Basic studies on a new sugar-tolerant yeast.
Creators: name: Osman, Farouk Ahmed Ahmed
Publisher: name: University of Utah
Year: 2012
Subjects: Yeast
Nitrogen Fixation

description: 1. An osmohilic yeast strain was isolated from sugar syrup samples of high yeast count.  The taxonomic characteristics of this yeast strain were determined.  These characteristics showed that it is a new species of the genus Saccharomyces.   2. A series of experiments was conducted to investigate the ability of this yeast strain to fix atmospheric nitrogen.  The studies showed that in yeast cultures there was a decrease in total nitrogen, particularly in the first two hours of incubation.  In this series of experiments, only one experimental yeast culture showed and increase in total nitrogen.  Therefore, the ability of the yeast cells to fix atmospheric nitrogen was ruled out.  3.  The role of cations and anions in enhancing growth and possibly stimulating nitrogen-fixation by yeast cells was studied. The cations and anions tested were iron as ferrous sulfate, citrate as sodium citrate, phosphorus as K2HPO4, molybdenum as Na2MoO4.2H20, boron as boric acid and calcium as calcium chloride.  These trace elements did not stimulate the fixation of atmospheric nitrogen.  The only established effect of these cations and anions was the enhancement of yeast growth as indicated by an increase in the biomass.  Phosphorus enhanced the growth more efficiently than the other anions and cations tested.  On the other had citrate did not enhance the yeast growth to a significant degree.  4.  The effect of sucrose concentration on yeast growth was investigated.  It was found that the yeast cells grew well in lower sugar concentrations in the first 24 hours of incubation.  After that period, they grew more efficiently at higher sugar concentrations.  These findings indicated that this is an osmophilic strain. 5.  Studies of the effect of temperature on yeast culture growth indicated that the yeast cells were unable to grow at refrigerator temperature or a 56°C and they grew poorly at 37°C.  On the other had there was very good growth of yeast cells when incubated at room temperature (26°C).  6.  The effect of hydrogen-ion concentration on yeast growth was studied. It was shown that the yeast cells were able to grow over a wide pH range of 3 to 7 in Mycophil broth containing either 2 per cent or 30 per cent sucrose.  7. The efficiency of the utilization of various amino acids and ammonium sulfate as nitrogen sources by these osmophilic yeasts was studied.  The studied indicated that ammonium sulfate was utilized more efficiently than the other nitrogen sources tested.  At the same time some of the amino acids investigated such as proline, alanine, threonine and aspartic acid sustained growth better than L-glutamic acid and DL-methionine.  It was also found that the growth of 2 per cent sucrose was better than in 30 per cent sucrose during the nine hours incubation period.  No experiments of longer during were carried out.  8.  A survey of the free amino acids synthesized by the yeast cells cultured in Mycophil broth containing 30 per cent sucrose was made using unidirectional paper chromatography.  The solvents applied were butanol-acetic acid-water mixture and phenol.  The identified amino acids were L-glutamic acid, L-aspartic acid, DL-histidine, L-tyrosine, L-valine, L-leucine, L-glycine and L-lysine.  9.  Investigation of the effect of growth media on the free amino acid pool composition mentioned above was carried out.  Besides the Mycophil broth medium, two other media were used.  One was Mycophil broth containing no sucrose and the other was 30 per cent sucrose containing no other nitrogen source.  This investigation showed that most of the free amino acids identified as members of amino acid pool when cultured in Mycophil broth containing 30 per cent sucrose were found to be present in the pools of the yeast cells cultured in the other two media.  Tyrosine was the only amino acid which could not be identified as a member of the free amino acids identified in the yeast cells cultures in the three media mentioned above.  It was found that the content of L-glutamic acid, L-aspartic acid and DL-histidine was not significantly affected by differences in culture media.  The total level of the free amino acids identified as members of the amino acid pool grown in nitrogen-free medium, i.e., 30 per cent sucrose, was lowered.  It was also found that the level of lysine was significantly decreased in the case of yeast cells grown in Mycophil broth containing no sugar