Some yeasts produce sexual spores (ascospores) in a variety of shapes and surface
ornamentations. These intriguing structures have hitherto been used only in yeast
classification. In this study the likely primary function of ascospore shape and
ornamentations with associated lipids in water-driven movement as aiding the
dispersal of ascospores from enclosed containers (asci), is proposed. This
interpretation might find application in nano-, aero- and hydro -technologies with the
re-scaling of these structures. Through sexual reproduction, some yeasts produce
microscopic containers (asci) that enclose ascospores of many different shapes and
various nano-scale surface ornamentations. Some spores are spherical with an
equatorial ledge (like the planet Saturn), or resemble hats with a bole and brim, while
others look like corkscrews, walnuts, spindles with whip-like appendages, needles,
and hairy or warty balls. Until now, these structures were used to classify yeasts and
little thought was apparently given to their possible functional role. From literature
and microscopic observations, it was found that the yeasts Dipodascopsis
uninucleata and Dipodascus have evolved sophisticated means that enable the
dispersal of oxylipin-coated spherical and bean-shaped spores from bottle-shaped
containers (asci) without inverting or shaking them. Here, spores are pushed by
turgor pressure towards the narrow opening and then ejected. Studies of
Dipodascopsis suggest that oxylipin-coated, interlocked hooked ridges on the
surfaces and stretching across the length of bean- to ellipsoidal-shaped spores are responsible for the alignment of the latter. Here, spores inside the container are
positioned side-by-side in a column of linked clusters with elongated sides attached
by interlocking hooked ridges in gear-like fashion and orientated mainly with one end
towards the opening. It was concluded that hooked ridges form turbine-like structures
at both ends, causing propeller-like rotation when the spores are pushed by water
pressure towards the ascus opening. This rotational movement loosens the spores
(by the unlocking the hooked-ridges) near the container neck, which is necessary for
sliding past each other for eventual release. Eventually, spores are released
individually from the bottle-shaped ascus while rotating at about 1200 rpm at
approximately 110 length replacements per second. With some species of the genus
Dipodascus, compressible oxylipin-coated sheathed surface structures and not gears
are used to separate and loosen spherical spores in a similar bottle -shaped container
before individual release under turgor pressure. These spores simply slide past each
other when pressed towards the opening. It is presumed that more complex
mechanics are needed to allow the effective release of bean- to ellipsoidal-shaped
ascospores compared to spherical sheathed ascospores, for which alignment and
rotation are unnecessary. Using gas chromatography-mass spectrometry, it was
discovered that a saturated 3-OH 14:0 (mass fragments:175 [CH3O(CO)-CH2-CHO-TMSi];
330 [M + ]; 315 [M + -15]) is produced by the yeast Eremothecium ashbyii. In
order to map the oxylipinâs location in the yeast, antibodies (against these oxylipins)
and immunofluorescence microscopy on cells in sexual mode was employed. The
oxylipin was present as part of a V-shaped structure on sickle-shaped spores. With
the aid of confocal laser scanning microscopy to observe cells treated with antibody
and fluorescine (FITC anti-rabbit IgG), it was concluded that the hydrophobic V-shaped
structure was present as a mirror image on both sides at the blunt end of an otherwise hydrophilic spore as indicated by differential ascospore staining. Scanning
electron microscopy showed this structure to be fin-like protuberances. Next, the
function of these fin-like structures and ascospore shape was addressed. Using
microscopy, it was discovered that spores are sometimes forced through the ascus
with the spiked tip rupturing the ascus wall. Water pressure caused a boomerang
movement when the blunt end is pushed forward with the spike leading the way in a
circular motion. This happens only when micron streams of water move across the
fins from the blunt end towards the tip of the spore. It is believed that this part of the
study has only scratched the surface of water-driven ascospore movement in yeasts
on a micrometer scale and that the mechanical implications of many spore shapes
with a large number of different hydroxy oxylipin-lubricated, nano-scale surface
ornamentations await similar explanation and elaboration. Why did some yeasts
evolve peculiar spore movement with the beneficial consequence, so far as we can
see, to escape from closed or partially closed containers? Of course, this should be
important from a survival point of view since without this ability, yeasts will probably
not be able to disperse properly. It is believed that if appropriate ultrastructural
studies (using glutadialdehyde and osmium tetroxide as fixatives) are conduc ted on
yeasts aimed at exposing ascospore surface ornamentations and not merely
membrane structure, conducted in the past, clues can be gained to reveal the
mechanics behind the motion of nano-sized particles in fluids. Consequently a further
aim of this study became to assess ascospore structure (using above ultrastructural
method) especially nano-scale ornamentations with associated lipids especially
oxylipins in various unrelated yeasts. These were obtained for the yeasts
Eremothecium sinecaudum (ascospores corkscrew-shaped and coated with
oxylipins), Dipodascopsis uninucleata var. wickerhamii (smooth surfaces without oxylipins), Lipomyces kononenkoae (smooth ascospore surface with lipid sacs), L.
tetrasporus (ridged ascospore surface with lipid sacs), Saturnispora saitoi (Saturn-shaped
ascospores covered with oxylipins), Ascoidea africana (hat-shaped
ascospores covered with oxylipins), Ambrosiozyma platypodis (double brimmed hat-shaped
ascospores), Nadsonia commutata (ascospore surface warty; cells contain
oxylipins) and N. fulvescens (ascospore surface hairy-like; cells contain oxylipins).
Interesting patterns regarding lipid turnover (i.e. total-, neutral-, phospho-, glycolipids
and associated fatty acids) were found when asexual and sexual stages of above
yeasts are compared.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-09302005-084339 |
| Date | 30 September 2005 |
| Creators | Bareetseng, Andries Sechaba |
| Contributors | Prof JLF Kock, Prof PWJ van Wyk, Dr CH Pohl |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-09302005-084339/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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