Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The ascomycetous yeast, Candida albicans, has been almost exclusively studied in a clinical context,
due to the medical risk and costs associated with the yeast. Most environmental research into the
external survival of this opportunistic pathogen has been concerned with short-term, severe pollution
challenges. However, a study of literature indicates that the habitat characteristics of the oxygenlimited
zones in wetlands and riverbanks are comparable to those of the gastrointestinal source of
sewage-borne C. albicans. Interestingly, these are the external, environmental regions to which
sewage-borne C. albicans is often exposed. In addition, oxygen-limitation is the predominant
parameter in stimulating conjugation of C. albicans. Based on these observations, this study aimed to
assess polluted river bank and wetland environments in the Western Cape of South Africa as potential
habitats to accommodate a niche for C. albicans, particularly comparing the presence of this yeast in
oxygen-limited, plant debris-rich zones and aerobic, clear, flowing zones. The second objective was to
employ in vitro microcosm studies to investigate the survival and growth of C. albicans in various
microhabitats similar to those comprising the oxygen-limited zones of wetlands. These included the
rhizosphere of wetland flora, various soil and mud types and decomposing plant debris. The final
objective was to establish the presence of sufficient nutrient and energy sources within this
environment for the growth of C. albicans. In particular, cellulosic substrates and mono- and
disaccharides released by the natural degradation of wetland plant debris were investigated as potential
energy sources for this human commensal in the wetland environment. These study objectives
combined to demonstrate the potential of such an oxygen-limited, plant debris-rich environment as a
niche for C. albicans external to its human host.
Both semi-quantitative culturing techniques and quantitative Real-Time PCR demonstrated the
improved survival of C. albicans in oxygen-limited, plant debris-rich zones in wetland and river bank
environments, in comparison to aerobic, clear subsurface water zones in the same environments. These
zones were compared in the Plankenburg and Diep Rivers, situated in the Western Cape of South
Africa. Correlations between coliform concentrations and total yeast concentrations were demonstrated
in each of the different river zones, with higher pollution levels characteristic of the dry season.
Candida albicans numbers in flowing water (zone W), rock-filtered (zone R) and plant-filtered water
(zone P) were compared during the progress of the rainy and dry seasons. No C. albicans was observed
in clear, flowing water throughout the analysis. Early in the rainy season, both rock-filtered (aerobic,
poor in plant debris) and plant-filtered (oxygen-limited, rich in plant debris) water demonstrated C. albicans numbers at approximately equivalent levels of 10²-10³ cells/100 mL. However, as the rainy
season progressed and total yeast and coliform numbers in all zones of the rivers dropped to negligible
levels, C. albicans could no longer be detected in aerobic, rock-filtered zones; but its numbers
remained at constant levels in oxygen-limited, plant-filtered zones. This suggests that oxygen-limited
wetland and river bank zones rich in plant matter, analogous to the human gastrointestinal tract, may
provide an ideal habitat in which C. albicans could establish a niche external to its host.
The survival of this yeast in the various microhabitats that comprise this anaerobic, reducing wetland
environment was evaluated with in vitro microcosms. The rhizosphere of wetland plants had no
influence on C. albicans growth and survival in comparison to bulk soil away from the plant, and
wetland mud microbiota was demonstrated to be inhibitory to its survival. However, decaying plant
debris was shown to increase the survival of the yeast in this inhibitory mud environment. Candida
albicans was shown to compete well saprophytically in anaerobic plant debris microcosms. In addition,
the tendency of C. albicans to associate with plant matter in an aquatic environment was demonstrated
by inoculating the yeast in water containing Hydrilla, a submerged macrophyte found in South African
aquatic environments. Plate and liquid analyses, as well as an ANKOM NDF analysis, indicated
unequivocally that the C. albicans strains evaluated in this work were unable to utilise the complex
carbohydrates of the wetland habitat, including cellulose and fibre. However, HPLC, along with GCMS,
demonstrated the anaerobic assimilation by C. albicans of monosaccharides released by natural
lignocellulose degradation of wetland plant matter. An analysis of total nitrogen by digestion in a
nitrogen analyser, as well as evaluation of ammonium, nitrate and nitrite in a KCL extract, also showed
that C. albicans assimilates nitrogenous compounds released by the decomposition of wetland plant
matter. This decay process occurs constantly in wetland and river bank habitats. It may therefore
provide energy and nutrients for C. albicans, particularly in the anaerobic zones where conjugation
may possibly occur and a niche may be established, as indicated by the results obtained for the
Plankenburg and Diep Rivers. / AFRIKAANSE OPSOMMING: Die askomisete gis Candida albicans is feitlik eksklusief in ‘n kliniese konteks bestudeer weens die
mediese risiko en koste daaraan verbonde. Die meeste omgewingsnavorsing op die eksterne oorlewing
van hierdie opportunistiese patogeen was toegespits op die uitdagings van ernstige korttermyn
besoedeling. ‘n Literatuurstudie toon egter dat die habitat-eienskappe van die suurstof-beperkte sones
in vleilande en rivieroewers vergelykbaar is met dié van die gastroïntestinale bron van C. albicans wat
in riool gevind word. Interessant genoeg is dit juis hierdie eksterne omgewingsgebiede waaraan C.
