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Title: Studies in mycelial interactions between two species of tropical higher fungi
Author: Gregorio, Ana Paula Ferreira
ISNI:       0000 0004 2671 5557
Awarding Body: University of Westminster
Current Institution: University of Westminster
Date of Award: 2007
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During the studies of interactions on agar media between mycelia of the two tropical agaric fungi, Marasmius pallescens and Marasmiellus troyanus, it was observed that initial deadlock between the mycelial fronts was ultimately followed by overgrowth by M troyanus. This was shown to be the most consistent outcome even when abiotic conditions (pH, aw, temperature) were altered to possibly favor the competitive ability of M pallescens on agar. However, a shift in competitive ability was observed when Birch wood disks precolonized with mycelia of both taxa were confronted in the inoculum ratio of 75:25 M pallescens to M troyanus. In this instance, M pallescens was not only able to retain its resource, but also capture a small portion of resource originally colonized by M troyanus. In studies on the expression of lignocellulose degrading enzymes in liquid cultures ofthese two fungi it was found that when the two taxa were mixed, a rapid increase in laccase and manganese peroxidase activity, but not lignin peroxidase, was detected in the culture supernatant. Even more rapid and elevated induction of laccase was observed when filtersterilized supernatant of M pallescens was added to M troyanus cultures, but the reciprocal experiment (addition ofM troyanus supernatant to M pallescens cultures), did not lead to any increase in laccase activity. Addition of autoclaved supernatant ofM pallescens also induced laccase activity from M troyanus cultures, but over a period of days rather than hours. Although bothM troyamls, and to a lesser extentM pallescens, are able to produce laccases in shaken liquid culture following addition of the inducer 2,5Dimethylalanine, these experiments suggested that the presence of heat-stable and heatlabile laccase inducers, secreted byM pallescens mycelia, led to induction of laccases by M troyanus. ReacSyn™ bioreactors were then successfully used to assay for the induction of laccase and the production of phenolic metabolites in mixed cultures ofM troyamls and M pallescens, utilizing a working volume of 30 ml. The induction of laccase in combined cultures was demonstrated in both shaken ReacSynTM and static ReacSynTM systems, although to a greater extent in the shaken system. A greater change in the quantity and type ofphenolics was detected in combined culture extracts, than in either monoculture control extract. HPLC analysis of extracts produced from culture filtrates from combined cultures and monocultures controls revealed that the phenolic compound that was eluted at eight minutes was produced in highest quantity by M pallescens and appeared to have induced laccase production in M troyanus in combined cultures, and as a result of laccase action could have been partially polymerized. Compounds unique to combined culture profiles were also shown to be present in both the liquid media and the gaseous headspace, when combative interactions between mycelia of both taxa was scaled up to 2 I STR. GC-MS analysis identified a-hydroxyphenylacetic in the culture filtrates of interacting liquid cultures. This compound is a natural mediator of phenolic degradation, and could thus play a role in laccase induction during combative interactions. Moreover, the presence ofan array of volatile compounds unique to combined cultures, suggests that chemicals are involved in offensive/defensive strategies used byM troyamls andM pallescens during mycelial interactions at a distance.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available