Fatty Acid Composition of Rhodococcus aetherivorans Cells During Phenol Assimilation

Abstract

The ability of microorganisms to survive in unfavorable conditions and maintain their biodegradation activity is mainly associated with changes in the composition of their cellular lipids. One of the factors of negative impact on cells can be their interaction with petroleum hydrocarbons, especially monoaromatic compounds, which are toxic to microorganisms even in small amounts. Aim. To research the changes in the cell fatty acids composition of Rhodococcus aetherivorans UCM Ac-602 strain during phenol degradation. Methods. The cultivation of the strain was carried out in a liquid mineral medium with initial phenol concentration 0.75, 1.0 and 1.5 g/L as a sole carbon and energy source. Cells grown in medium with n-hexadecane (7.5 g/L) and glucose (5.0 g/L) were used as controls. Fatty acid methyl esters were obtained by hydrolysis of cells in a 5% solution of acetyl chloride in methanol, followed by extraction with a mixture of ether-hexane. Identification of methyl esters was performed using a gas chromatography-mass spectrometry system Agilent 6800N/5973 inert (Agilent Technologies, US). The fatty acid content was determined using AgilentChemStation software. Results. Among the cellular fatty acids of R. aetherivorans UCM Ac-602 the straight-chain saturated hexadecanoic (C16:0), unsaturated hexadecenoic (C16:1 cis-9) and octadecenoic (C18:1 cis-9) acids as well as branched 10-methyl octadecanoic (tuberculostearic) (10-Me-C18:0) acid were dominated during growth on phenol and glucose. While in n-hexadecane grown cells main components of fatty acids pool were saturated tetradecanoic (C14:0) and hexadecanoic (C16:0) and unsaturated hexadecenoic (C16:1 cis-9) acids. The quantitative ratio of individual fatty acids of R. aetherivorans UCM Ac-602 cells differed depending on the substrate and incubation time. Under the influence of high phenol concentrations (1.5 g/L) there was a threefold increase in the ratio of straight-chain saturated to unsaturated fatty acids in comparison to cells grown on glucose and double increase compared to those grown on n-hexadecane. The amounts of 10-Мe-C18:0 fatty acid in cells grown on phenol were 1.8–3.2-fold higher in comparison to cells grown on glucose and 38.3–60.3-fold higher compared to those grown on n-hexadecane. In addition, the content of this acid in cells increased with increasing the time of incubation on phenol. Conclusions. A significant increase in the ratio of straightchain saturated to unsaturated fatty acids in the cells of R. aetherivorans UCM Ac-602 strain during growth on phenol and n-hexadecane in comparison to cells grown on glucose, as well as significant increase of methyl-branched (10-Me-C18:0) acid amount in phenol grown cells indicates the possible involvement of these fatty acids in the adaptation of the strain to the assimilation of toxic substances.