Activity of a “thermostable exotoxin” of Bacillus thuringiensis subsp. morrisoni in the Salmonella/microsomal assay for bacterial mutagenicity

The purpose of this study was to employ the Salmonella/microsomal assay (Ames test) to investigate the mutagenic potential of a thermostable exotoxin of Bacillus thuringiensis subsp. morrisoni. Bacteria are ideal for the detection of infrequently occurring point mutations because the large number of organisms (200 to 400 million bacteria per plate) exposed to the mutagen at any one time increases the possibility of observing a random mutational event. The exotoxin used in this study was produced using the shaker flask fermentation procedure with mineral casein broth. A Petri dish method of bioassay using fresh bovine feces was used to determine the efficacy of the exotoxin against horn flies. The LD₅₀ was found to be 5.35 μl/g of feces. Five bacterial tester strains were identified and characterized for the genetic markers described by Ames et al. (B. N. Ames et al., 1975, Mutat. Res., 31, 347–364). Appropriate doses of the B. thuringiensis supernatant, solvent or positive control were added to agar plates. The supernatant was tested at five dose levels against all five strains of bacteria. Controls of bacteria only were included for spontaneous reversions. All treatments were performed in triplicate. The numbers of revertant colonies from each set of triplicate plates were averaged and the standard deviation calculated and compared to that found with the solvent control. The negative controls, positive controls, and sterility controls all fulfilled requirements for determination of a valid test. No detectable mutagenic activity was found for the thermostable exotoxin of B. thuringiensis morrisoni.     

Revision of SAT chromosome number in Triticum monococcum with respect to nucleolar organizers activity

Summary Six varieties of Triticum monococcum were analysed by means of the nucleolar test; i.e., estimation of the maximum number of primary nucleoli per nucleus. All of the varieties exhibited 4 primary nucleoli in telophase and early interphase. Following detailed karyological analysis four SAT chromosomes in all six karyotypes were found in accordance with the maximum nucleolar number. Secondary constrictions and microsatellites were localised on the short arms of chromosome pairs 3 and 5. A new order of the chromosomes in the idiogram of Tr. monococcum is proposed.     

Effect of pH,mono- and divalent cations on the mixing of phosphatidylglycerol with phosphatidylcholine. A monolayer (π, ΔV) and fluorescence study

The mixing of various molecular species of phosphatidylglycerol and phosphatidylcholine differing in their acyl chain lengths has been studied both in monolayers (π, Δ$\text{V}$), and in water dispersions (fluorescence polarization) with varying pH and ionic strength of the aqueous phase and in the presence of the divalent cations Mg²⁺ and Ca²⁺. In dilauroylphosphatidylglycerol/dipalmitoylphosphatidylcholine mixtures, both in monolayers and in water dispersions, no phase separation was detected at pH 2.9 where phosphatidylglycerol was protonated. With dipalmitoylphosphatidylglycerol/dipalmitoylphosphatidylcholine mixtures, in monolayers and at the same pH, no phase separation was detected for surface pressures below $\text{π = 40}\text{mN}\text{·}\text{m}{}^{\mathrm{?1}}$. In monolayers, and under ionic conditions such that phosphatidylglycerol was ionized (pH 5.6, 10 mM NaCl) miscibility was observed with dilauroylphosphatidylglycerol and dipalmitoylphosphatidylcholine and also with dipalmitoylphosphatidylglycerol and dilauroylphosphatidylcholine. Varying the ionic strength did not alter the miscibility of these lipids. The divalent cations Mg²⁺ and Ca²⁺ did not modify that of dilauroylphosphatidylglycerol with dilauroylphosphatidylcholine or with dipalmitoylphosphatidylcholine. Both in monolayers and in water dispersions, dipalmitoylphosphatidylglycerol and dilauroylphosphatidylcholine appeared to be at least partly miscible, in the presence of magnesium. Only in the presence of calcium and at high surface pressure might the monolayer data account for phase separation between these two lipids. The data presented demonstrate the existence of strong cohesive forces between phosphatidylcholine and phosphatidylglycerol with a marked influence of the former on the physical state of the latter. From an analysis of the Δ$\text{V}$ data, it is suggested that intrafacial hydrogen bonds may play a significant role in stabilizing phosphatidylcholine/phosphatidylglycerol mixtures.     

A micromethod for the quantitative determination of the viability of Candida albicans hyphae

A micromethod for the quantitative determination of the viability of Candida albicans hypae was devised which takes advantage of the dimorphic nature of C. albicans which grows exclusively in the yeast form when incubated aerobically on Sabouraud dextrose agar at 30°C. When tested by thisd method, all viable, C. albicans hyphae were recognized as microcolonies consisting of one hypha surrounded by several yeast form progeny. In contrast to this, no yeast form progeny emerged from nonviable hypae. By counting appropriate total numbers (200–400) of microcolony-forming hypae and infertile hyphae, it was possible to determine the ratio of viable to nonviable cells in a given hyphal suspension. This micromethod may be used for quantitative assessment of the candidacidal effects of various antimycotic agents or phagocytes C. albicans hyphae whose viability could not have been determined by the conventional plating technique because of the species' high propensity to clump.     

Characterization of a pilot plant airlift tower loop bioreactor: II. Evaluation of global mixing properties of the gas phase during yeast cultivation

Saccharomyces cerevisiae was cultivated in a 4-m(3) pilot plant airlift tower loop reactor with a draft tube in batch and continuous operations and for comparison in a laboratory airlift tower loop reactor of 0.08 m(3) volume. The reactors were characterized during and after the cultivation by measuring the distributions of the residence times of the gas phase with pseudostochastic tracer signals and mass spectrometer and by evaluating the mixing in the liquid phase with a pulse-shaped volatile tracer signal and mass spectrometer as a detector. The mean residence times and the intensities of the axial mixing in the riser and downcomer, the circulation times of the gas phase, and the fraction of the recirculated gas phase were evaluated and compared.