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The photosynthetic amoeba, Paulinella provides a recent (ca. 120 Mya) example of primary plastid endosymbiosis. Given the extensive data demonstrating host lineage‐driven endosymbiont integration, we analysed nuclear genome and transcriptome data to investigate mechanisms that may have evolved in Paulinella micropora KR01 (hereinafter, KR01) to maintain photosynthetic function in the novel organelle, the chromatophore. The chromatophore is of α‐cyanobacterial provenance and has undergone massive gene loss due to Muller's ratchet, but still retains genes that encode the ancestral α‐carboxysome and the shell carbonic anhydrase, two critical components of the biophysical CO2 concentrating mechanism (CCM) in cyanobacteria. We identified KR01 nuclear genes potentially involved in the CCM that arose via duplication and divergence and are upregulated in response to high light and downregulated under elevated CO2. We speculate that these genes may comprise a novel CO2 delivery system (i.e., a biochemical CCM) to promote the turnover of the RuBisCO carboxylation reaction and counteract photorespiration. We posit that KR01 has an inefficient photorespiratory system that cannot fully recycle the C2 product of RuBisCO oxygenation back to the Calvin‐Benson cycle. Nonetheless, both these systems appear to be sufficient to allow Paulinella to persist in environments dominated by faster‐growing phototrophs. [ABSTRACT FROM AUTHOR]

Sources of methylmercury (MeHg) in adult Pacific bluefin tuna (Thunnus orientalis, PBT) from the western North Pacific Ocean (WPO) were examined using mercury stable isotopes. Significant increases in δ202Hg and Δ199Hg values with PBT size and age, along with those of potential prey, indicate a shift in the source of MeHg accumulated by PBT as they age. Among adults from the WPO, this shift likely involves greater accumulation of MeHg from epipelagic prey in the Kuroshio extension in large vs. small and medium-sized PBT. For all adults, little MeHg is accumulated in the spawning grounds near Taiwan. Significantly lower Δ199Hg/Δ201Hg ratios in adult PBT and their prey from the WPO than from the central and eastern North Pacific indicate different sources or transformations of MeHg prior to accumulation in the WPO food web than further east. Our results show that MeHg sources to oceanic food webs vary across the North Pacific Ocean and regionally within the WPO. [ABSTRACT FROM AUTHOR]

The mechanisms of carbon concentration in marine diatoms are controversial. At low CO2, decreases in O2 evolution after inhibition of phosphoenolpyruvate carboxylases ( PEPCs), and increases in PEPC transcript abundances, have been interpreted as evidence for a C4 mechanism in Thalassiosira pseudonana, but the ascertainment of which proteins are responsible for the subsequent decarboxylation and PEP regeneration steps has been elusive., We evaluated the responses of T. pseudonana to steady-state differences in CO2 availability, as well as to transient shifts to low CO2, by integrated measurements of photosynthetic parameters, transcript abundances and quantitative proteomics., On shifts to low CO2, two PEPC transcript abundances increased and then declined on timescales consistent with recoveries of Fv/ Fm, non-photochemical quenching ( NPQ) and maximum chlorophyll a-specific carbon fixation ( Pmax), but transcripts for archetypical decarboxylation enzymes phosphoenolpyruvate carboxykinase ( PEPCK) and malic enzyme ( ME) did not change. Of 3688 protein abundances measured, 39 were up-regulated under low CO2, including both PEPCs and pyruvate carboxylase ( PYC), whereas ME abundance did not change and PEPCK abundance declined., We propose a closed-loop biochemical model, whereby T. pseudonana produces and subsequently decarboxylates a C4 acid via PEPC2 and PYC, respectively, regenerates phosphoenolpyruvate ( PEP) from pyruvate in a pyruvate phosphate dikinase-independent (but glycine decarboxylase ( GDC)-dependent) manner, and recuperates photorespiratory CO2 as oxaloacetate ( OAA). [ABSTRACT FROM AUTHOR]

