Influence of increased content of phosphates on the growth and pH of mixotrophic culture Euglena gracilis
Mokrosnop V.M.
M.G. Kholodny Institute of Botany, NAS of Ukraine
e-mail: vmokrosnop@gmail.com

	Annotation Cultivation of microalga E. gracilis in the presence of ethanol leads to the pH lowering of nutritional medium. Increasing of buffer capacity by adding additional amount of phosphates to the medium delays a rapid pH decreasing. Concentration of the cells in such cultures exceeds the control level on the 10-15%.  

	Euglena gracilis is a microalga that can grow in the presence of high concentrations of ethanol in the medium (Rodriguez-ZavalaJ. S. et. al., 2010). This organism uses ethanol as a source of carbon and energy due to the activity of two types of ethanol metabolizing enzymes: NAD-dependent alcohol and aldehyde dehydrogenases of cytosol and mitochondria (Yoval-Sanchez B. et. al., 2011). In the process of ethanol oxidation by algal cells a rapid decrease in the pH of the culture liquid was observed, which may be due to the release of acetate from the cells. A significant decrease in pH level has negative effect on the culture growth.
	Increasing of the phosphates (KH2PO4 and (NH4)2HPO4, 1:1) content in the E. gracilis culture medium can increase its buffer capacity and delay pH decreasing. In our experiments were used four variants of phosphates content in the saline nutritional medium Cramer and Myers: 2 (Control), 3, 4, 6 and 8 g/L. In all the variants was added ethanol (100 mM). The initial pH level of all variants was 7.0. During growth period of the culture E. gracilis was conducted measurement of pH and culture growth rate. 
	Decreasing of the pH level was observed in all variants, but with different time of its beginnings. Increasing in phosphate content up to 4 g/L delays decreasing pH to 3.0 to the 13-th day of cultivation, when in control variant pH level was 3.0 on the 7-th day. In the variants with phosphate content 6-8 g/L was not fixed pH below 4.0. Growth rate of the cultures was the highest on the 1-3-th days and then were decreasing. The highest growth rates in the period 1-7 days were in variants with phosphate content 3 and 4 g/L, but in the period 7-13 days in variants with 6 and 8 g/L. Cell concentration was maximal in all cultures on the 13-th day, and in relation to the control was the highest in variant with phosphate content 6 g/L. Addition of 6 and 8 g/L phosphates in the medium is favorable for increasing of cell concentration in the E. gracilis culture by 10-15% in comparative with control.