In view of the decline of natural habitats due to urban and industrial
development, the need to search for new yeasts is pressing since few natural
habitats have been thoroughly investigated for yeast species. Yeasts have
not been isolated from Lesotho before despite being an ideal environment for
yeasts. In addition, isolation of yeasts able to utilize complex substrates,
similar to intermediates in the degradation of chlorophenols would be
important in their detoxification. Yeasts with these abilities are usually
isolated from polluted environments and their presence from the pristine
environment in Lesotho would be unexpected.
The species Lipomyces starkeyi and L. tetrasporus were found distributed
throughout the various habitats while Debaryomyces hansenii, D. hansenii
var. fabryi and D. occidentalis were found in 60% - 70% of the different
regions. Debaryomyces polymorphus, Dipodascus spicifer, Galactomyces
geotrichum, G. reessii, Kluyveromyces lactis , L. kononenkoae, L.
mesembrius, L. spencermartinsiae, Pichia anomala, P. fabianii, P.
guilliermondii and Yarrowia lipolytica were site specific. The fatty acid profiles
of the isolated lipomycetous yeasts are similar to those reported in literature.
This corroborates the value of this phenotypic characteristic in the taxonomy
of these yeasts.
The PCR products of the ITS region of some of the type strains of the family
Lipomycetaceae showed high length variation enabling rapid identification.
The type strains, the sub-species and the varieties of the family
Lipomycetaceae could be differentiated from each other using RFLP profiles obtained with the restriction enzymes used in combination i.e. Cfo I, HaeIII and
MboI. The RFLP profiles for the five Lesotho isolates with atypical
carbohydrate patterns could be separated into three groups. The first group,
comprising of three isolates (52b, 73, 93), gave similar restriction patterns
suggesting that they are the same species. Isolate 58b yielded a distinct
profile while isolate 97 had similar sized ITS-PCR (1000bp) to that of L. lipofer
and L. tetrasporus . It is important to assess the variation in RFLP profiles
between various strains from different habitats of a particular species in order
to determine the conserved status of this genotypic character. More strains of
a species representing the Lipomycetaceae should be subjected to similar
RFLP analysis to further determine its conserved status.
The D1/D2 sequence data enabled separation of the five isolates into three
groups. The first group, comprising of three isolates, showed 1% nucleotide
substitutions to L. starkeyi suggesting that these isolates are probably known
Lipomyces spp. The other two isolates yielded sequences that were 99%
identical to L. kononenkoae subsp. kononenkoae (isolate 58b) and 100%
identical to that of L. tetrasporus (isolate 97) further suggesting that these
isolates are probably known Lipomyces species.
Isolation of basidiomycetous yeasts from unusual carbon sources has been
reported, however, this is the first report of isolation of ascomycetous yeasts
able to grow on unusual substrates. The substrate that yielded the highest
number of isolates was 1,4 cyclohexanedimethanol. Pichia anomala and Y. lipolytica strains (identity confirmed with D1/D2
sequencing) isolated from 2-chlorobutyric acid could not degrade the 2-chlorobutyric
acid probably due to toxicity of low molecular weight organic
acids at low pH. The ability of P. anomala isolated from 1,4
cyclohexanedimethanol to grow on dodecane and pristane is unusual and this
strain should also be subjected to sequencing to confirm identification.
Debaryomyces hansenii, P. anomala, P. fabianii, P. guilliermondii and Y.
lipolytica could grow on the cyclohexane derivatives although they preferred a
shorter straight chain hydrocarbon as confirmed by higher growth rates in the
presence of dodecane.
The isolates could not grow in the presence of monoterpenes, although they
had been isolated from substrates that were supposed to mimic the structures
of monoterpenes and which previously had yielded limonene utilizing
Rhodotorula species. The inability of these strains to grow on monoterpenes
might be due to toxicity of the monoterpenes, because of their hydrophobicity
and lipophilicity resulting in partitioning into the lipid bilayer of cell
membranes.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-09292005-160929 |
| Date | 29 September 2005 |
| Creators | Tarr, Shahida |
| Contributors | Dr J Albertyn, Prof JLF Kock, Prof MS Smit |
| 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-09292005-160929/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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