The concentrations of Ag, Cd, Cu, Hg(II), monomethylmercury (MeHg), Pb, and Zn were measured and modeled in calanoid copepods collected from the Hudson River plume in April 2005 and May 2006. Copepods in the buoyant plume were significantly (p < 0.05) enriched in Ag, Cu, Pb, Zn, and MeHg (2- to 25-fold), but depleted in Cd (by 25-40%) relative to oceanic copepods. Median burdens of Ag, Cu, and Hg(II) differed in plume copepods collected in April 2005 and May 2006 by factors of 1.5 to 3, reflecting the influence of river discharge and associated physical processes on plankton dynamics and metal bioaccumulation. Only the concentrations of Cu and Zn in plume copepods clearly showed the expected trend of highest levels near the mouth of the Hudson River and lower levels offshore. Spatial trends in concentrations of Ag and Hg(II) in plume copepods were strikingly different from those in suspended particles and the dissolved phase, apparently reflecting differences in metal bioavailability because of shifts in available food types. Modeled concentrations of Cd, Cu, Pb, and Zn in plume copepods were within less than a factor of two of measured values, but model results showed that Hg(II) was less bioavailable, and Ag and MeHg were more bioavailable in the Hudson River plume than laboratory results would predict. Zooplankton from urban river plumes may accumulate potentially toxic levels of trace metals or act as a trophic link between metal contamination in polluted estuaries and pelagic ecosystems. [ABSTRACT FROM AUTHOR]

Metabolic responses to the subacute toxicities (non-growth-rate inhibiting) of Cd, Cu, and Zn were measured in the coastal marine diatom Thalassiosira weissflogii using calorespirometry. Respiratory heat production and oxygen consumption rates were measured in diatom cells grown with concentrations of Cd2+ (10-12 to 10-8 M), Cu2+ (10-13.8 to 10-9.8 M), and Zn2+ (10-10.9 to 10-6.9 M) that are typical of urban and suburban coastal waters. These trace metals did not significantly inhibit diatom growth rates in high-nutrient, high-light laboratory cultures except for the highest concentrations of Cd (Cd2+ = 10-8 M) and Zn (Zn2+ = 10-6.9 M). Respiratory heat rates in cells grown with elevated, but on-growth-rate-inhibiting free Cu2+ ion concentrations (10-11.8 to 10-9.8 M) were up to 40% higher and oxygen consumption rates were 50 to 75% lower than control ([Cu2+] = 10-10.8 M) cells indicating a subacute depression of respiratory efficiency in Cu-exposed cells. Exposure to elevated free Cd2+ concentrations (10-10 to 10-8 M) caused dramatic short-term (hours) increases (five- to eight-fold) in respiratory oxygen consumption rates, which returned to normal in acclimated cells, suggesting a transient disruption of metabolism upon Cd exposure. Zinc did not significantly affect either respiratory parameter up to a free Zn concentration of 10-7.9 M, above which diatom growth rate was significantly reduced. The subacute toxic effects of Cd and Cu were more pronounced in low Mn than in Mn-replete cells, consistent with proposed Mn- Cd, -Cu antagonisms in marine phytoplankton. The range of free Cu2+ ion concentrations in coastal waters is similar to that found to cause a decrease in respiratory efficiency in T. weissflogii, th... [ABSTRACT FROM AUTHOR]

We measured short-term uptake rates of copper using the gamma-emitting radioisotope 67Cu in seven algal species in natural and artificial seawater. Cellular net uptake of Cu was typically rapid over periods of 2-20 min. Net uptake ceased after about 60 min. The most copper-sensitive species examined, Synechococcus sp., exhibited 2-3 orders of magnitude higher carbon and surface-area-normalized Cu-accumulation rates (46 µmol Cu mol C-1 min-1 and 1,100 zmol Cu µm-2 min-1) (zmol X 10-21 moles) than those measured in diatoms, chlorophytes, a dinoflagellate, and a coccolithophore. Cu-accumulation rates for Thalassiosira weissflogii were three times faster in natural seawater than in EDTA-buffered artificial seawater containing an inorganic Cu concentration of 28 pmol L-1. Calculations showing that the diffusive flux of inorganic Cu was insufficient to account for observed short-term uptake rates suggest that some of the Cu bound to naturally occurring organic ligands is released through the rapid dissociation of those complexes in the cell's boundary layer. [ABSTRACT FROM AUTHOR]