Rhodosporidium Banno: dose-effect relations, mutagenic efficiency, and spectrum of mutants in the induction of auxotrophic mutants by ultraviolet light and N-methyl-N'-nitro-N-nitrosoguanidine

The kinetics, efficiency, and specificity of induction of forward mutations to auxotrophy by ultraviolet light (UV) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was examined in stationary phase cells of Rhodosporidium (Rhodotorula) wild strain Rg1. In comparison to the spontaneous level the frequency of auxotrophic mutants was increased more than 1000 times by both mutagens, however, the mutagenic efficiency of MNNG was higher than that of UV. We found that the forward mutation rate is a linear function of the applicated UV and MNNG doses in the range to 600 J m-2 or 25 mM X min, respectively. The 35 studied biosynthetic pathways to amino acids, purines, pyrimidines, and vitamins are genetically blocked at different frequencies, but there is not any significant difference between UV and MNNG induced frequencies of mutants with a specific requirement. However, in difference to the approximately equal distribution of the MNNG-induced nic mutants among the genetic blocks of the tryptophan-nicotinamide pathway, UV-induced nic mutants occurred with a higher frequency in the genes of the tryptophan pyrrolase and the 3-hydroxykynureninase than in the genes of the other enzymes of the pathway.     

Immunochemical study of the antigenic structure of bacteria of genus Bordetella. IV. Fractionation of B. pertussis extracts and study of the immunochemical and biological properties of the isolated fractions]

Fractionation of an extract of pertussis microbes was carried out with the aid of gel-filtration on Sephadex G-100, ion-exchange chromatography on DEAE-cellulose, and preparative electrophoresis. Fractions differing in serological, immunogenic activity and the content of antigenic components were isolated. In using the method of gel-filtration of sefadex G-100 the greatest serological, immunogenic and histamine-sensitizing activity was possessed by the high-molecular fraction containing 8 of 11 antigenic components detected in the initial extract. The antigenic components were distributed into 5 fractions by the ion exchange chromatography on DEAE-cellulose. The greatest serological activity was possessed by fractions exiting from the column at the 0.01--0.04M interval of the phosphate buffer concentration. A method of preparative electrophoresis from the pertussis microbes extract was applied and two fractions were isolated from the anode and the cathode zones, each containing 4 antigenic components only, but possessing serological and immunogenic activity and having no histamine-sensitizing properties.     

Use of germ-free mice in experimental transplantation

A comparative study of skin allografts was performed in germ-free A/Ola mice kept in boxes and in A/Ola and BALB mice raised in ordinary conditions. Skin graft (of C57B1/6 mice) in A/Ola and BALB mice raised in ordinary conditions was shown to reject 16-21 and 12-18 days after the transplantation, respectively without cyclophosphamide (CP) use. CP application in BALB mice, grown in ordinary conditions, prolonged the lifespan of grafts to 12-29 days. The use of CP in germ-free A/Ola mice prolonged the lifespan of grafts to 19-39 days. In germ-free mice kept in boxes the use of an immunodepressant was not accompanied by infectious complications, while the animals kept in the vivarium often died of infectious diseases.     

Enzyme-Linked Immunosorbent Assay of Ampicillin in Milk

An indirect immunoassay for quantitative determination of ampicillin (range, 10–1000 ng/ml) in buffer or milk has been developed. Polyclonal antibodies were obtained against ampicillin conjugated with bovine serum albumin; the conjugate was synthesized by direct condensation using carbodiimide. The antibodies were specific for ampicillin and exhibited low cross-reactivity to other penicillins (azlocillin, 17%; penicillin G, 10%; piperacillin, 5%; and carbenicillin, 4%). Matrix effects were minimized by combining the use of a casein-supplemented buffer (content of casein, 1%) with sample dilution. Limit of detection for ampicillin in milk (diluted tenfold) was equal to 5.0 ng/ml (which corresponded to 50 ng/ml of the original sample).     

