The diversity and function of peatland actinobacteria

The issue of ecosystem carbon (C) cycling is high on the scientific and political agenda, largely because of concerns over the ability of terrestrial ecosystems to act as C stores in the face of climate and other global change (Beedlow et al. 2004; Freeman et al. 2004; Schlesinger 2006). Much of the interest in this area is focused on peatlands because they represent a vast store of terrestrial C, currently estimated to be one-third of the global C stock (Gorham 1991). The main concern is that changes in climate and land use will destabilise these stores, releasing C in gaseous (CO2 and CH4) and aqueous (DOC) forms into the surrounding environment (Freeman et al. 2004) with feedback implications for climate change and water quality (Mitchell 1989; Beedlow et al. 2004). To date, most research in this area has focused on abiotic drivers of peatland C cycling, especially in relation to climate change (Williams et al. 2006), drought and water table shifts (Tipping et al. 1999; Worral et al. 2004). In contrast, the influence of biotic factors on peatland C cycling, including the potential effects of changes in biodiversity due to land use, remains relatively unexplored (see Ward et al. 2007). Actinobacteria are a functionally varied group of bacteria (Rheims et al. 1996) which are thought constitute an important component of the peat microbial community both in terms of diversity and abundance (Dedysh et al. 2006; Jaatinen et al. 2007). The suite of enzymes produced by actinobacteria, in vitro, include those that degrade structural plant polymers such as lignin and cellulose and the highly recalcitrant organic macromolecules that characterise peats (Hasegawa et al. 2006), yet their role in peatland carbon dynamics remains largely unexplored. Actinobacteria have been identified as both leaf and root endophytes (e.g. Coombs & Franko 2003; Hasegawa et al. 2006) and recent studies have reported that actinobacteria are amongst the endophytes of Sphagnum (Opelt et al. 2007). The antimicrobial properties of peat are legendary and the use of Sphagnum mosses as wound dressings is well documented (Varley & Barnett 1987). The capacity of actinobacteria (e.g. members of the spore-forming actinomycetes) to produce antibiotic secondary metabolites is also well known (see Strobel 2003; Hasegawa et al. 2006) and recent findings have confirmed the antifungal activity of two actinobacterial isolates (Opelt et al. 2007). Actinobacteria, therefore, are not only abundant and active but may also have an inhibitory role on other microbiota involved in decomposition processes, and may hence play a role in microbial competition for carbon and nutrients. Our recent studies provide evidence that changes in peatland plant community composition have a strong influence on soil microbial properties and carbon dynamics (Ward et al., 2007). We therefore propose that changes in plant diversity and composition will similarly be an important determinant of Actinobacteria abundance and diversity, and their functional role in peatland ecosystem carbon cycling. This studentship will build on existing field manipulation experiments to test the following hypotheses: i) That the diversity and activity of actinobacteria in peatland is influenced by differences in plant community composition and diversity; and ii) That the production of antibiotic secondary metabolites by the actinobacterial population in peatlands confers a competitive advantage over other microbes especially fungi. The student will focus research at two experimental sites at the Moorhouse National Nature Reserve Blanket Peatland, where the vegetation is dominated by Calluna vulgaris (L.), Eriophorum sp. Sphagnum sp. and other bryophytes typical of UK upland peat.