Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The global rise in microbial resistance, ranging from the agricultural industry to the medical
sector, has created the urgent need for novel or supplementary antibiotics. Antimicrobial
peptides or “nature’s antibiotics” may be the answer to this major problem. In this study a group
of antimicrobial peptides, cyclic decapeptides named tyrocidines, produced by the soil bacterium
Bacillus aneurinolyticus, was investigated for their antifungal activity, possible mode of
antifungal action and potential applications.
The study illustrated that the tyrocidines have significant antifungal activity against a range of
phytopathogens, including Fusarium solani and Botrytis cinerea, as well as the human pathogen
Candida albicans. The activity of the tyrocidines is influenced by the identity of both the target
organism and the media environment. Further evidence was obtained in support of the
hypothesis that the tyrocidines are extremely sensitive to their environmental conditions and that
they tend to self-assemble to form oligomers. The assessment of a small tyrocidine library and
analogues, comprised of eight peptides, revealed no overt structure-activity relationships against
fungal pathogens, except for the importance of a tyrosine residue. This indicated an important
role for the conserved sequence of the tyrocidines, NQYVOLfP, together with the tendency of
the tyrocidines to oligomerise into higher-order active structures in their antifungal activity.
The tyrocidines were found to be membrane active toward the fungal pathogens. However,
supporting evidence was also obtained for additional mode(s) of antifungal action for the
tyrocidines which inter alia induces morphological abnormalities in filamentous fungal target
cells. Furthermore, the results also indicated that the membrane activity of the tyrocidines may
be influenced by additional factors to that of the composition of the target cell membrane, for
instance components of the fungal cell wall. This investigation also indicated the significant potential of the tyrocidines to be developed for
the commercial sector. The potent activity of the tyrocidines against agronomically important
phytopathogens (significantly higher than the commercial fungicide bifonazole) together with
their relative salt stability bodes well for their development as bio-fungicides for the agricultural
sector. The tyrocidines also exhibited an overt sinergistic effect on the in vitro candidacidal
activity of two key antifungal drugs, caspofungin and amphotericin B. Furthermore, tyrocidine A
and caspofungin exhibited synergistic activity in vivo which had a significant positive effect on
the survival of C. albicans infected Caenorhabditis elegans. Latter results highlighted their
potential to serve as candidates for combinatorial treatment in the medical industry. / AFRIKAANSE OPSOMMING: Die globale verskynsel van mikrobiese weerstand, wat strek vanaf die landbou sektor tot in die
mediese bedryf, het ’n dringende behoefte vir die ontwikkeling van nuwe antmikrobiese middels
geskep. Antimikrobiese peptiede of “die natuur se antibiotika”, kan moontlik die antwoord op
hierdie ernstige problem wees. Tydens hierdie studie is ‘n groep sikliese antimikrobiese
peptiede, naamlik die tirosidiene wat deur die grondbakterium Bacillus aneurinolyticus
geproduseer word, vir hulle antifungiese aktiwiteit, hulle moontlike meganisme(s) van
antifungiese werking en hulle potensiёle aanwendings bestudeer.
Hierdie studie het getoon dat die tirosidiene uitsonderlike antifungiese aktiwiteit teen ‘n reeks
fitopatogene, insluitend Fusarium solani en Botrytis cinerea, asook teen die mens patogeen
Candida albicans het. Die aktiwiteit van die tirosidiene is deur beide die identiteit van die
teikenorganisme sowel as die mediumomgewing beїnvloed. Daar is ook verdere bewyse verkry
wat die hipotese dat tirosidiene uiters sensitief is tot hulle omgewing en dat hulle neig om te
oligomeriseer, ondersteun. Die studie van die klein tirosidien-biblioteek, saamgestel uit agt
tirosidiene en analoё, het geen ooglopende struktuur-aktiwiteit verwantskappe opgelewer nie,
behalwe vir die oёnskynlike invloed van die tirosien-residu. Laasgenoemde het die belangrikheid
van die gekonserveerde aminosuurvolgorde van die tirosidiene, NQYVOLfP, asook die neiging
van tirosidiene om hoё-orde aktiewe strukture te vorm deur self-verpakking, beklemtoon.
Tydens die studie is daar gevind dat die tirosidiene membraan-aktiewiteit toon teenoor fungiese
patogene. Daar is egter ook goeie bewyse vir alternatiewe meganisme(s) van antifungiese
werking, wat ondermeer tot morfologiese abnormaliteite in filamentagtige fungi-teikenselle lei,
vir die tirosidiene verkry. Die resultate het verder ook daarop gewys dat die membraan-aktiwiteit van die tirosidiene ook deur ander faktore, soos deur komponente van die fungiese selwand, en
nie net deur die samestelling van die fungiese membraan beїnvloed word nie.
Hierdie ondersoek het ook die aansienlike potensiaal van die tirosidiene vir kommersiёle
ontwikkeling en gebruik uitgelig. Die merkwaardige aktiwiteit van die tirosidiene teen
fitopatogene van agronomiese belang (wat selfs beter as diè van die kommersiёle swamdoder
bifonazole was) tesame met die relatiewe sout stabiliteit van die tirosidiene, is belowende tekens
om die tirosidiene as bio-swamdoders vir die landbou sektor te ontwikkel. Die tirosidiene het
ook ‘n uitgesproke sinergistiese effek op die in vitro candidasidiese aktiwiteit van twee sleutel
antifungiese middels, caspofungin en amphotericin B, getoon. Verder is daar in vivo sinergistiese
aktiwiteit gewys deur die kombinasie van tirosidien A en caspofungin wat ’n beduidende
positiewe effek op die oorlewing van C. albicans geïnfekteerde Caenorhabditis elegans gehad
het. Laasgenoemde dui op die potensiaal van die tirosidiene om in die mediese bedryf as
kandidate vir kombinasie-behandeling te dien.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/86162 |
| Date | 04 1900 |
| Creators | Troskie, Anscha Mari |
| Contributors | Rautenbach, Marina, Stellenbosch University. Faculty of Science. Dept. of Biochemistry. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 215 p. : ill. |
| Rights | Stellenbosch University |
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