Recent studies demonstrate that the dissolved iron in seawater is bound to strong organic complexes that have stability constants comparable to those of microbial iron chelates (siderophores). We investigated iron acquisition by 7 strains of heterotrophic marine bacteria using siderophores as a model for the natural iron-binding ligands. Siderophores were detected in the supernatants of 4 strains. All strains utilized iron bound to siderophores regardless of whether they produced their own. The majority took up iron bound to the fungal siderophore desferrioxamine B (dfoB). Over half also utilized iron bound to strain Neptune's siderophore, nep-L, while iron bound to pwf-L was available solely to the producing strain, Pwf3. Uptake rates of Fe-siderophores were similar among iron-limited strains and among ligands. Transport of Fe-dfoB in Neptune was enhanced 20 times by iron limitation. The half-saturation constant of Fe-dfoB transport was 15 nM, the lowest reported for Fe-siderophore transport in microorganisms. In contrast, uptake of inorganic iron (Fe' ) by iron-limited Neptune did not saturate at the highest concentration tested and was not upregulated under iron stress. This suggests that Fe ' uptake occurs by simple diffusion through the outer membrane. / Strain Lmg1, the sole catechol producer, did not take up iron bound to exogenous siderophores (dfoB, pwf-L, or nep-L). However, it utilized iron bound to its own ligand and, possibly, iron bound to the synthetic chelator EDTA. Transport of Fe' by iron-limited Lmg1 was 10 times higher than in the other strains and was upregulated 46 times in low iron conditions. The results suggest iron transport in Lmg 1 may be mediated by surface-associated catechol siderophores that scavenge inorganic ferric species as well as iron bound to weaker complexes, such as EDTA. This study elucidates the importance of siderophores in iron transport by heterotrophic marine bacteria. (Abstract shortened by UMI.)

Thesis (M. Sc.)--Memorial University of Newfoundland, 1997. / Restricted until November 1998. Bibliography: leaves 123-137.

No description available.

Characterizing dissolved organic matter (DOM) composition remains a major unresolved problem in aquatic ecology. "Tryptophan-like" dissolved organic matter fluorescence (FDOM) was found to be a much better predictor of heterotrophic bacterial metabolism in 28 Quebec lakes than dissolved organic carbon (DOC), describing 52, 44, 51 and 55% of the variability in bacterial production (BP), bacterioplankton respiration (BR), total bacterial carbon consumption (TBCC), and total plankton community respiration (CR), respectively. In addition, the study provides indirect support for the view that FDOM represents a product of bacterial activity, rather than a bioavailable substrate. This is the first field study to show that fluorescence spectroscopy can be used to characterize an aspect of DOM composition that is related to bacterial metabolism, and provides results that encourage further exploration of the potential uses of DOM fluorescence spectroscopy as a predictive tool.

Thesis (M.S.)--Mississippi State University. Department of Biological Sciences. / Title from title screen. Includes bibliographical references.

No description available.

Thesis (S.M.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Biology; and the Woods Hole Oceanographic Institution), 2008. / Includes bibliographical references (p. 54-59). / (cont) An increased understanding of heterotrophic bacterial strategies for acquiring nutrients and trace elements is critical for elucidating their impact on biogeochemical cycling in the ocean. It is estimated that iron is a limiting nutrient for phytoplankton growth in over 30% of the open ocean, but still little is known about bacterial strategies for iron acquisition. Siderophore (Fe ligand) production by bacteria may play a major role in influencing the bioavailability of iron in the ocean. Despite the importance of siderophores in the environment, only limited information from a select group of bacteria is available. On a cruise through the Costa Rica Dome (CRD) upwelling region in July 2005, a library of 867 isolates from five depth profiles inside and outside of the dome was obtained and screened for siderophore production using the Chrome Azurol-S (CAS) assay. Phylogenetic affiliation of 134 isolates was determined by sequencing the 16s rDNA gene, and determined that gamma proteobacteria such as Alteromonas, Pseudoalteromonas, Halomonas, and Marinobacter dominated the collection, while alpha-proteobacteria such as Roseobacter were also represented. The isolates obtained from stations in the CRD showed greater siderophore-producing capabilities between 55m and 100m while strains isolated from outside the CRD had shallower peak (-8-35m) production. Functional group determination showed that hydroxamate production dominated from 50-150m, while hydroxamate and catechol production is roughly equal in shallower waters. By characterizing the siderophores produced by these isolates and determining the genetic make-up of the population, these findings further our understanding of how heterotrophic microbes affect biogeochemical processes and the competitive nature of nutrient acquisition. / by Whitney B. Krey. / S.M.

The $ sp3$H thymidine incorporation (TTI) method has been frequently used to estimate benthic bacterial production rates in well oxygenated marine and river sediments, but not in the frequently more reduced lake sediments. In chapter 1, I evaluate the published sediment production literature and examine useful predictors of in situ bacterial production in mostly marine and riverine sediments. In chapters 2 and 3, I estimated and compared benthic production rates by TTI, frequency of dividing cells (FDC), the dilution method (DIL) and sediment respiration (SR) in 13 Quebec lakes to assess the reliability of the TTI based production rates. The TTI method was first calibrated, but despite keeping incubation times short and at in situ temperature, using optimal sediment volumes to saturate $ sp3$H thymidine (TdR) uptake rates, and correcting production rates for $ sp3$H-DNA recovery efficiencies, only a maximum of 10% of $ sp3$H TdR was incorporated into DNA and only extracellular isotope dilution could be accounted for (chapter 2). Most problematic, however, is the increasing presence of active bacteria unable to take up and incorporate TdR as lake sediments become more reduced (chapter 3). TTI based results are also not nearly as well correlated to environmental factors as those obtained from SR. (Abstract shortened by UMI.)

No description available.

Pelagic aggregates function as biological carbon pumps for transporting fixed organic carbon to sediments. In iron-rich (ferruginous) lakes, photoferrotrophic and chemolithoautotrophic bacteria contribute to CO2 fixation by oxidizing reduced iron, leading to the formation of iron-rich pelagic aggregates (iron snow). The significance of iron oxidizers in carbon fixation, their general role in iron snow functioning and the flow of carbon within iron snow is still unclear. Here, we combined a two-year metatranscriptome analysis of iron snow collected from an acidic lake with protein-based stable isotope probing to determine general metabolic activities and to trace 13CO2 incorporation in iron snow over time under oxic and anoxic conditions. mRNA-derived metatranscriptome of iron snow identified four key players (Leptospirillum, Ferrovum, Acidithrix, Acidiphilium) with relative abundances (59.6–85.7%) encoding ecologically relevant pathways, including carbon fixation and polysaccharide biosynthesis. No transcriptional activity for carbon fixation from archaea or eukaryotes was detected. 13CO2 incorporation studies identified active chemolithoautotroph Ferrovum under both conditions. Only 1.0–5.3% relative 13C abundances were found in heterotrophic Acidiphilium and Acidocella under oxic conditions. These data show that iron oxidizers play an important role in CO2 fixation, but the majority of fixed C will be directly transported to the sediment without feeding heterotrophs in the water column in acidic ferruginous lakes.