The role of computer keyboards used by students of a metropolitan university as reservoirs of antibiotic-resistant staphylococci was determined. Putative methicillin (oxacillin)-resistant staphylococci isolates were identified from keyboard swabs following a combination of biochemical and genetic analyses. Of 24 keyboards surveyed, 17 were contaminated with staphylococci that grew in the presence of oxacillin (2 mg l À1 ). Methicillin (oxacillin)-resistant Staphylococcus aureus (MRSA), -S. epidermidis (MRSE) and -S. hominis (MRSH) were present on two, five and two keyboards, respectively, while all three staphylococci co-contaminated one keyboard. Furthermore, these were found to be part of a greater community of oxacillin-resistant bacteria. Combined with the broad user base common to public computers, the presence of antibiotic-resistant staphylococci on keyboard surfaces might impact the transmission and prevalence of pathogens throughout the community.

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Acetochlor is the third most frequently detected herbicide in natural waters; however, it is unknown if exposure to environmentally relevant concentrations of acetochlor will impact bacterial community structure and function. This study examined the impact of acetochlor on freshwater heterotrophic bacteria number, and community structure and function using direct counting, community level physiological profiling (CLPP) and denaturing gradient gel electrophoresis (DGGE) analysis. Acetochlor concentration did not appear to correlate with the number of total (P ¼ 0.69) and viable (P ¼ 0.80) bacteria, even at concentrations up to 500 lg l À1 . However, CLPP indicated that acetochlor increased functional diversity as shown by (i) an increase in the number of carbon sources utilized by the microbial community, relative to nonexposed controls and (ii) increased functional evenness within the heterotrophic bacterial community. Conversely, DGGE fingerprints suggested that exposure to acetochlor generally decreased the community complexity, as the average number of DGGE bands in most treatments was significantly less than in the control treatment. Cluster analysis of DGGE fingerprints revealed three distinct, dose-dependent clusters (i) communities exposed to 0, 1 and 5 lg l À1 ; (ii) 50 and 100 lg l À1 and (iii) 500 lg l À1, indicating a relationship between acetochlor concentration bacterial community changes. This study indicated that while exposure to environmentally relevant concentrations of acetochlor resulted in no significant impact to the number of freshwater bacteria, impacts to the function and structure of the community were revealed by adopting a multiphasic approach.

Our understanding of the effects of elevated atmospheric CO 2 , singly and in combination with other environmental changes, on plant-soil interactions is incomplete. Elevated CO 2 effects on C 4 plants, though smaller than on C 3 species, are mediated mostly via decreased stomatal conductance and thus water loss. Therefore, we characterized the interactive effect of elevated CO 2 and drought on soil microbial communities associated with a dominant C 4 prairie grass, Andropogon gerardii Vitman. Elevated CO 2 and drought both affected resources available to the soil microbial community. For example, elevated CO 2 increased the soil C:N ratio and water content during drought, whereas drought alone decreased both. Drought significantly decreased soil microbial biomass. In contrast, elevated CO 2 increased biomass while ameliorating biomass decreases that were induced under drought. Total and active direct bacterial counts and carbon substrate use (overall use and number of used sources) increased significantly under elevated CO 2 . Denaturing gradient gel electrophoresis analysis revealed that drought and elevated CO 2 , singly and combined, did not affect the soil bacteria community structure. We conclude that elevated CO 2 alone increased bacterial abundance and microbial activity and carbon use, probably in response to increased root exudation. Elevated CO 2 also limited drought-related impacts on microbial activity and biomass, which likely resulted from decreased plant water use under elevated CO 2 . These are among the first results showing that elevated CO 2 and drought work in opposition to modulate plant-associated soil-bacteria responses, which should then influence soil resources and plant and ecosystem function.Key words: denaturing gradient gel electrophoresis; drought; elevated CO 2 ; soil microbial communities. During the last nine decades, the atmospheric concentration of CO 2 has increased by 36%, primarily as a result of anthropogenic activities (IPCC 2007). Increased atmospheric CO 2 concentration and related environmental changes (e.g. warming and decreased/increased precipitation) can influence the biological processes of plants and soil microorganisms inhabiting diverse ecosystems (Zak et al. 1993(Zak et al. , 2000 Kandeler et al. 1998 C 3 and C 4 photosynthetic metabolism, though photosynthetic and growth increases are generally larger in C 3 species (e.g., Sage and Monson 1999; Ehleringer et al. 2002;Wang et al. 2008 and references therein). In C 3 species, increased growth under elevated CO 2 is primarily due to decreased photorespiration (photosynthetic fixation of O 2 rather than CO 2 ), while in C 4 species, increased growth under elevated CO 2 is primarily due to decreased stomatal conductance and transpiration, which decreases soil water use (this also occurs in C 3 species).As with most terrestrial ecosystems, grasslands will be impacted by future global environmental and climate changes, including elevated CO 2 (Fay et al. 2003), and this will have importance to the global eco...

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