Thesis (MSc)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: It is commonly known that a diversity of fungi, including yeasts, may occur on
plant surfaces. Similarly, on fallen trees an ecological succession of different
fungal species is known to occur during wood degradation. Some of these fungi
may be pioneer fungi contributing to the initial degradation process, while others
may be yeasts associated with the fruiting bodies of macro-fungi which in turn
are able to utilize the more recalcitrant polymers in wood. Previously, it was
revealed that an increase occurs in the wood degradation rate of certain white-rot
fungi when co-cultured with selected yeast species.
A well known inhabitant of decomposing trees is the white rot fungus Pycnoporus
sanguineus. It was found by some that this fungus is capable of selective
delignification while growing on the wood of poplar trees, while other authors
found a simultaneous delignification pattern on Eucalyptus grandis trees. In the
latter case cellulose and lignin are degraded simultaneously.
We were interested in how yeasts occurring on the surface of P. sanguineus
fruiting bodies, and the pioneer fungus Aspergillus flavipes, impact on wood
degradation by this white-rot fungus. Restriction Fragment Length
Polymorphisms (RFLP) analyses were used to obtain an indication of the species
composition of the culturable yeast community associated with fruiting bodies of
P. sanguineus. The impact of the most dominant of these yeasts species, i.e.
Pichia guilliermondii and Rhodotorula glutinis, as well as A. flavipes, on wood
degradation by P. sanguineus was then determined by analyzing the major wood
components after growth of co-cultures on hot water washed E. grandis wood
chips. Co-cultures of P. sanguineus with the other fungi were prepared by
inoculating the wood chips, contained in solid state bioreactors and
supplemented with molasses and urea, with the an appropriate volume of fungal
inoculum, resulting in an initial moisture content of 60%. After two weeks of
incubation at 30°C with constant aeration, the chips were harvested. Standard protocol (TAPPI Standard Methods), commonly used by the paper and pulp
industry, were then employed to determine the percentage cellulose, Klason
Lignin, as well as polar and solvent-borne extractives in the chips. The resulting
data were analyzed using box plots, as well as biplots. No degradation of Klason
lignin was observed, while the percentage cellulose did decrease during fungal
degradation. Taking into account the inherent shortcomings of the Klason Lignin
determination, the results supported the findings of others that P. sanguineus
shows a simultaneous delignification pattern while growing on E. grandis wood.
In addition, it was found that the yeasts played no significant role in the
degradation ability of P. sanguineus, while A. flavipes showed an antagonistic
effect on P. sanguineus with respect to cellulose degradation. However, it was
clear that the analytical methods used in this study were inadequate to accurately
determine fungal degradation of wood. In addition, it was obvious that the
methods used did not distinguish between fungal biomass and wood
components. Nevertheless, the methods provided us with a fingerprint of each
culture growing on E. grandis wood, allowing us to compare the chemical
composition of the different cultures and the un-inoculated hot water washed
wood chips. The question, therefore, arose whether the effect of a particular coculture,
on the chemical composition of wood, differs between tree species.
Consequently, chemical alterations in different tree species, induced by a P.
sanguineus / A. flavipes co-culture, were investigated in the next part of the
study. Wood chips originating from four tree species, i.e. Acacia mearnsii,
Eucalyptus dunnii, E. grandis, and Eucalyptus macarthurii, were inoculated with
this co-culture. The culture conditions and subsequent analyses of the wood
components were the same as in the first part of the study. From the box- and
biplots constructed from the resulting data, it was clear that the chemical
composition of each tree species were altered in a different manner by the coculture.
Lignin content showed an apparent increase in A. mearnsii, while E.
dunnii showed a decrease in cellulose content. The results indicate that wood of
different tree species are degraded in a different manner and this phenomenon
should be taken into account in selecting fungi for biopulping. / AFRIKAANSE OPSOMMING: Dit is algemeen bekend dat 'n verskeidenheid fungi, insluitend giste, op
plantoppervlaktes mag voorkom. Dit is ook bekend dat 'n ekologiese
opeenvolging van verskillende fungusspesies tydens hout-afbraak op omgevalle
bome voorkom. Van hierdie fungi mag pionierfungi wees wat bydra tot die
aanvanklike afbraakproses, terwyl ander giste mag wees wat geassosieer word
met die vrugliggame van makro-fungi, wat op hul beurt weer in staat is om die
meer weerstandbiedende polimere in hout te benut. Dit is voorheen
bekendgemaak dat daar 'n toename plaasvind in die tempo van houtafbraak deur
sekere witvrot-fungi wanneer dit in ko-kulture met geselekteerde gisspesies
voorkom.