Resistance to antibiotics and heavy metal salts of coagulase-positive staphylococci belonging to different biological types (ecovars)

A total of 189 strains of S. aureus isolated from cows, sheep, swines, poultry, monkeys, rabbits, foxes, and humans and 23 strains of S. intermedius isolated from minks and sables were studied. The staphylococci belonged to different biological types (according to the Hajek-Marsalek's scheme) and ecovars (according to the Meyer-Witte's scheme). The strains were studied with respect to their resistance to 10 antibiotics (benzylpenicillin, streptomycin, tetracycline, levomycetin, erythromycin, oleandomycin, neomycin, kanamycin, monomycin, and novobiocin), mercuric chloride and cadmium sulfate. As a whole the frequency of resistance to the above preparations among the staphylococci of the animal origin was not high. Differences in the frequency and range of the resistance between strains belonging to different biological types (ecovars) were shown. The highest number of the resistant cultures was detected among the strains of the biological type E (ecovar canis) and atypical strains of S. intermedius isolated from the minks. The least number of the resistant cultures was detected among the strains of the biological type C1 (ecovar bovis) isolated from the cows. It was found that almost all strains of S. intermedius were resistant to cadmium sulfate. This may be used as an additional characteristic of the species.     

Determination of ivermectin in bovine liver by optical immunobiosensor

A rapid and sensitive biosensor immunoassay was developed for residues of the antiparasitic agent ivermectin in bovine liver. A detection limit of 19.1 ng g(-1) was achieved. The sensor employed was a Biacore optical instrument based on surface plasmon resonance. 5-O-succinoylivermectin-apo-transferrin conjugate was used to produce monoclonal antibody while a second derivative, ivermectin-oxime, was immobilised onto the surface of a sensor chip. A range of assay parameters (flow rate, injection time, temperature) and extraction techniques were investigated. In the final assay procedure, ivermectin was extracted with acetonitrile followed by C(8) SPE clean-up. Matrix effect was minimised by increasing the flow rate to 25 microl min(-1) and reducing the sample injection time to 2 min. The average value for liver samples spiked at 100 ng g(-1) (the MRL for the drug) and 50 ng g(-1) concentrations were 93.7 and 43.2 ng g(-1), respectively.     

Differences in functional organization of the visual center in frogs and cats

Functional characteristics of responses of tectal neurons in the frog and the primary visual cortex of the cat obtained under indentical experimental conditions during changes in the brightness and duration of flashes within the range of 6 log units were compared. In frogs most units have short summation times and relatively lower thresholds; the response latency is 5–7 times longer than in cats. The overwhelming majority of tectal units can respond only to a narrow range of photic energy that differs for different cells. Most cells in cats respond to changes in brightness of between 4 and 5 log units; they have long summation times, short latent periods, and relatively higher thresholds. The differences found on comparison of the various functional characteristics of the cells in the visual center show that frogs have fixed mechanisms of temporal and spatial interaction responsibile for detection of stimulus brightness. In cats this interaction between individual cell populations and this mutual inhibition between adjacent cells are not prominent. The increased complexity and overlapping of interneuronal connections leads to convergence of day and twilight vision stimuli on the same neuron and to the ability of single units to respond to the whole "working" range of light brightness for the cat visual system.     

A new method for finding long consensus patterns in nucleic acid sequences

We describe a fast computer algorithm for identifying consensuspatterns in DNA sequences. The method requires no prior assumptionsabout the consensus pattern other than its length. In particularno previous knowledge of the frequency or spacing of consensuspatterns is required. However, a priori information about theshape of the consensus pattern, or invariability of individualpositions, or the overall conservation level, can be utilizedto enhance the selectivity and sensitivity of search. As thenumber of all possible consensus words increases very rapidlywith length, comprehensive searches have usually been restrictedto a maximum of 10–12 nucleotides, even when large mainframesare used. Our algorithm enables searching for consensus patternsof this order on current mid-range and powerful microcomputers.Searches may be conducted on single, long sequences or a setof possibly aligned shorter sequences. We give examples of identifiedconsensus patterns in both prokaryotic and eukaryotic DNA sequences,along with some typical program timings. Received on January 14, 1991; accepted on March 5, 1991