Lipid and Elemental Composition as Indicators of the Physiological State of Sporangiospores in Mucor hiemalis Cultures of Different Ages

摘要

The number of sporangiospores used as inocula may significantly affect the development of the morphogenetic programs in mucoraceous fungi, including manifestations of dimorphism. In order to assess the physiological state of sporangiospores differing in their viability and germination patterns, lipid composition of sporangiospores from 6-, 14-, and 20-day cultures of Mucor hiemalis F-1431 was determined and the element ratios in these spores (Ca/K and P/S) were measured using X-ray microanalysis. While the lipid composition of the "old" (20 days) and "young" (6 days) spores was generally similar, older spores contained no cerebrosides, had half the level of polar lipids and γ-linolenic acid, and also contained 6 times more monoacylglycerols and 2.5 times more phosphatidic acid. The ratio of esterified to free sterols (ES/FS) characterizing the sterol storage pool was lowest in the spores from 20-day cultures. X-ray microanalysis revealed the highest P/S ratio in 6-day spores and lowest ratio in 14-day ones. Mature 14-day spores had the highest Ca/K ratio, ten times exceeding that for the 20-day spores. Higher values of P/S and Ca/K ratios in young (ripening) spores than in old 20-day spores indicate their higher metabolic activity and correlate with their higher viability and mycelial type of germination. Together with the lipid characteristics, the Ca/K and P/S ratios are the parameters which may be used to develop the criteria for assessment of the physiological state of the cells, including viable fungal sporangiospores. This complex may be also used to assess the capacity of mucoraceous fungi for dimorphism, including the species (M. hiemalis) for which this capacity has not been demonstrated previously.