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To address how phytoplankton in the Great Lakes respond to macro- and micronutrients, we conducted a bottle incubation enrichment experiment using water collected from blooming (Maumee Bay and Fox River) and non-blooming sites (Detroit River and Ford River) in Lakes Erie and Michigan, respectively, during late summer. Surface water from these locations was collected and taken to Kent State University either via overnight shipping (Lake Michigan sites) or driven directly after collection (Lake Erie sites). Chlorophyll a (an index of overall biomass), community composition and toxicity were all measured as responses to treatments of labile inorganic nitrogen (N), phosphorus (P) and a mixture of micronutrients (chemical symbols: Fe, Mn, Mo, Ni, Zn). 

Metals are used in primary producer metabolic pathways, such as photosynthesis and the acquisition of macronutrients nitrogen (N) and phosphorus (P), yet we often do not know their potential as limiting nutrients in freshwaters. In the Great Lakes, metals have sometimes been identified as limiting the acquisition of macronutrients, mostly in off-shore waters that are relatively isolated from tributary inputs and sediment interactions. We hypothesized that another area where metals might be important was within harmful algal blooms (HABs). Harmful algal blooms are more likely to occur where N and P loads are elevated due to human activities, but short-term growth assays still often find summer bloom communities are N or P limited due to high biotic demand. This high biotic is associated with rapid nutrient recycling which may increase demand for trace metals beyond the available supply. A relatively common cyanotoxin (microcystin) has also been hypothesized to have a role in trace metal management, so trace metal demand may also influence the toxicity of bloom communities. Here, we used nutrient diffusing substrates to measure the magnitude of macronutrient and trace metal effects on growth and toxicity of biofilms suspended in 10 nearshore sites in Lake Michigan and Lake Erie (5 with and 5 without perennial HABs). We measured microcystin, chlorophyll a, ash free dry mass and community composition on the experimental biofilms. 

Arsenic is a toxic metalloid with differential biological effects, depending on speciation and concentration. Trivalent arsenic (arsenite, AsIII) is more toxic at lower concentrations than the pentavalent form (arsenate, AsV). In E. coli, the proteins encoded by the arsRBC operon are the major arsenic detoxification mechanism. Our previous transcriptional analyses indicate broad changes in metal uptake and regulation upon arsenic exposure. Currently, it is not known how arsenic exposure impacts the cellular distribution of other metals. This study examines the metalloproteome of E. coli strains with and without the arsRBC operon in response to sublethal doses of AsIII and AsV. Size exclusion chromatography coupled with inductively coupled plasma mass spectrometry (SEC-ICPMS) was used to investigate the distribution of five metals (56Fe, 24Mg, 66Zn, 75As, and 63Cu) in proteins and protein complexes under native conditions. Parallel analysis by SEC-UV-Vis spectroscopy monitored the presence of protein cofactors. Together, these data reveal global changes in the metalloproteome, proteome, protein cofactors, and soluble intracellular metal pools in response to arsenic stress in E. coli. This work brings to light one outcome of metal exposure and suggests that metal toxicity on the cellular level arises from direct and indirect effects.