I. G. Minkevich

The effect of lipid content on the elemental composition and energy capacity of yeast biomass.

Oleaginous yeasts (18 strains) were grown in ethanol media under various cultivation conditions (33 biomass samples). It was found that lipid and lipid-free fractions of dry biomass have elemental composition and biomass reductivity very close to values which can be considered as biological constants. The energy content of dry biomass strongly depended on the total lipid content. When the lipid content was 64%, the energy value of dry biomass reached 73% of diesel oil; therefore, oleaginous microorganisms can be a promising source of biodiesel fuel. The approach used in this work makes it possible to determine the energy value of biomass by its elemental composition without application of laborious and expensive calorimetric measurements of combustion heats.

Kinetic characteristics of metal-EDTA degradation by immobilised cells of bacterial strain DSM 9103

Abstract A biosensor approach was applied to study the degradation of ethylenediaminetetraacetate (EDTA) and metal–EDTA complexes with Mg 2+ , Mn 2+ , Ba 2+ , and Ca 2+ by bacterial cells of strain DSM 9103 immobilised by sorption on Whatman GF/A chromatographic paper. Kinetic characteristics of EDTA degradation: maximum rate of oxygen consumption ( V max ), saturation constant ( K s ), and inhibitory constant ( K i ) were determined from the measured values of oxygen consumption rate at different substrate concentrations. Values of V max for all the substrates studied were similar whereas the values of K s and K i differed considerably. Uncomplexed EDTA and Ca–EDTA had the highest affinity to the EDTA-degrading system; Mn–EDTA showed the highest inhibitory effect. Results obtained offer considerable scope for the development of microbial biosensors sensitive to extremely low concentrations (5–100 μM) of EDTA.

Bacterial Degradation of EDTA

Degradation of EDTA (ethylenediaminetetraacetic acid) or metal–EDTA complexes by cell suspensions of the bacterial strain DSM 9103 was studied. The activity of EDTA degradation was the highest in the phase of active cell growth and decreased considerably in the stationary phase, after substrate depletion in the medium. Exponential-phase cells were incubated in HEPES buffer (pH 7.0) with 1 mM of uncomplexed EDTA or EDTA complexes with Mg2+, Ca2+, Mn2+, Pb2+, Co2+, Cd2+, Zn2+, Cu2+, or Fe3+. The metal–EDTA complexes (Me–EDTA) studied could be divided into three groups according to their degradability. EDTA complexes with stability constants K below 1016 (log K < 16), such as Mg–EDTA, Ca–EDTA, and Mn–EDTA, as well as uncomplexed EDTA, were degraded by the cell suspensions at a constant rate to completion within 5–10 h of incubation. Me–EDTA complexes with log K above 16 (Zn–EDTA, Co–EDTA, Pb–EDTA, and Cu–EDTA) were not completely degraded during a 24-h incubation, which was possibly due to the toxic effect of the metal ions released. No degradation of Cd–EDTA or Fe(III)–EDTA by cell suspensions of strain DSM 9103 was observed under the conditions studied.

Degradation of EDTA by a chemostat culture of bacterial strain DSM 9103

Abstract Characteristics of growth and EDTA degradation by chemostat culture of bacterial strain DSM 9103 were investigated. The effect of specific growth rate ( μ ) on mass cell yield ( Y X/S ), specific rate of EDTA uptake ( q S ) and the rate of Mg–EDTA degradation by a cell suspension ( q S rest ) was studied. Based on the experimental data, kinetic constants of dependencies q S ( S ) and μ ( S ) were determined. The rates of substrate and energy expenditures for cell maintenance, m S and m e , were 0.02 and 0.014 h −1 , respectively. High efficiency of DSM 9103 growth on EDTA in a chemostat was established; the maximum mass cell yield ( Y X/S m ) and the maximum energy cell yield ( η X/S m ) were as high as 35.3 and 50.5%, respectively. Results indicated that oxidation of side chains in the EDTA molecule by monooxygenase is coupled with energy utilization by the cells. Cells harvested from a chemostat (resting cells) retain the capability of EDTA degradation, although at a rate about four to five times lower than growing cells.

