Markovian neural networks

The neural network that efficiently and nearly optimally solves difficult optimization problems is defined. The convergence proof for the Markovian neural network that asynchronously updates its neurons' states is also presented. The comparison of the performance of the Markovian neural network with various combinatorial optimization methods in two domains is described. The Markovian neural network is shown to be an efficient tool for solving optimization problems.     

Streptomycin and N-Methyl-N’-nitro-N-nitroso-guanidine inhibit incorporation of14C-precursors of macromolecule synthesis inEuglena gracillis

Streptomycin and N-methyl-N’-nitro-N-nitrosoguanidine (MNNG) cause a 100% hereditary bleaching ofEuglena gracilis. In spite of the outcomes being the same, the corresponding mechanisms differ. By investigating the incorporation of the¹⁴C-labelled precursors of macromolecule synthesis we showed streptomycin to inhibit the synthesis of nucleic acids and proteins to the same extent (56%), whereas in the case of MNNG a 66% inhibition of nucleic acid synthesis and a 24% one of protein synthesis were observed.     

Mycobacteria in the light of modern genetics development

It is generally assumed that genetic research of mycobacteria is delayed as compared with other, more commonly used, bacterial models, particularly in the field of genetic transfers. In the field of mutagenesis the problems have been studied to such an extent that replication maps of the chromosome of M. phlei and M. tuberculosis H37 Rv have already been constructed and a new model of the cell cycle of bacteria exhibiting a slow growth rate has been worked out. When the problems of mycobacterial genetics are looked upon in the light of gene manipulations it may be concluded that mycobacteria belong to a few models whose genes are used for cloning and that problems of practical significance will be studied by means of the most modern approaches.     

Effect of detergents on aspartate ammonia-lyase activity inEscherichia alcalescens

The effect of twelve detergents on aspartate ammonia-lyase activity of Escherichia alcalescens used for the production of L-aspartic acid was tested. Best permeabilization was found with Triton X-100, Slovafol 910 and Corona, a mixed commercial preparation. In contrast to Triton X-100 and Slovafol 910, a much narrower range of suitable concentrations was observed with Corona.     

Pigmentation changes in Brevibecteria induced by mutagenic treatment

Inducible pigmentation changes were observed in pigmented strains of Brevibacterium sp. M27 and B. flavum treated with N-methyl-N'-nitro-N-nitrosoguanidine. The highest frequency of induction was reached already at a survival of 30-40% with the maximal yield of 6-10%. As compared with the initial yellow colour, three new pigmentation types, viz. white, pink and orange, were observed. The yellow pigmented parent strains are most resistant to the lethal effects of UV radiation. By selecting pigmented mutants of all types on media containing antibiotics it was possible to obtain strains that were resistant either to tetracycline or to streptomycin. Auxotrophic pigmented mutants were also isolated. In multiple mutant strains of Brevibacterium sp. M27 a number of strainsexhibited a changed L-lysine production. In some strains the production was variable, whereasother strains did not produce L-lysine at all and stains with a limited production of other amino acids were also detected.     

Sterol composition of a δ5,7-sterol-rich strain ofSaccharomyces cerevisiae during batch growth

Sterol composition was examined during batch growth on complex media containing ethanol, molasses or glucose as the carbon source. The molasses-grown cells exhibited a balanced sterol composition throughout growth, maintaining the proportion of ergosterol to 24:28-dehydroergosterol equal to 1.4. The negative effect of glucose on sterol synthesis manifested itself by decreasing the accumulation of 24:28-dehydroergosterol and total sterols but not of ergosterol. Using ethanol as the sole carbon source, a large amount of 24:28-dehydroergosterol accumulated, partly at the expense of other sterols. The gradual addition of nitrogen source during growth significantly decreased the accumulation of ergosterol, 24:28-dehydroergosterol and of total sterols. A general scheme of regulation of sterol synthesis in baker's yeast is presented.     

Effect of cyclophosphamide on the candidacidal activity of rabbit peritoneal macrophages

Single and repeated intravenous administration of cyclophosphamide significantly decreased the candidacidal activity of rabbit peritoneal macrophages. Using higher doses of the drug, a more pronounced decrease, persisting up to 10 d, was observed. The phagocytic index has not changed significantly 10 d after cyclophosphamide injection as compared with controls. No changes in the phagocytic activity were recorded. The decreased candidacidal activity may be one of the causes of serious microbial infections in cyclophosphamide-treated patients.     

Characteristics of the saprophytic reference strain FA ofClaviceps paspali

Growth properties and morphological features of the saprophytic collection cultureClaviceps paspali strain FA were investigated. The strain was characterized by a range of utilization of 13 carbon sources in a basic synthetic and a peptone medium. A temperature of 23 °C was more favourable for growth than 28 °C. Stages of changes of the culture cultivated for a long time on Sabouraud’s medium were detected by electron microscopy. The white culture was characterized by true septated mycelium with different types of terminal parts of hyphae. Arthrospores occurred after a 14-d cultivation, small spherical conidia released individually from hyphae were quite rare. As compared with other strains of the same species, strain FA did not form spherical clusters of conidia. On the other hand, a spontaneous rupture of the surface cell wall in different parts of hyphae and release of the cytoplasm were observed. In corn-steep containing media the formation of individual, pair and chain-like forms of arthritic conidia was stimulated. Destructive autolytic changes of hyphae were detected in the medium with potato extract.     

Saprophytic production of Clavine alkaloids and activity of Hydroxymethylglutaryl-CoA reductase

In submerged Claviceps cultures the activity of hydroxymethylglutaryl-CoA reductase preceded the increase of alkaloid production and of sterol content. During the first alkaloid phase, cell mevalonate was involved in the biosynthesis of both alkaloids and steroids. In the second production phase, it was predominantly used for alkaloid synthesis. Hydroxymethylglutaryl-CoA reductase appears to be a suitable target for physiological manipulation to increase clavine alkaloid yields.