Publications

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2008
Dupont, CL, Barbeau K, Palenik B.  2008.  Ni uptake and limitation in marine Synechococcus strains. Applied and Environmental Microbiology. 74:23-31.   10.1128/aem.01007-07   AbstractWebsite

Ni accumulation and utilization were studied in two strains of marine Synechococcus, isolated from both coastal (CC9311; clade I) and open-ocean (WTH8102; clade III) environments, for which complete genome sequences are available. Both strains have genes encoding an Ni-containing urease and when grown on urea without Ni become Ni-N colimited. The Ni requirements of these strains also depend upon the genomic complement of genes encoding superoxide dismutase (SOD). WH8102, with a gene encoding only an Ni-SOD, has a novel obligate requirement for Ni, regardless of the N source. Reduced SOD activity in Ni-depleted cultures of VM8102 supports the link of this strain's Ni requirement to Ni-SOD. The genome of CC9311 contains a gene for a Cu/Zn-SOD in addition to a predicted pair of Ni-SODs, yet this strain cannot grow without Ni on NO3- and can grow only slowly on NH4+ without Ni, implying that the Cu/Zn-SOD cannot completely replace Ni-SOD in marine cyanobacteria. CC9311 does have a greater tolerance for Ni starvation. Both strains increase their Ni uptake capabilities and actively bioconcentrate Ni in response to decreasing extracellular and intracellular Ni. The changes in Ni uptake rates were more pronounced in WH8102 than in CC9311 and for growth on urea or nitrate than for growth on ammonia. These results, combined with an analysis of fully sequenced marine cyanobacterial genomes, suggest that the growth of many marine Synechococcus and all Prochlorococcus strains is dependent upon Ni.

2010
Dupont, CL, Buck KN, Palenik B, Barbeau K.  2010.  Nickel utilization in phytoplankton assemblages from contrasting oceanic regimes. Deep-Sea Research Part I-Oceanographic Research Papers. 57:553-566.   10.1016/j.dsr.2009.12.014   AbstractWebsite

In most oceanic environments, dissolved nickel (Ni) concentrations are drawn clown in surface waters with increasing concentrations at depth, implying a role for biology in the geochemical distribution of Ni Studies with phytoplankton isolates from the surface ocean have established the biochemical roles of Ni in the assimilation of urea and oxidative defense To determine if these requirements are relevant in natural marine planktonic assemblages, bottle-based fertilization experiments were used to test the effects of low-level additions of Ni. urea, or both Ni and urea to surface waters at several locations offshore of Peru and California, as well as in the Gulf of California Urea and Ni(+) urea additions consistently promoted phytoplankton growth relative to control and +Ni treatments, except in a coastal upwelling site and Peruvian water. No effect was observed in the upwelling site, but in Peruvian waters urea additions resulted in increased phytoplankton pigments and phosphate drawdown only when Ni was added concurrently, suggesting a biochemically dependent Ni-urea colimitation In the Gulf of California, Ni additions without urea resulted in increased abundances of cyanobacteria, picoeukaryotes, and the corresponding pigments As urea additions showed the overall phytoplankton community was also urea-limited, it appears that the cyanobactena and potentially the picoeukaryotes were colimited by Ni and urea in a biochemically independent fashion. In parallel, radiotracer-based uptake experiments were used to study the kinetics and spatial variation of biological Ni assimilation. In these experiments, the added radiotracer rarely equilibrated with the natural Ni present, precluding estimates a determination of in situ Ni uptake rates and suggesting that much of the natural Ni was not bioavailable. The lack of equilibration likely did not preclude the measurement of community Ni uptake kinetics, nor the comparison of measured rates between locations The highest V(max)K(p)(-1) values, which reflect a competitive advantage in Ni acquisition at low concentrations, were observed in stratified nitrogen-deplete communities, potentially linking Ni and nitrogen biogeochemistry in a manner consistent with the biochemical utilization of Ni. Overall, uptake rates were higher in the euphotic rather than non-euphotic zone communities, directly reconciling the nutrient-like depth profile of Ni The Ni uptake rates observed at the nitrate-replete Fe-deplete Peru stations were an order of magnitude lower than the other sites This result agrees with calculations suggesting that saturation of the cell surface with Ni and iron (Fe) transporters may limit uptake rates in low Fe waters. (C) 2010 Elsevier Ltd. All rights reserved