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Biomedical subjects

A M Semenov

Publications and source records attributed to A M Semenov.

12 recordsLinked to original sources
PubMed2005

Short-term wavelike dynamics of bacterial populations in response to nutrient input from fresh plant residues.

The objectives of the research were to investigate short-term dynamics of bacterial populations in soil after a disturbance in the form of fresh organic matter incorporation and to investigate how these dynamics are linked to those of some environmental parameters. To reach these objectives, soil bacterial populations, mineral nitrogen, pH, and redox potential (ROP) were monitored daily for 1 month after incorporation of clover-grass (CG) plant material in microcosm experiments. Colony-forming units (CFUs) and direct microscopic counts of FDA-stained and FTTC-stained bacteria increased immediately after incorporation of the plant material, dropped within 2 days, and fluctuated thereafter. Harmonics analysis demonstrated that there were significant wavelike fluctuations with three or four significant peaks within 1 month after incorporation of clover-grass material. Peaks in CFUs were 1-2 days ahead of those in direct counts. Ammonium (NH4) concentrations increased from the start of the experiments until nitrification commenced. Nitrate (NO3) concentrations dropped immediately after plant incorporation, and then rose monotonically until the end of the experiments. There were no wavelike fluctuations in NH4 and NO3 concentrations, so that bacterial fluctuations could not be attributed to alternating mineral N shortages and sufficiencies. pH levels rose and declined with NH4 levels. ROP dropped shortly before NH4 concentrations rose, and increased before NH4 concentrations decreased; there were no regular fluctuations in ROP, so that temporary oxygen shortages may not have been responsible for the observed fluctuations in bacterial populations. Thus, for the first time, regular wavelike dynamics were demonstrated for bacterial populations after perturbation by addition of fresh organic matter to soil, and several potential reasons for the death phase of the fluctuations could be excluded from further consideration.

Bacteria↗
PubMed2002

Wavelike distributions of infections by an introduced and naturally occurring root pathogen along wheat roots.

Previously, we showed that copiotrophic and oligotrophic bacteria fluctuate as moving waves along roots. These waves probably originate as a result of growth and death cycles at any location where a moving nutrient source passed. In this study, we placed sclerotia of Rhizoctonia solani AG8 along growing roots of wheat and showed that the proportions of root sections from which R. solani was isolated fluctuated with distance from the root tip. Similarly, proportions of root sections from which naturally occurring Pythium spp. were isolated fluctuated with distance from the root tip. Fourier analysis showed that these fluctuations constituted significant waves. Cross-correlation analyses demonstrated that there were negative correlations between R. solani infections and colony forming units of copiotrophic bacteria at the time of inoculation at the same locations on the root (lag = 0 cm), indicating that infection by R. solani could have been inhibited by these bacteria. There was a positive correlation between Pythium infections and copiotrophic bacteria at a lag of 6 cm along the roots. It therefore appears that Pythium infection took place shortly after the initial peak in copiotrophic bacteria following the passage of the root tip.

Colony Count, Microbial↗
PubMedDate not supplied

[Inhibition of the growth of Candida utilis by certain heavy metals].

The effect of Zn2+, Mn2+, Cd2+ and Hg2+ ions on the kinetics of growth was studied with Candida utilis. The inhibition of Candida utilis growth by Zn2+ and Mn2+ ions is described by the equation for noncompetitive inhibition of enzymatic reactions which is not the case with Cd2+ and Hg2+ ions. The inhibition constants (Ki) for these metals have been determined.

Cadmium↗
PubMedDate not supplied

[Effect of zinc ions on Candida utilis].

The effect of zinc on the growth of Candida utilis was studied as well as on the rates of RNA and protein synthesis, and the uptake of zinc ions by the cells. The kinetics of C. utilis growth inhibition by zinc ions can be described by the equation for noncompetitive inhibition of enzymatic reactions. The uptake of zinc is a two-phase process. Zinc ions are adsorbed by the surface of the cell at the first phase, and are actively transported inside the cell at the second phase. Protein synthesis is suppressed by zinc ions more than RNA synthesis. Apparently protein synthesis is most sensitive to zinc among other metabolic processes and its inhibition caused deceleration of growth and then death of cells.

Candida↗
PubMedDate not supplied

[Adaptation of Candida tropicalis yeasts to increasing hydroquinone concentrations].

The optimal concentration of hydroquinone in the Rieder medium for Candida tropicalis is 0.2 to 0.25%. This yeast is capable of growing in a medium containing up to 0.7-0.9% of hydroquinone. C. tropicalis cultures capable of growing in the Rieder medium containing 2.5% of hydroquinone have been obtained by the method of experimental adaptation. Comparative studies of yeast cultures adapted to 0.5 and 1.5% of hydroquinone have shown that the lag period in the batch culture decreases noticeably as the result of adaptation. The coloured products of hydroquinone transformation are not accumulated any more in the cultural broth and the cells. The generation time of the yeast is the same during cultivation on 0.2 and 0.5% hydroquinone but differs if the content of hydroquinone in the medium is 1%. No increase in the economic coefficient has been found during cultivation of the yeast cultures adapted to 1.5% hydroquinone in media containing 0.2 and 0.5% of hydroquinone, although the activity of phenol monooxygenase increased. The latter peculiarity of the adapted cultures was most pronounced during cultivation in media containing 0.5 to 1% of hydroquinone. No changes have been detected in the regulation mechanisms for biosynthesis of phenol monooxygenase or in the resistance of the enzyme to the substrate and the products of its spontaneous oxidation.

Adaptation, Physiological↗