Tracking Changes in Bioavailable Fe Within High-Nitrate Low-Chlorophyll Oceanic Waters: A First Estimate Using a Heterotrophic Bacterial Bioreporter

It is conventional knowledge that heterotrophic bacteria play a key role in the biogeochemical cycling of oceanic carbon. However, only recently has their role in marine iron ( Fe) biogeochemical cycles been examined. Research during this past decade has demonstrated an inextricable link between Fe chemistry and the biota, as \u3e99% of Fe in marine systems is complexed to organic chelates of unknown but obviously biotic origin. Here we present a novel approach to assess and compare Fe bioavailability in low Fe HNLC waters using a bioluminescent bacterial reporter that quantitatively responds to the concentration of bioavailable Fe by producing light. Originally tested in freshwater environments, this study presents the first characterization of this halotolerant reporter organism in a defined seawater medium and then subsequently in marine surface waters. Laboratory characterizations demonstrate that this reporter displays a dose-dependent response to Fe availability in our defined marine medium. Field tests were performed during the 10-day mesoscale FeCycle experiment ( February 2003) in the Pacific sub-Antarctic high-nitrate low-chlorophyll region. Data from both biogeochemical measures and bioreporter assays are provided which describe how the bioreporter detected changes in Fe bioavailability that occurred during a natural shift in ambient dissolved Fe concentrations (similar to 40 pM). Our data explore the use of heterotrophic bioluminescent reporters as a comparable tool for marine ecosystems and demonstrate the potential utility of this tool in elucidating the relationship between Fe bioavailability and Fe chemistry in complex marine systems

Basin scale survey of marine humic fluorescence in the Atlantic: relationship to iron solubility and H2O2

Iron (Fe) is a limiting nutrient for phytoplankton productivity in many different oceanic regions. A critical aspect underlying iron limitation is its low solubility in seawater as this controls the distribution and transport of iron through the ocean. Processes which enhance the solubility of iron in seawater, either through redox reactions or organic complexation, are central to understanding the biogeochemical cycling of iron. In this work we combined iron solubility measurements with parallel factor (PARAFAC) data analysis of CDOM fluorescence along a meridional transect through the Atlantic (PS ANT XXVI-4) to examine the hypothesis that marine humic fluorescence is a potential proxy for iron solubility in the surface ocean. PARAFAC analysis revealed 4 components, two humic like substances and two protein-like. Overall none of the 4 components were significantly correlated with iron solubility, though humic-like components were weakly correlated with iron solubility in iron replete waters. Our analysis suggests that the ligands responsible for maintaining iron in solution in the euphotic zone are sourced from both remineralisation processes and specific ligands produced in response to iron stress and are not easily related to bulk CDOM properties. The humic fluorescence signal was sharply attenuated in surface waters presumably most likely due to photo bleaching, though there was only a weak correlation with the transient photo product H2O2, suggesting longer lifetimes in the photic zone for the fluorescent components identified here. Key Points: - humic-like components correlated with Fe solubility in iron repleted water - ligands are sourced from remineralisation processes produced to Fe stress - humic flu sharply attenuated in surface waters, but only weak corr. with H2O

Marine and freshwater cyanophages in a Laurentian Great Lake: Evidence from infectivity assays and molecular analyses of g20 genes

While it is well established that viruses play an important role in the structure of marine microbial food webs, few studies have directly addressed their role in large lake systems. As part of an ongoing study of the microbial ecology of Lake Erie, we have examined the distribution and diversity of viruses in this system. One surprising result has been the pervasive distribution of cyanophages that infect the marine cyanobacterial isolate Synechococcus sp. strain WH7803. Viruses that lytically infect this cyanobacterium were identified throughout the western basin of Lake Erie, as well as in locations within the central and eastern basins. Analyses of the gene encoding the g20 viral capsid assembly protein (a conservative phylogenetic marker for the cyanophage) indicate that these viruses, as well as amplicons from natural populations and the ballast of commercial ships, are related to marine cyanophages but in some cases form a unique clade, leaving questions concerning the native hosts of these viruses. The results suggest that cyanophages may be as important in freshwater systems as they are known to be in marine systems. Copyright © 2006, American Society for Microbiology. All Rights Reserved

Determination of bioavailable Fe in Lake Erie using a luminescent cyanobacterial bioreporter

Low Fe bioavailability has been suggested as a potential constraint on primary production In the Great Lakes. Here we report on the use of a cyanobacterlal bioreporter to assess available Fe In Lake Erie during summer and fall field seasons In 2001-02. Bioreporter luminescence was derived from a luclferase reporter controlled by Iron-responsive promoter element isiAB. Filtered (\u3c 0.2 μm) water sampled from the western basin during summer 2001-02 yielded low bioreporter response indicating Fe sufficient conditions [-log [free Fe3+] (pFe) \u3c 20.8]. Likewise, water collected from the eastern basin following autumnal mixing in November 2001 yielded a Fe sufficient bioreporter response. In contrast, surface water collected at pelagic stations located In central and eastern basins during summer 2002 indicated a seasonal depletion of bioavailable Fe. Whereas water sampled from these locations during July and August was characterized as Fe sufficient (pFe \u3c 20.8), samples collected during September elicited a high luminescent response from the bioreporter (pFe \u3e 21). Contrary to the characterization provided by the filtered samples, assay of bioreporter response in unfiltered water conducted during the September 2002 cruise indicated these samples to be Fe sufficient (pFe \u3c 20.6). Although this suggests that the dominant pool of bioavailable Fe is contained in the particulate fraction, we cannot discount the possibility that the bioreporter was rendered Fe sufficient by Fe regenerated predominantly from blore-porter cells themselves. Thus, while it is clear that regenerative processes contribute to the pool of bioavailable Fe, it is equally clear that future efforts using the bioreporter with unfiltered water samples must account for the potential influence of Fe introduced by the added reporter cells

Global-scale processes with a nanoscale drive: the role of marine viruses

4 pages, 1 figureViruses, the smallest and most numerous of all biotic agents, represent the planet’s largest pool of genetic diversity. The sheer abundance of oceanic viruses results in B1029 viral infections per day, causing the release of 108–109 tonnes of carbon per day from the biological pool (Suttle, 2007). Still, how and to what extent virus-mediated nanoscale processes are linked to global-scale biodiversity and biogeochemistry is poorly defined. Recently, two international panels—the EUR- opean network of excellence for OCean Ecosystem ANalysis (EUR-OCEANS) Marine Virus Workshop and the Scientific Committee for Oceanographic Research working group on marine viruses (SCOR WG126) brought together international scientists to focus on these issues and to identify future direc- tions in marine virus research by defining important questions (EUR-OCEANS) and potential practical approaches (SCOR). The present commentary high-lights open questions in marine viral ecology and illustrates how fusions between (meta)genomics and geochemistry may decipher the role of viruses in global-scale processesPeer reviewe