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The abundances of ammonia-oxidising archaea (AOA) and ammonia-oxidising bacteria (AOB) in soils underlying pastures in the south-west of Western Australia (WA) were investigated. samples were collected from irrigated pastures and one unmanaged (driveway) area during December 2009. Archaeal and bacterial ammonia monooxygenase (amoA) genes were quantified using real-time PCR, and the diversity of the archaeal amoA genes was investigated using denaturing gradient gel electrophoresis (PCR-DGGE). AOA amoA gene copies outnumbered AOB in all samples. Numbers ofarchaeal amoA genes ranged from 4.1 E+01 to 1.34E+05 gene copies/ng soil DNA. Bacterial amoA genes were below detection limits at three of the four sample sites and ranged from 8.9E+01 to 6.7E+02 gene copies/rig soil DNA at the remaining site. Potential nitrification rates (PNR) were not correlated with AOA or AOB gene abundance, but high PNR only occurred at the site with measureable numbers of AOB. The DGGE analysis revealed that the AOA community was diverse and variability in banding patterns was significantly affected by both site and depth (P< 0.05). Statistical analysis matching biological variation (AOA amoA genotypes) to environmental variables (BEST analysis) revealed that pH was the key driver of AOA community structure (p-0.72; P = 0.005). Soil pH was also inversely correlated to abundance of AOA amoA genes in soil (p = 0.8; P=0.003). This study has shown that AOA are important members of the nitrogencycling community in acidic WA pasture soils, and likely in the wider agricultural soils of WA. Additional keywords: ammonia oxidation, acidic soils, ammonia-oxidising archaea, ammonia-oxidising bacteria, amoA, nitrification., Introduction The microbially mediated conversion of ammonium-nitrogen (N[H.sup.4.sup.+]-N) to nitrite-N (N[O.sub.2.sup.-]-N) is the first step in the process of nitrification, i.e. the oxidation of N[H.sup.4.sup.+] to nitrate (N[O.sub.3]) (Focht and [...]

Biofilms living on gold (Au) grains play a key role in the biogeochemical cycle of Au by promoting the dispersion of Au via the formation of Au nanoparticles as well as the formation of secondary biomorphic Au. Gold grains from Queensland, Australia, are covered by a polymorphic, organic-inorganic layer that is up to 40 [micro]m thick. It consists of a bacterial biofilm containing Au nanoparticles associated with extracellular polymeric substances as well as bacterioform Au. Focused ion beam (FIB) sectioning through the biofilm revealed that aggregates of nanoparticulate Au line open spaces beneath the active biofilm layer. These aggregates (bacterioform Au type 1) resulted from the reprecipitation of dissolved Au, and their internal growth structures provide direct evidence for coarsening of the Au grains. At the contact between the polymorphic layer and the primary Au, bacterioform Au type 2 is present. It consists of solid rounded forms into which crystal boundaries of underlying primary Au extend, and is the result of dealloying and Ag dissolution from the primary Au. This study demonstrates that (1) microbially driven dissolution, precipitation, and aggregation lead to the formation of bacterioform Au and contribute to the growth of Au grains under supergene conditions, and (2) the microbially driven mobilization of coarse Au into nanoparticles plays a key role in mediating the mobility of Au in surface environments, because the release of nanoparticulate Au upon biofilm disintegration greatly enhances environmental mobility compared to Au complexes only. doi: 10.1130/G31052.1

We investigated bacterial community assemblages and functions down a hill slope contaminated by tailings from a volcanogenic massive sulphide mine in arid Western Australia. Weathering of waste rock, high in S and Fe, had resulted in a varying elemental dispersal down a face of the tailings hill. Bacterial community assemblage, characterised by PCR- DGGE fingerprinting, was significantly associated with electrical conductivity ( E. C.) (ρ = 0.664; P < 0.01). Analysis of mobile salts showed that E. C. values were driven by ionic S, Zn, Cl and Al. The bacterial community assemblage was directly characterised across an E. C. gradient using an oligonucleotide microarray ( Phylo Chip). The dominant taxa at the site were P roteobacteria, A ctinobacteria and F irmicutes; however, 37 phyla were detected. The most responsive taxa to variation in E. C. was A cidobacteria (negative correlation). Patterns of heterotrophic processes ( Bio Log analysis) were also best explained by variation in E. C. (ρ = 0.53; P < 0.01), showing a link between primary mineral weathering by lithotrophic bacteria and abiotic processes, and secondary biogeochemical processes by heterotrophic taxa. These data significantly broaden our knowledge of the bacteria present in metallomorphic ecosystems, establish that mobile phase elements are key drivers of community structure, and that primary biogeochemical cycling is directly influencing other geochemical interactions in the samples. [ABSTRACT FROM AUTHOR]

This study shows that the geogenic factors landform, lithology, and underlying mineral deposits (expressed by elevated metal concentrations in overlying soils) are key drivers of microbial community diversity in naturally metal-rich Australian soils with different land uses, i.e., agriculture versus natural bushland. One hundred sixty-eight soil samples were obtained from two metal-rich provinces in Australia, i.e., the Fifield Au-Pt field (New South Wales) and the Hillside Cu-Au-U rare-earth-element (REE) deposit (South Australia). Soils were analyzed using three-domain multiplex terminal-restriction-fragment-length-polymorphism (M-TRFLP) and PhyloChip microarrays. Geogenic factors were determined using field-mapping techniques and analyses of >50 geochemical parameters. At Fifield, microbial communities differed significantly with geogenic factors and equally with land use (P < 0.05). At Hillside, communities in surface soils (0.03- to 0.2-m depth) differed significantly with landform and land use (P < 0.05). Communities in deeper soils (>0.2 m) differed significantly with lithology and mineral deposit (P < 0.05). Across both sites, elevated metal contents in soils overlying mineral deposits were selective for a range of bacterial taxa, most importantly Acidobacteria, Bacilli, Betaproteobacteria, and Epsilonproteobacteria. In conclusion, long-term geogenic factors can be just as important as land use in determining soil microbial community diversity. [ABSTRACT FROM AUTHOR]