T. I. Chistyakova

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.

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.

Application of organic acids for plant protection against phytopathogens

The basic tendency in the field of plant protection concerns with reducing the use of pesticides and their replacement by environmentally acceptable biological preparations. The most promising approach to plant protection is application of microbial metabolites. In the last years, bactericidal, fungicidal, and nematodocidal activities were revealed for citric, succinic, α-ketoglutaric, palmitoleic, and other organic acids. It was shown that application of carboxylic acids resulted in acceleration of plant development and the yield increase. Of special interest is the use of arachidonic acid in very low concentrations as an inductor (elicitor) of protective functions in plants. The bottleneck in practical applications of these simple, nontoxic, and moderately priced preparations is the absence of industrial production of the mentioned organic acids of required quality since even small contaminations of synthetic preparations decrease their quality and make them dangerous for ecology and toxic for plants, animals, and human. This review gives a general conception on the use of organic acids for plant protection against the most dangerous pathogens and pests, as well as focuses on microbiological processes for production of these microbial metabolites of high quality from available, inexpensive, and renewable substrates.

Bacterial strain characterizing by EDTA requirement

A novel strain of bacteria (LPM-4) characterized by a unique EDTA requirement for cell growth was isolated. Suspensions of washed cells of strain LPM-4 degraded EDTA complexes with Ba2+, Mg2+, Ca2+, and Mn2+ at constant rates ( 0.310 ± 0.486 mmol EDTA/(g h)) and Zn-EDTA at an initial rate of 0.137 ± 0.016 mmol EDTA/(g h). The temperature optima for cell growth and EDTA degradation were determined under pH-auxostat cultivation. As compared with the known EDTA-degrading bacteria, strain LPM-4 exhibited a higher specific growth rate (0.095− 1) and lower mass cell yield (0.219 g cells/g EDTA), which is promising for its practical applications for EDTA removal in wastewater treatment plants.

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.