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A study was conducted to assess the effects of predicted climate change on seedling emergence, growth, and survival for the federally listed threatened species Cirsium pitcheri in the region proximal to Chicago, Illinois, U.S.A. Three geographically distant extant populations that could potentially serve as donors to re- introduced Illinois populations were tested to determine the influence of local adaptation on seed response to climate scenarios at two future time points. For all three populations, temperature was shown to be the most critical factor impacting future growth. All populations performed worst at the 2095 temperature for four measured growth metrics: length of longest adult leaf, number of adult leaves, dry shoot mass, and dry root mass. Growth performance at the 2095 conditions did not correlate with climate familiarity but did reflect the genetic diversity of the parent population. Predicted changes in average precipitation did not produce a significant effect on any growth metric, possibly reflecting a limitation in the study conditions. Seedling emergence and survival were tied to seed mass, a trait influenced by maternal effects and correlated with the level of inbreeding depression in the parent population. These results suggest managing populations to maintain high genetic diversity could be an important factor in tolerating temperature stress associated with climate change.

Copper homeostasis in bacteria is challenged by periodic elevation of copper levels in the environment, arising from both natural sources and human inputs. Several mechanisms have evolved to efflux copper from bacterial cells, including the cus (copper sensing copper efflux system), and pco (plasmid-borne copper resistance system) systems. The genes belonging to these two systems can be physically clustered in a Copper Homeostasis and Silver Resistance Island (CHASRI) on both plasmids and chromosomes in Enterobacteria. Increasing use of copper in agricultural and industrial applications raises questions about the role of human activity in the evolution of novel copper resistance mechanisms. Here we present evidence that CHASRI emerged and diversified in response to copper deposition across aerobic and anaerobic environments. An analysis of diversification rates and a molecular clock model suggest that CHASRI experienced repeated episodes of elevated diversification that could correspond to peaks in human copper production. Phylogenetic analyses suggest that CHASRI originated in a relative of Enterobacter cloacae as the ultimate product of sequential assembly of several pre-existing two-gene modules. Once assembled, CHASRI dispersed via horizontal gene transfer within Enterobacteriaceae and also to certain members of Shewanellaceae, where the original pco module was replaced by a divergent pco homolog. Analyses of copper stress mitigation suggest that CHASRI confers increased resistance aerobically, anaerobically, and during shifts between aerobic and anaerobic environments, which could explain its persistence in facultative anaerobes and emergent enteric pathogens.

Methionine-rich motifs have an important role in copper trafficking factors, including the CusF protein. Here we show that CusF uses a new metal recognition site wherein Cu(I) is tetragonally displaced from a Met2His ligand plane toward a conserved tryptophan. Spectroscopic studies demonstrate that both thioether ligation and strong cation-pi interactions with tryptophan stabilize metal binding. This novel active site chemistry affords mechanisms for control of adventitious metal redox and substitution chemistry.