were varied to permit the temperature of the suspension to range from 25 to 55 C during microwave exposure. Conductive heating experiments using similar temperatures were also conducted. A thermocouple-relay system was employed to measure the suspension temperature immediately after the magnetron shutoff. Continuous application of microwaves to suspensions of 10(8) to 10(9)Streptococcus faecalis or Saccharomyces cerevisiae per ml appeared to produce no lethal effects other than those produced by heat. Respiration rates of microwave-exposed Scerevisiae were directly related to decreases in viable count produced by increased microwave exposure times.     

Copper sulfide precipitation by yeasts from Acid mine-waters

Two strains of Rhodotorula and one of Trichosporon precipitated dissolved copper with H₂S formed by reducing elemental sulfur with glucose. Iron stimulated this activity under certain conditions. In the case of Rhodotorula strain L, iron stimulated copper precipitation aerobically at a copper concentration of 18 but not 180 μg/ml. Anaerobically, the L strain required iron for precipitation of copper from a medium with 180 μg of copper per ml. Rhodotorula strain L was able to precipitate about five times as much copper anaerobically as aerobically. The precipitated copper was identified as copper sulfide, but its exact composition could not be ascertained. Iron was not precipitated by the H₂S formed by any of the yeasts. Added as ferric iron, it was able to redissolve copper sulfide formed aerobically by Rhodotorula strain L from 18 but not 180 μg of copper per ml of medium. Since the yeasts were derived from acid mine-waters, their ability to precipitate copper may be of geomicrobial importance.     

The effects of X-rays on the chromosomes of locust embryos

Irradiation of Schistocerca gregaria embryo cells during the S and G₂ stages of interphase produces the same general classes of chromatid aberration as have been seen in organisms, such as Vicia faba, which have been used widely in radiocytological work. In addition, however, a series of intrachange aberrations has been found which is novel. In order to account for these Revell's exchange hypothesis has been extended to include the involvement of isolocus primary lesions. The exchange-type hypothesis is preferred because it can more readily accomodate the whole spectrum of aberrations found.     

Environmental effects on bacterial copper extraction from low-grade copper sulfide ores

In bacterial extraction of copper from low-grade copper sulfide ores, at least three contributions are made by Thiobacillus ferrooxidans. They are: (1) enzymatic oxidation and consequent solubilization of insoluble sulfides; (2) regeneration of ferric lixiviant for chemical oxidation and solubilization of insoluble sulfides; and (3) partial fixation of externally introduced iron in the ore. Although it is not possible at the present time to measure each of these contributions separately, it is possible to measure the combined contributions. Such measurements reveal a strong dependence of extraction efficiency on various physical, chemical, and biological factors. The following physical factors may affect the rate of bacterial copper extraction: particle-size of ore, oxygen and carbondioxide supply, oxidation-reduction potential, pH, temperature, adsorption and ion exchange capacity of ore, and surface tension effects. The following chemical factors may influence the rate of copper extraction: the mineralogy of the ore, the nature of the gangue, the distribution of the sulfide minerals in the host rock, the external supply of ferrous or ferric iron, and the availability of inorganic and organic nutrients. Finally, the following biological agents in addition to T. ferrooxidans may influence the rate of copper extraction: fungi, protozoa, Thiobacillus thiooxidans, and heterotrophic bacteria. Proper control of these various factors is essential for efficient bacterial extraction of copper from low-grade ore. It is recognized that the foregoing environmental factors also influence chemical copper extraction.     

The synthesis of polydeoxyribonucleotide by cell-free extracts of embryonic mouse tissue

The conditions under which soluble extracts prepared from mouse embryos incorporate [(3)H]thymidine 5'-triphosphate into polydeoxyribonucleotide have been studied. In common with similar preparations from other mammalian tissues, mouse-embryo DNA nucleotidyltransferase requires the four complementary deoxyribonucleoside 5'-triphosphates, primer DNA and a bivalent cation for activity. Unlike other mammalian DNA nucleotidyltransferases, the rate and extent of the incorporation of [(3)H]thymidine 5'-triphosphate is much greater with Mn(2+) than with Mg(2+) and, with either Mg(2+) or Mn(2+), maximum activity occurs at pH6.4. The difference between Mg(2+) and Mn(2+) varies markedly with pH, reaching a maximum of six- to eight-fold at pH6.4.