V.K. Eroshin

Arachidonic acid production by Mortierella alpina with growth-coupled lipid synthesis

Abstract The fungus Mortierella alpina LPM 301, a producer of arachidonic acid (ARA), was found to possess a unique property of a growth-coupled lipid synthesis. An increase in specific growth rate (μ) from 0.03 to 0.05 h−1 resulted in a two-fold increase in the specific rate of lipid synthesis (milligram lipid (gram per lipid-free biomass) per hour). Under batch cultivation in glucose-containing media with urea or potassium nitrate as nitrogen sources, the ARA content was 46.0 and 60.4% of lipid; 16.4 and 18.8% of dry biomass; and 4.2 and 4.5 g l−1, respectively. Under continuous cultivation of the strain, the productivity of ARA synthesis was 16.2 and 19.2 mg l−1 h−1 at μ=0.05 and 0.03 h−1, respectively.

[Growth-coupled lipid synthesis in Mortierella alpina LPM 301, a producer of arachidonic acid].

Mortierella alpina LPM 301, a producer of arachidonic acid (ARA), was found to possess a unique property of intense lipid synthesis in the period of active mycelium growth. Under batch cultivation of this strain in glucose-containing media with potassium nitrate or urea, the bulk of lipids (28–35% of dry biomass) was produced at the end of the exponential growth phase and remained almost unaltered in the stationary phase. The ARA content of lipids comprised 42–50% at the beginning of the stationary phase and increased continuously after glucose depletion in the medium due to the turnover of intracellular fatty acids; by the end of fermentation (189–210 h), the amount of ARA reached 46–60% of the total fatty acids (16–19% of dry mycelium). Plausible regulatory mechanisms of the growth-coupled lipid synthesis in microorganisms are discussed.

The effect of two inhibiting substrates on growth kinetics and cell maintenance of the yeast Candida valida

The biomass yield, YX/S, and the specific growth rate, μ, of the ethanol-utilising yeast Candida valida was studied over a wide range of concentrations of two substrates, ethanol and zinc. The experimental results suggested that the cell maintenance rate, mS, was affected by each. Ethanol at high concentrations exerted substrate inhibition on the culture growth, which was manifested as a decrease of ethanol consumption rate and an increase of mS. A sharp increase of mS was observed at very low and high zinc concentrations, which might be a result of energy expenditure on zinc transport. The dependencies of biomass yield on specific growth rate during the variation of ethanol and zinc concentrations were two-branched, that for ethanol having the shape of a loop. A mathematical model of the cultures has been developed which is in good agreement with the experimental data.

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.

Water-soluble immunomodulator produced by Trichosporon pullulans yeast

Abstract An extracellular glycoprotein exhibiting immune activity was produced by Trichosporon pullulans yeast grown in a defined ethanol-containing medium. The glycoprotein had a molecular mass of 100–150 kDa. The carbohydrate portion of the glycoprotein consisted of mannose as a predominant component, glucose, and a small amount of arabinose. This glycoprotein was named MAG. Immunological studies showed that MAG exhibited a high immunomodulating activity, revealed distinct adjuvant properties, had a wide therapeutic index, and increased non-specific resistance of mammals to infection. In batch culture, the most active MAG production (36·4 mgl 1 ) coincided with the phase of active yeast growth. In a chemostat under nitrogen limitation, the rate of the MAG synthesis increased with increasing a specific growth rate.