albicans vanuit riool dikwels blootgestel word. Hierby is suurstof-beperking die vernaamste parameter
in die stimulering van konjugasie in C. albicans. Op grond van hierdie waarnemings poog dié studie
om besoedelde vleilande en rivieroewers in die Wes-Kaap Provinsie van Suid-Afrika te evalueer as
potensiële habitatte wat ‘n nis van C. albicans kan akkommodeer, en veral om die teenwoordigheid van
hierdie gis in suurstof-beperkte sones ryk aan plantafval te vergelyk met aerobe, helder, vloeiende
sones. Die tweede doelwit was om in vitro mikrokosmos studies te gebruik om die oorlewing en groei
van C. albicans in verskillende mikrohabitatte soortgelyk aan suurstof-beperkte sones in vleilande te
ondersoek. Dit sluit die risosfeer van vleilandflora in, asook verskillende grond- en moddertipes en
ontbindende plantafval. Die laaste doelwit was om die teenwoordigheid van genoegsame voedings- en
energiebronne in dié omgewing te bepaal vir die groei van C. albicans. In besonder is sellulose
substrate, asook die mono- en di-sakkariede, wat deur die natuurlike afbraak van vleiland plantafval
vrygestel word, as potensiële energiebronne van hierdie mens-kommensaal in die vleiland-omgewing
ondersoek. Hierdie studiedoelwitte het gesamentlik die potensiaal van so ‘n suurstofbeperkte,
plantafvalryke omgewing as ‘n nis vir C. albicans buite die menslike gasheer aangetoon.
Beide semi-kwantitatiewe kweektegnieke en kwantitatiewe in-tyd PKR het die verbeterde oorlewing
van C. albicans in suurstofbeperkte, plantafvalryke sones in vleiland en rivieroeweromgewings
gedemonstreer, in teenstelling met aerobe, helder oppervlakwatersones in dieselfde omgewings.
Hierdie sones in die Plankenburg- and Dieprivier in die Wes-Kaap Provinsie, Suid-Afrika, is met
mekaar vergelyk. Korrelasies tussen coliform konsentrasies en totale giskonsentrasies is in elk van die
verskillende sones in dié riviere gedemonstreer, met hoër vlakke van besoedeling kenmerkend aan die
droër seisoen. Candida albicans getalle in vloeiende water (sone W), rots-gefiltreerde (sone R) en
plant-gefiltreerde water (sone P) is deur die verloop van die reën- en droë seisoene met mekaar
vergelyk. Geen C. albicans is deur die loop van die analises in helder, vloeiende water bespeur nie.
Vroeg in die reënseisoen het beide rots-gefiltreerde (aerobe, min plantafval) en plant-gefiltreerde (suurstofbeperk, ryk in plantafval) water vergelykbare vlakke van C. albicans getoon, naamlik 10²-10³
selle/100 mL. Soos die reënseisoen egter verloop het en die totale gis- en coliforme getalle in al die
sones van die riviere tot weglaatbare vlakke gedaal het, kon C. albicans egter nie meer in die aerobe,
rots-gefiltreerde sones bespeur word nie, hoewel die getalle in suurstofbeperkte, plant-gefiltreerde
sones konstant gebly het. Dit dui daarop dat suurstof-beperkte vleiland en rivieroewer sones ryk in
plantmateriaal, analoog tot die menslike gastroïntestinale kanaal, die idealke habitat mag bied waarin
C. albicans ‘n nis mag vind buite sy gasheer.
Die oorlewing van hierdie gis in die verskillende mikrohabitatte wat uit hierdie anaerobe, reduserende
vleilandomgewing bestaan, is met in vitro mikrokosmosse geëvalueer. Die risosfeer van vleilandplante
het in vergelyking met die grond weg van die plant geen effek op die groei en oorlewing van C.
albicans gehad nie, en vleiland modder-mikrobiota is gevind om die oorlewing daarvan te inhibeer.
Verrottende plantafval het egter die oorlewingsvlakke van giste in hierdie inhiberende
modderomgewing verbeter. Candida albicans kan egter saprofities goed kompeteer in anaerobe
plantafval mikrokosmosse. Hierby is die geneigdheid van C. albicans om met plantmateriaal in
waterige omgewings te assosieer gedemonstreer deur die gis te innokuleer in water wat Hydrilla, ‘n
onderwater makrofiet wat in Suid-Afrikaanse akwatiese omgewings aangetref word, bevat. Plaat en
vloeibare analises, asook ‘n ANKOM NDF data-analise, het onteenseglik getoon dat die C. albicans
stamme wat in dié werk gebruik is, nie in staat was om die komplekse koolhidrate, insluitende sellulose
en vesel, van die vleiland habitat te benut nie. HPLC, saam met GC-MS, toon egter C. albicans se
anaerobe assimilasie van monosakkariede wat deur natuurlike lignosellulose afbraak van vleiland
plantmateriaal vrygestel is. ’n Totale stikstof analise deur vertering in ’n stikstof analiseerder, en ’n
evalueering van ammonium, nitraat en nitriet in ‘n KCl ekstrak, het ook getoon dat C. albicans
stikstofverbindings assimileer wat deur die afbraak van vleiland plantmatriaal vrygestel word. Hierdie
afbraakproses kom deurlopend in vleiland en rivieroewer habitatte voor en verskaf potensieel energie
en voedingstowwe aan C. albicans, spesifiek in die anaerobe sones waar konjugasie moontlik kan
plaasvind, en ‘n nis gevestig kan word, soos aangedui deur die Plankenburg- and Dieprivier.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6892 |
| Date | 03 1900 |
| Creators | Stone, Wendy |
| Contributors | Botha, Alf, Wilsenach, Jac, Stellenbosch University. Faculty of Science. Dept. of Microbiology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 117 pages : illustrations |
| Rights | Stellenbosch University |
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