The effect of pH, aeration, and temperature on arachidonic acid synthesis by Mortierella alpina

The effects of pH, aeration, and temperature on the growth of fungal strain Mortierella alpina LPM-301 and the synthesis of lipids and arachidonic acid in glycerol-containing medium were studied. Arachidonic acid production in the stationary growth phase was found to depend considerably on the pH value; it reached the optimum at pH 6.0 and was irreversibly inhibited at a pH of 3.0. The pO2 values in a range from 10 to 50% showed no marked effect on mycelium growth or the synthesis of lipids and arachidonic acid. The temperature optimum for arachidonic acid production was 20–22°C. Under continuous cultivation, the amount of arachidonic acid reached 29.8% of lipids and 7.4% of biomass. The arachidonic acid yield from the glycerol consumed was 4.1% by mass and 8.8% by energy. It is suggested that arachidonic acid synthesis at an unfavorable pH and elevated temperatures was limited by the activity of Δ-12-desaturase and by the conversion of linoleic to arachidonic acid, respectively.

Theoretical and experimental quantum efficiencies of the growth of anoxygenic phototrophic bacteria

Abstract This work is devoted to investigation of regularities of mass–energy balance of purple bacteria photorophic growth. Estimates of culture growth efficiency were derived from bioenergetic properties of cell metabolism. An equation system describing joint balance of flows of metabolite reductivity, high-energy protons (HEP) and high-energy bonds (HEB) was formulated. The maximum cell yield from light and the rate of energy expenditure for cell maintenance were found as mathematical expressions containing metabolic stoichiometric coefficients, rates of energy losses and intracellular matter turnover. Experimental study was conducted with a purple bacterium Rhodobacter capsulatus grown continuously on hydrogen at different illumination intensities. The obtained numerical estimates of attainable maximum growth yield were compared with experimental data both taken from literature and obtained in this work. Theoretical and experimental yield values showed good agreement.

Growth of the thermotolerant yeast, Candida valida, on ethanol: Dependences of maximal growth rate and cell biomass yield on temperature

SummaryGrowth of Candida valida on ethanol in pH-auxostat and chemostat has been studied. Maximal growth rate, μm, and cell biomass yield, Ys, display the Arrhenius dependence on temperature within the ranges 18°–30° C and 30°–36° C and an abrupt fall above 36° C. The temprature dependence of both parameters has breaks at 30° C and 36° C. Activation energies have been measured for both μm and Ys. The reason for a weaker effect of temperature on Ys than on μm is discussed.

EDTA-dependent assimilation of glucose and organic acids by an EDTA-degrading bacterium

Bacterial strain VKM B-2445 is characterized by ethylenediaminetetraacetate (EDTA) requirement for cell growth. This strain could not grow on glucose and organic acids as the sole sources of carbon and energy, but it was able to metabolize these substrates added to EDTA medium. EDTA initiated assimilation of glucose, succinate, fumarate, malate, and citrate and supplied nitrogen for the biomass production from these substrates. Utilization of primarily nongrowth substrates by strain VKM B-2445 started when EDTA was exhausted or at least considerably degraded.

The stoichiometry and energetics of oxygenic phototrophic growth

The values of gross metabolic flows in cells are essentially interconnected due to conservation laws of chemical elements and interrelations of biochemical coupling. Therefore, the overall stoichiometry of cellular metabolism, such as the biomass quantum yield, the ratio between linear and circular flows via the electron transport chain, etc., can be calculated using balances of metabolic flows in the network branching points and coupling ratios related to ATP formation and expenditures. This work has studied the energetic stoichiometry of photosynthetic cells by considering the transfer of reductivity in the course of biochemical reactions. This approach yielded rigorous mathematical expressions for biomass quantum yield and other integral bioenergetic indices of cellular growth as functions of ATP balance parameters. The effect of cellular substance turnover has been taken into account. The obtained theoretical estimation of biomass quantum yield is rather close to experimental data which confirms the predictive capacity of this approach.