- Title
- Streptomyces as a source of Geosmin and 2-methylisoborneol associated taste and odour episodes in drinking water reservoirs
- Creator
- Asquith, Elise Anne
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2015
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Providing adequate volumes of safe, clean drinking water to the world’s growing population is a continuous and increasing challenge for water utilities. While prime attention is placed on health aspects, consumers generally judge water quality by its aesthetic value. The presence of compounds which impart taste and odour (T&O) in drinking water supplies often leads to the misconception that the water is unsafe for consumption, triggering consumer complaints and high treatment costs for water utilities. Two biologically sourced compounds which respectively cause ‘earthy’ and ‘musty’ T&O in drinking water supplies worldwide are the secondary metabolites geosmin and 2-methylisoborneol (2-MIB). The research presented in this thesis was initiated and supported by Hunter Water Corporation (NSW, Australia) in response to earthy-musty T&O problems periodically experienced in drinking water supplies (Grahamstown and Chichester Reservoirs). A preliminary analysis of historical water quality data in these reservoirs revealed a close association between abundance of the cyanobacterial genus Anabaena and elevated concentrations of geosmin, while 2-MIB could not be reliably linked to any routinely measured parameter. Although T&O events are notoriously ascribed to cyanobacteria, the filamentous bacterial genus Streptomyces, major producers of geosmin and 2-MIB in soil, have long been suspected to also play a potential role in imparting these metabolites into drinking water supplies. There has been a distinct paucity of knowledge regarding their ecology in freshwater environments and consequently, their significance as contributors to T&O events is not well-established. This thesis presents both field- and laboratory-based studies which were conducted in order to examine the potentiality of Streptomyces to contribute to earthy-musty T&O problems in drinking water reservoirs. A temporal and spatial sampling program combined with the application of a molecular technique for Streptomyces quantification (qPCR targeting the 16S rRNA gene) established the widespread distribution and abundance of these bacteria within the water mass, bottom sediments and in marginal substrates of the reservoirs. The detection of significantly greater Streptomyces population densities in the water mass during prolonged wet conditions compared to extended dry conditions provided evidence to support the hypothesis that they are washed from surrounding marginal habitats into the reservoirs, consistent with them being ‘terrestrial’ bacteria. Contradicting widespread opinion in the literature that they are not ‘aquatic’ bacteria and survive only as dormant spores in water, vegetative cells (detected through a differential cell lysis protocol for DNA extraction) were found to comprise a considerable proportion of Streptomyces populations in the water mass. Together with the finding that sterilised reservoir water supported the growth and geosmin and 2-MIB production by Streptomyces spp. in the laboratory indicates the potentiality of these bacteria to be metabolically active in water and contribute to in situ production of T&O metabolites.Substrates at the margins of the reservoirs including soil, sediment and plant debris represented the major habitat of Streptomyces and the hypothesis that exposure of such substrates following water level recession during dry conditions stimulates the growth and activity of these aerobic bacteria, was largely supported by both field data and a laboratory simulation of these conditions. Together these studies indicated the potential significance of marginal substrates as a major source of Streptomyces and their T&O metabolites, which can enter the adjacent water mass following rain events. Confirmation that all Streptomyces reservoir cultivars could produce geosmin and 2-MIB provided additional evidence to support their role as potentially significant contributors to T&O metabolites in drinking water supplies. Multivariate laboratory studies examining the influence of physico-chemical factors on the production of geosmin and 2-MIB by Streptomyces spp. established that the production of these T&O metabolites was highly coordinated with the reproductive (sporulation) stage of the Streptomyces life cycle. Thus physico-chemical factors that trigger Streptomyces to cease vegetative growth and enter the reproductive developmental stage would conceivably allow elucidation of the conditions which also trigger significant production of their T&O metabolites. Such conditions included lowest concentrations of macronutrients (C, N and P) while higher concentrations of NaCl and copper were found to favour vegetative growth and thus inhibit T&O metabolite production. In consideration of these results, the levels of physico-chemical characteristics in the surface waters of Grahamstown and Chichester Reservoirs appear to be suitable for Streptomyces growth, differentiation and production of geosmin and 2-MIB. While the biological function of geosmin and 2-MIB is not currently known, many other secondary metabolites produced by Streptomyces function as antimicrobial compounds, produced during times of adversity to antagonise competing microorganisms and coincide with their initiation of reproductive growth. Having established that geosmin and 2-MIB production was stimulated under conditions which also trigger reproductive growth (e.g. nutrient limitation), it was hypothesised that they too may function as antimicrobial compounds, however subsequent co-culturing and antimicrobial assays led to the rejection of this hypothesis. Based on literature evidence, several alternative propositions are outlined regarding the possible biological function of these compounds related to regulation of the formation, germination and dispersal of Streptomyces spores. The findings of the studies presented in this thesis indicate the potential significance of Streptomyces as major contributors to the occurrence of geosmin and 2-MIB in drinking water supplies. Furthermore, understanding of the influence of environmental factors and Streptomyces life cycle stage on the biosynthesis of these compounds and their possible biological function has been extended.
- Subject
- drinking water; taste; odour; water utilities; cyanobacterial genus Anabaena; geosmin; Streptomyces; bacteria
- Identifier
- http://hdl.handle.net/1959.13/1305783
- Identifier
- uon:21097
- Rights
- Copyright 2015 Elise Anne Asquith
- Language
- eng
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