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Isolation and Characterisation of Bacterial Metabolites as Potential Wood Preservatives

The durability of wood has traditionally relied on the use of heavy metals and toxic compounds to deter wood degrading fungi. Conventional wood preservatives such as Chromated Copper Arsenate (CCA) have been widely used to control wood degrade for many decades, however public pressure over perceived environmental and health risks have led to recent restrictions for use in some countries. This issue has focused the need for research towards environmentally friendly (benign) wood preservatives including compounds such as plant extractives and microbial metabolites. Previously chilli waste has been shown to have moderate antifungal activity against common wood sapstain fungi. Furthermore, Lactobacillus sp. isolated from chilli showed synergistic activity with chilli against these fungi. The intention of this study was to further develop this work, by isolating and identifying the range of bacteria from chilli waste, screening for antifungal activity against wood decay fungi then investigating any possible synergy between the isolates and chilli waste. Initially a quick screening 96-well optical density assay was optimised which allowed the screening of lactic acid bacterial metabolites against wood decay fungi. This technique proved to be comparable to a commonly used growth rate method and has potential as a standard initial screening method in the laboratory. Seven isolates from chilli juice had an antifungal effect on the wood decay fungus Oligoporus placenta and were identified using 16S rRNA phylogenetic techniques as Lactobacillus brevis, Leuconostoc mesenteroides subsp. mesenteroides (three isolates), L. mesenteroides subsp. cremoris, L. pseudomesenteroides and Gluconobacter oxydans. Cell-free supernatants of these isolates were used to treat wood blocks which were then exposed to wood decay fungi. L. brevis metabolites showed the greatest inhibition of wood decay and were identified as lactic and acetic acids by high performance liquid chromatography (HPLC) amongst other techniques. The media in which the bacteria were grown also had an antifungal effect on wood decay fungi most likely due to its hygroscopicity increasing wood moisture content to a point inhibitory to decay fungi. Synergy between the bacterial metabolites and chilli juice was examined using the optical density assay and it was discovered that two bacteria showed complete inhibition of decay fungi when grown in chilli juice. However, when subjected to a wood assay, both L. brevis and L. mesenteroides subsp. cremoris did not give satisfactory control of decay fungi suggesting the main mechanism of fungal inhibition was due to increased moisture content of wood induced by the specific media initially used in this study. Further research should determine whether the isolated bacteria can be induced to increase metabolite production and if this would improve antifungal activity. Ultimately these bacterial metabolites and chilli combined or alone, may not be suitable for long term protection against wood decay, but may provide a solution to other fungal degradation issues.
Type of thesis
O’Callahan, D. R. (2012). Isolation and Characterisation of Bacterial Metabolites as Potential Wood Preservatives (Thesis, Master of Science (MSc)). University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/6509
University of Waikato
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