![pathfinder microcosm pathfinder microcosm](https://www.nadadventist.org/sites/default/files/2019-08/web%20thumb%20crop%202019%20oshkosh%20bmx%20bike%2048546818571_181f2f05a8_k.jpg)
Other studies have shown that soil microbial communities mediate Au mobilisation, and that underlying Au deposits may influence microbial communities ( Reith and McPhail, 2006 Reith and Rogers, 2008). One study of soils overlying a base metal (Cu, Pb and Zn) deposit in Western Australia has shown that the solubilisation, transport and deposition of metals are mediated by resident plant and microbial communities, in turn altering the structure of microbial communities in the metal-rich soils overlying the deposit ( Wakelin et al., 2012b). In contrast, few studies have looked at natural systems in which physical and biogeochemical processes have formed ‘enrichment haloes’ of metals in soils overlying mineral deposits ( Aspandiar et al., 2008). Similarly, amendment of soils with Cu, Pb, Zn and Cd strongly influences resident bacterial communities ( Bååth, 1989 Abaye et al., 2005 Wakelin et al., 2010a, 2010b).
![pathfinder microcosm pathfinder microcosm](https://1.bp.blogspot.com/-aQGtSlcrmgA/V-QX1FSIeHI/AAAAAAAANJ4/TNEP6vyPKJ8uPM7UvsDZ8K25TU7AbXYAQCLcB/s1600/TMG-Crusaders-box-flat.png)
High concentrations of metals, for example in soils exposed to industrial pollution or mining, substantially alter microbial communities ( Baker and Banfield 2003 Hu et al., 2007 Kock and Schippers, 2008 Denef et al., 2010). However, these are likely to be second order influences within ecosystems, which are predominantly driven by geogenic factors. As geogenic influences are likely to develop over extended ‘geologic’ periods of time, their effects may be masked by ‘short term’ changes in vegetation, landuse or anthropogenic influences ( Viles, 2011, in press). In contrast, the importance of geogenic drivers, comprising geomorphological, geological and geochemical factors such as the landform, the underlying lithology and the presence of buried mineral deposits (expressed in overlying soils as elevated concentrations of mobile metals) are less well understood ( Viles, 2011, in press). Environmental factors, for example, soil-type, vegetation, landuse and associated physicochemical parameters, for example, C– N–, water content and pH, have been linked to soil microbial structures and activities ( Acosta-Martinez et al., 2008 Lauber et al., 2008 Wakelin et al., 2008 Drenovsky et al., 2010). Difficulties arise because of the complexity of soil ecosystems, where large number of niches provide for high levels of species diversity and complex ecosystem interactions ( Fierer and Jackson, 2006).
![pathfinder microcosm pathfinder microcosm](http://www.jeff-hester.com/wp-content/uploads/2020/06/COVID-US-768x493.jpg)
#PATHFINDER MICROCOSM DRIVERS#
Identifying drivers of microbial community structures in soils is challenging. In particular, the landform, which is a crucial factor in determining soil geochemistry, strongly affected microbial community structures. These data help establish key links between geogenic factors and the phylogeny and function within soil microbial communities. For example, genes that hybridised with metal-resistance genes copA, chrA and czcA of a prevalent aurophillic bacterium, Cupriavidus metallidurans CH34, occurred only in auriferous soils. Analyses of potential function (GeoChip) revealed higher abundances of metal-resistance genes in metal-rich soils. PhyloChip analyses revealed a greater abundance and diversity of Alphaproteobacteria (especially Sphingomonas spp.), and Firmicutes ( Bacillus spp.) in Au-containing and Au(III)-amended soils. The strongest responses to these factors, and to amendment with soluble Au(III) complexes, was observed in bacterial communities. Microbial communities differed significantly between landforms, soil horizons, lithologies and also with the occurrence of underlying Au deposits. Geogenic factors of soils were determined using lithological-, geomorphological- and soil-mapping combined with analyses of 51 geochemical parameters. Field-fresh soils and soils incubated with soluble Au(III) complexes were analysed using three-domain multiplex-terminal restriction fragment length polymorphism, and phylogenetic (PhyloChip) and functional (GeoChip) microarrays. Links between microbial community assemblages and geogenic factors were assessed in 187 soil samples collected from four metal-rich provinces across Australia.