Oxylipins in automictic yeast life cycles

[摘要] English: 3-OH oxylipins are saturated and unsaturated oxidized fatty acids which are produced in mitochondria via incomplete b-oxidation or fatty acid synthesis type II. These compounds possibly play an important role in the sexual cycle of yeasts by assisting with ascospore liberation. Literature suggests that 3-OH oxylipins act as a lubricant during ascospore liberation, thereby ensuring efficient release of ascospores. Since the discovery of oxylipins i.e. 3-hydroxy (OH) oxylipins in the early 1990's, these compounds were found to be distributed in various species of the fungal domain. Studies performed thus far, however, focused mainly on non-fermenting yeast species such as Ascoidea, Dipodascopsis and Eremothecium. According to various studies performed so far, 3-OH oxylipins were found to accumulate specifically in the sexual structures (asci and surrounding ascospores) of various nonfermenting yeasts. These studies also revealed that the sexual stages of nonfermenting yeasts are most susceptible to acetylsalicylic acid (ASA), a known mitochondrial (respiration and 3-OH oxylipin production) inhibitor. No information regarding oxylipin accumulation in asci or ASA-sensitivity of fermentative yeasts, however, has so far been reported. Using confocal laser scanning microscopy in combination with an oxylipin probe for 3-OH oxylipins and coupled to a fluorescing secondary antibody, the accumulation of these oxylipins was discovered in the asci of the following fermentative yeasts i.e. Pichia anomala, Pichia farinosa and Schizosaccharomyces octosporus. Interestingly, no 3-OH oxylipin accumulation was observed in the asci of the fermenting yeast Zygosaccharomyces bailii. This could be ascribed to the fact that this yeast depends more on a fermentative pathway for growth and sexual reproduction, than on mitochondrial respiration. Since 3-OH oxylipins are produced in the mitochondria, it is expected that there should be an increase in mitochondrial activity associated with these sexual structures. Using confocal laser scanning microscopy and a mitochondrial fluorescing probe (Rhodamine 123), an increase in mitochondrial activity was also observed in the asci of the fermenting yeasts tested, again with the exception of Z. bailii. Furthermore, during this study links between yeast sexual reproduction, 3-OH oxylipin accumulation/production, mitochondrial activity and oxygen requirement were established. This study revealed that fermenting yeasts are more resistant to ASA than non-fermenting yeasts when grown in liquid media. This is probably due to the fact that these yeasts can use either aerobic respiration or a fermentative pathway for growth and reproduction. This research prompted the development of a bio-assay that may find application in screening for effective antimitochondrial antifungals.

[发布机构] University of the Free State