Effects of a first exposure to ethanol on the compositions of neutral and polar lipids in Euglena gracilis Z, taken as a hepatic cell model: equilibration by citrulline-malate

Fatty Acid Accumulations and Transcriptome Analyses Under Different Treatments in a Model Microalga Euglena gracilis

With the continuous growth of the world’s population and the increasing development of industrialization, the demand for energy by human beings has been expanding, resulting in an increasingly severe energy crisis. Microalgae are considered the most potential alternatives to traditional fossil fuels due to their many advantages, like fast growth rate, strong carbon sequestration capacity, and low growth environment requirements. Euglena can use carbon sources such as glucose, ethanol, and others for heterotrophic growth. Moreover, Euglena is highly adaptable to the environment and has a high tolerance to various environmental stresses, such as salinity, heavy metals, antibiotics, etc. Different treatments of Euglena cells could affect their growth and the accumulation of bioactive substances, especially fatty acids. To expand the industrial application of Euglena as a potential biodiesel candidate, we determine the physiological responses of Euglena against environmental stresses (antibiotics, heavy metals, salinity) or carbon resources (glucose and ethanol), and evaluate the potential for higher quality and yield of fatty acid with a high growth rate. Adding glucose into the culture media increases cell biomass and fatty acid production with high-quality biodiesel characters. The transcriptome analysis helped explore the possible regulation and biosynthesis of fatty acids under different treatments and exploited in the improvement of biodiesel production. This study provides insights for further improvement and various culture treatments for Euglena-based biodiesel and jet fuels.

Evaluation of Euglena gracilis 815 as a New Candidate for Biodiesel Production

Euglena comprises over 200 species, of which Euglena gracilis is a model organism with a relatively high fatty acid content, making it an excellent potential source of biodiesel. This study isolated and characterized a new strain named E. gracilis 815. E. gracilis 815 cells were cultivated under light and dark conditions, with either ethanol or glucose as an external carbon source and an autotrophic medium as control. To achieve maximum active substances within a short period i.e., 6 days, the effects of the light condition and carbon source on the accumulation of bioactive ingredients of E. gracilis 815 were explored, especially fatty acids. In comparison with the industrially used E. gracilis Z strain, E. gracilis 815 exhibited high adaptability to different carbon sources and light conditions, with a comparable biomass and lipid yield. The content and composition of fatty acids of E. gracilis 815 were further determined to assess its potential for biodiesel use. Results suggested that E. gracilis 815 has biodiesel potential under glucose addition in dark culture conditions and could be a promising source for producing unsaturated fatty acids. Therefore, E. gracilis 815 is a candidate for short-chain jet fuel, with prospects for a wide variety of applications.

A fatty-acid synthesis mechanism specialized for parasitism

Most cells use either a type I or type II synthase to make fatty acids. Trypanosoma brucei, the sleeping sickness parasite, provides the first example of a third mechanism for this process. Trypanosomes use microsomal elongases to synthesize fatty acids de novo, whereas other cells use elongases to make long-chain fatty acids even longer. The modular nature of the pathway allows synthesis of different fatty-acid end products, which have important roles in trypanosome biology. Indeed, this newly discovered mechanism seems ideally suited for the parasitic lifestyle.

Presence of proteins recognized by mammalian cytochrome P-450 antibodies in Euglena gracilis

We have attempted to probe three microsomal cytochrome P-450 isozymes in Euglena gracilis using immunochemical methods. They cross-react with anti-rat cytochrome P4502C11, cytochrome P4502E, and cytochrome P4502B. Activities of alkoxyphenoxazone dealkylation have been tested in living cells. In untreated cultures, the amount of proteins recognized by anti-cytochrome P4502C11 or anti-cytochrome P4502E is high. Phenobarbital treatment increased the levels of microsomal proteins recognized by antibody to cytochrome P4502B, as well as dealkylases of pentoxyresorufin, but decreased the level of proteins recognized by anti-cytochrome P450C11 or cytochrome P4502E. These results suggest that these unicellular algae may contain different isozymes of microsomal cytochromes P-450, comparable to those in mammalian liver. They are cytochrome P-450 equivalents of mammalian isoenzymes 2C, 2E and 2B. However, we could not demonstrate ethanol induction of cytochrome P-450 equivalent to isoenzyme 2E. Its role in xeno- or endobiotic metabolism remains to be elucidated.

Microsomal ethanol-oxidizing system in Euglena gracilis. Similarities between Euglena and mammalian cell systems

1. ADH activity of Euglena grown with 50 mM ethanol decreased, but MEOS activity increased with a corresponding increase in the total amount of cytochrome P-450. 2. Phenobarbital treatment increased the total amount of cytochrome P-450. 3. CO and KCN, cytochrome P-450 ligands, diminished acetaldehyde formed from ethanol oxidation by MEOS. 4. The amounts of NAD(P)H cytochrome c reductases and cytochrome b5 type, components of microsomal monooxygenase reaction, have been spectrophotometrically measured. 5. NAD(P)H cytochrome c reductases activities were induced by phenobarbital. 6. DMSO, an inhibitor of rabbit MEOS, inhibited O2 consumption (11-20%) by Euglena grown with an ethanol, but not a lactate medium. 7. These studies indicate the presence of cytochrome P-450-dependent MEOS in Euglena similar to that in the mammalian hepatic cell.

Use of a microbial model for the determination of drug effects on cell metabolism and energetics: study of citrulline-malate

Euglena gracilis can be used as a microbial model to study the effect of drugs on lactate metabolism and gluconeogenetic synthesis. The cell growth and metabolism have been characterized in a 33 mM lactate medium, non-supplemented or supplemented by dl-malate or by l-citrulline alone or by the compound formed by the stoichiometric combination of the two components: the citrulline-malate (Stimol). The malate of the complex accelerated the ammonium disappearance, while the citrulline facilitated the lactate consumption. A synergistic action of the complex, by comparison with the additive effects of the individual components, on most of the parameters studied was detected. A remarkable resistance to anoxia, and a quicker recovery under aeration of the cells supplemented with CM, were evident: after carbonation for 2 min the total nucleotides in the medium were increased by 44 per cent with an unchanged energy charge; and after a prolonged (20 min) anoxia followed by an aeration, the capacities of the cells to synthesize ATP in the presence of excesses of both ADP and phosphate were two-fold higher in Stimol treated cells than in control.

Citrulline-malate effect on microsome phospholipids and cytochrome P450 in Euglena grown with ethanol

This study indicates for the first time the presence of cytochrome P450 in the microsomes of Euglena grown in lactate medium and substantiates the use of Euglena as a hepatic cell model. Similar effects of ethanol on Euglena and on rat hepatic microsomes were demonstrated: (i) decrements in the quantities of FA per milligram of proteins; (ii) increases in the proportions of PE; (iii) decreases in the proportions of PC; and (iv) production of cytochrome P450, degraded in P420. The citrulline-malate reestablishes in the microsomes the phospholipid environment and the cytochrome P450 concentration. These findings illustrate that the complex acts on the lipid peroxidation via the changes in cytochrome P450 activity.