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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 (PhyloChip). The dominant taxa at the site were Proteobacteria, Actinobacteria and Firmicutes; however, 37 phyla were detected. The most responsive taxa to variation in E.C. was Acidobacteria (negative correlation). Patterns of heterotrophic processes (BioLog 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.

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Alternatives for control of soil-inhabiting pests are needed due to the phase-out of methyl bromide. One possible alternative is using the pesticidal properties of compounds released by macerated Brassica tissues. In this study, larvae of masked chafer beetles (Cyclocephala spp.) were placed in soil amended with Brassica juncea L. (PI 458934) tissue. Allyl isothiocyanate (AITC) levels were positively correlated to larval mortality, with the 8% B. juncea treatment resulting in 100% larval mortality with an average AITC concentration of 11.4 mg per liter of soil atmosphere. Although B. juncea produces high levels of AITC, the mass of tissue required for significant insecticidal activity against Cyclocephala spp. also is high, between 4 and 8% of soil mass for this plant accession. Accepted for publication 23 May 2002. Published 10 June 2002.