'n Bekende bewoner van verrottende bome is die wit-vrotfungus Pycnoporus
sanguineus. Dit is gevind dat hierdie fungus tot selektiewe delignifikasie in staat
is terwyl dit op die hout van populierbome groei, terwyl ander outeurs 'n
gelyktydige patroon van delignifisering op Eucalyptus grandis bome gevind het.
In laasgenoemde geval is sellulose en lignien gelyktydig afgebreek.
Ons was geïnteresseerd in die effek van giste op die oppervlak van vrugliggame
van P. sanguineus, en die pionierfungus Aspergillus flavipes, op die houtafbraak
deur hierdie wit-vrotfungus. Restriction Fragment Length Polymorphisms (RFLP)
analises is gevolglik gebruik om 'n aanduiding te kry van die spesiesamestelling
van die kweekbare gisgemeenskap wat met die vrugliggame van P. sanguineus
geassosieer word. Die impak van die mees dominante van hierdie gisspesies,
naamlik Pichia guilliermondii en Rhodotorula glutinis, asook A. flavipes, op
houtafbraak deur P. sanguineus is voorts bepaal deur die analise van die
belangrikste houtkomponente na die kweek van ko-kulture op E. grandis
houtskyfies wat met warm water gewas is. Ko-kulture van P. sanguineus met die
ander fungi is voorberei deur die houtskyfies in vaste fase bioreaktore, aangevul
met melasse en ureum, te inokuleer met 'n toepaslike volume van die fungus inokulum om 'n aanvanklike voginhoud van 60% te verkry. Na twee weke se
inkubasie by 30°C met konstante belugting is die skyfies ge-oes. Standaard
protokol (TAPPI Standard Methods), algemeen deur die papier en pulpindustrie
gebruik, is ingespan om die persentasie sellulose, Klason Lignien, asook polêre
en oplosmiddel-gedraagde ekstrakte in die skyfies te bepaal. Die gevolglike data
is geanaliseer deur gebruik te maak van box plots en biplots. Daar is geen
afbraak van Klason Lignien bespeur nie, terwyl die persentasie sellulose wel
toegeneem het tydens fungus degradasie. Met die inherente tekortkominge van
die Klason Lignien bepaling inaggenome, het die resultate die bevindings
ondersteun van andere wat getoon het dat P. sanguineus 'n gelyktydige
delignifikasiepatroon openbaar terwyl dit op E. grandis hout groei. Daarby is dit
gevind dat die giste geen beduidende rol in die afbraakvermoeë van P.
sanguineus gespeel het nie, terwyl A. flavipes 'n antagonisiese effek ten opsigte
van die sellulose degradering van P. sanguineus getoon het. Dit was egter
duidelik dat die analitiese metodes wat in hierdie studie gebruik is, onvoldoende
was om die degradering van hout akkuraat te bepaal. Daarby was dit duidelik
dat die metodes nie tussen fungus biomassa en houtkomponente kon onderskei
nie. Nogtans het die metodes 'n vingerafdruk verskaf van elke kultuur wat op E.
grandis hout groei, wat ons toegelaat het om die chemiese samestelling van die
verskillende kulture en die ongeïnokuleerde, met warm water gewasde
houtskyfies te vergelyk. Die vraag het gevolglik ontstaan of die effek van 'n
bepaalde ko-kultuur op die chemiese samestelling van hout van boomspesie tot
boomspesie verskil. Gevolglik is die chemiese wisselinge in verskillende
boomspesies, geïnduseer deur 'n P. sanguineus / A. flavipes ko-kultuur, in die
volgende gedeelte van die studie ondersoek. Houtskyfies van vier boomspesies,
naamlik Acacia mearnsii, Eucalyptus dunnii, E. grandis, en Eucalyptus
macarthurii, is met hierdie ko-kultuur geïnokuleer. Die kultuurkondisies en
daaropvolgende analises van die houtkomponente was dieselfde as in die eerste
deel van die studie. Van die box- en biplots wat van die resultate getrek is, is dit
duidelik dat die chemiese samestelling van elke boomspesie op 'n verskillende
manier deur die ko-kulture verander is. Lignien-inhoud het ’n waarskynlike toename getoon in A. mearnsii, terwyl E. dunnii 'n afname in sellulose-inhoud
getoon het. Die resultate toon dat hout van verskillende boomspesies op
verskillende maniere afgebreek word en dat hierdie fenomeen in aanmerking
geneem moet word wanneer fungi vir bioverpulping geselekteer word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/19884 |
| Date | 03 1900 |
| Creators | Van Heerden, Andrea |
| Contributors | Botha, A., 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 | xii, 94 leaves : ill. |
| Rights | Stellenbosch University |
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