abetd-Xylose metabolism in Aureobasidium pullulans: effects of aeration and vitamins

Summary The yeast-like organism Aureobasidium pullulans efficiently converted abetd-xylose to cell mass (Y _X/S=0.45 g·g^–1) with negligible production of polyols (Y _P/S=0.003 g·g^–1) under aerobic conditions. A. pullulans grown semiaerobically exhibited different fermentation capacities in seven basal (vitaminless) medium and medium containing a mixture of seven vitamins. It was found that under semiaerobic conditions a mixture of vitamins significantly enhanced production of ethanol from abetd-xylose, resulting in a 15-fold higher yield coefficient of ethanol (Y _E/S=0.22 g·g^–1) as compared to that achieved in vitaminless medium. This increase in ethanol production was accomplished at the expense of cell mass. A. pullulans produced extremely low amounts of polyols throughout all aerobic and semiaerobic experiments. A. pullulans displayed strictly NADPH-linked xylose reductase and NAD⁺-linked xylitol dehydrogenase activities.     

Transformation of a new Gram-positive methylotroph,Brevibacterium methylicum,by plasmid DNA

Summary Brevibacterium methylicum is a newly isolated Gram-positive facultatively methylotrophic bacterium that uses the NAD⁺-dependent methanol dehydrogenase for methanol oxidation and assimilates its carbon via the ribulose monophosphate cycle. Protoplasts prepared by lysozyme treatment of B. methylicum cells grown in the presence of glycine were transformed by plasmid shuttle vectors pCEM500 (16.5 kb; Sm^r/Sp^r, Km^r/Gm^r) and pEC71 (7.1 kb; Km^r/Nm^r) constructed on the basis of B. lactofermentum plasmid pAM330 and replicating in Escherichia coli and in amino-acid-producing coryneform bacteria. The resistance markers were found to be expressed in B. methylicum and autonomous plasmid DNAs of various size were isolated from the transformants. The presence of the pAM330 replicon in these plasmids was demonstrated by DNA-DNA hybridization experiments. Offprint requests to: J. Nevera     

Cultural characteristics and zearalenone production by strains of<Emphasis Type="Underline">Fusarium</Emphasis> from wheat

Conidia of the speciesFusarium culmorum /W.G.Sm./ Sacc. andFusarium graminearum Schwabe are characterized by variability in zearalenone production and dimensions depending on the substrate. The sporulation of isolates from some wheat eultivars have been deprived in vivo and in vitro in the first passage, but not their pathogenicity and toxic metabolites production. Nonsporulating strains produced lower quantités of zearalenone than sporulating ones. Liquid filtrates of such nonsporulating strains had a high phytotoxic effect on wheat caryopses. The crystalline toxin DAS /0,25 ug/ml/ had low phytotoxic effect on wheat caryopses.     

Assessment of membrane potential changes using the carbocyanine dye,diS-C3-(5): synchronous excitation spectroscopy studies

The fluorescence of the voltage sensitive dye, diS-C₃-(5), has been analyzed by means of synchronous excitation spectroscopy. Using this rather rare fluorescence technique we have been able to distinguish between the slightly shifted spectra of diS-C₃-(5) fluorescence from cells and from the supernatant. It has been found that diS-C₃-(5) fluorescence in the supernatant can be selectively monitored at _exc = 630 nm and _em= 650 nm, while the cell associated fluorescence can be observed at _exc= 690 nm and _em = 710 nm. A modified theory for the diSC₃-(5) fluorescence response to the membrane potential is presented, according to which a linear relationship exists between the logarithmic increment of the dye fluorescence intensity in the supernatant, In I/I°, and the underlying change in the plasma membrane potential, _p=_p-°_p. The theory has been tested on human myeloid leukemia cells (line ML-1) in which membrane potential changes were induced by valinomycin clamping in various K⁺ gradients. It has been demonstrated that the membrane potential change, _p,can be measured on an absolute scale. Offprint requests to: J. Plasek     

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.     

Microflora participating in the decomposition of carboxymethyl cellulose continuously added to the soil

The microbial community in the soil was analyzed during four weeks of a continuous enrichment of structural chernozem soil samples with a 0.1% solution of carboxymethyl cellulose (CMC) under aerobic and semianaerobic conditions. During the first 14 d, the total amount of the aerobic and anaerobic, cellulose-degrading microorganisms increased significantly. Various metabolic pathways were u‘ed te decompose the substrate: diverse metabolic systems were activated and different groups of microorganisms preferred in dependence on the presence of oxygen or the source of mineral nitrogen. In the later phases of cultivation, a decrease in the concentration of zymogenous microflora and in the level of substrate mineralization was observed ovon though CM-cellulase activity remained high. During the fourth week of cultivation, a conspicuous increase in the numbers of oligothropic bacteria occurring in the colcnies of the microorganisms degrading cellulose was found. The representatives of prosthecobacteria (Caulobacter, Hyphomicrobium, Prosthecomicrobium spp.) andSeliberia sp. were thus identified. This “microflora of dispersion” attends the zymogenous microbes degrading CMC and indicates later phases of the process of decomposition.     

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.