Effects of Copper Availability on the Physiology of Marine Heterotrophic Bacteria

Marine heterotrophic bacteria play a crucial role in the cycling of energy and nutrients in the ocean. Copper (Cu) belongs to the repertoire of essential trace nutrients for bacterial growth, yet physiological responses of marine heterotrophic bacteria to Cu deficiency remain unexplored. Here, we examined these responses in oceanic and coastal isolates of heterotrophic bacteria from ecologically significant microbial clades (Flavobacteriia class from Bacteroidetes phylum, and marine Roseobacter clade within Alphaproteobacteria class and Alteromonadales within Gammaproteobacteria class, both from Proteobacteria phylum). Bacterial growth, Cu quotas (Cu:P), macronutrient content and stoichiometry (cellular C, N, P, S, and C:N, S:P), as well as carbon metabolism (respiration, productivity, carbon demand, growth efficiency) were monitored across a gradient of Cu conditions, characteristic of coastal and open-ocean surface waters. Cu deficiency had most severe effects on a Flavobacteriia member Dokdonia sp. strain Dokd-P16 for which we observed significant reductions in growth, C metabolism and Cu quotas. Other strains did not significantly reduce their growth rate, but adjusted their Cu content and some C metabolic rates (Ruegeria pomeroyi DSS-3, Roseobacter clade) or were unaffected (Pseudoalteromonas sp. strains PAlt-P26 and PAlt-P2, Alteromonadales clade). These diverse bacterial responses were accompanied by constant cellular composition of major elements and stoichiometric ratios. Changes in bacterial Cu quotas occurred within a modest range (∼5-fold range) relative to the 50-fold variation in total Cu in the media. We hypothesize that this may reflect a well-controlled Cu homeostasis in marine heterotrophic bacteria. In a preliminary assessment, we found that Cu quotas of bacteria and those of eukaryotic phytoplankton are not statistically different. However, compared to eukaryotic phytoplankton, the variability of Cu quotas in marine heterotrophic bacteria is smaller, which could reflect differences in their Cu homeostasis. Using Cu quotas obtained in our study, we assessed the contribution of bacterial Cu to the biogenic Cu pool in an oceanic euphotic zone in the NE Pacific. These preliminary estimates suggest that up to 50% of the biogenic Cu could be contained in the biomass of marine heterotrophic bacteria. Our study sheds light on the interactions between Cu and marine heterotrophic bacteria, demonstrating the potential for Cu to influence microbial ecology and for microbes to play role in Cu biolgeochemical cycle

Using 67Cu to Study the Biogeochemical Cycling of Copper in the Northeast Subarctic Pacific Ocean

Microbial copper (Cu) nutrition and dissolved Cu speciation were surveyed along Line P, a coastal to open ocean transect that extends from the coast of British Columbia, Canada, to the high-nutrient-low-chlorophyll (HNLC) zone of the northeast subarctic Pacific Ocean. Steady-state size fractionated Cu uptake rates and Cu:C assimilation ratios were determined at in situ Cu concentrations and speciation using a 67Cu tracer method. The cellular Cu:C ratios that we measured (~30 µmol Cu mol C-1) are similar to recent estimates using synchrotron x-ray fluorescence (SXRF), suggesting that the 67Cu method can determine in situ metabolic Cu demands. We examined how environmental changes along the Line P transect influenced Cu metabolism in the sub-microplankton community. Cellular Cu:C assimilation ratios and uptake rates were compared with net primary productivity, bacterial abundance and productivity, total dissolved Cu, Cu speciation, and a suite of other chemical and biological parameters. Total dissolved Cu concentrations ([Cu]d) were within a narrow range (1.46 to 2.79 nM), and Cu was bound to a ~5-fold excess of strong ligands with conditional stability constants ( ) of ~1014. Free Cu2+ concentrations were low (pCu 14.4 to 15.1), and total and size fractionated net primary productivity (NPPV; µg C L-1 d-1) were negatively correlated with inorganic Cu concentrations ([Cu′]). We suggest this is due to greater Cu′ drawdown by faster growing phytoplankton populations. Using the relationship between [Cu′] drawdown and NPPV, we calculated a regional photosynthetic Cu:C drawdown export ratio between 1.5 and 15 µmol Cu mol C-1, and a mixed layer residence time (2.5 to 8 years) that is similar to other independent estimates (2-12 years). Total particulate Cu uptake rates were between 22 and 125 times faster than estimates of Cu export; this is possibly mediated by rapid cellular Cu uptake and efflux by phytoplankton and bacteria or the effects of grazers and bacterial remineralization on dissolved Cu. These results provide a more detailed understanding of the interactions between Cu speciation and microorganisms in seawater, and present evidence that marine phytoplankton modify Cu speciation in the open ocean

Copper-binding ligands in the NE Pacific

WOS:000443668500004International audienceCopper distribution and speciation were determined at stations P4 and P26 along Line P as part of a GEOTRACES Process Study in the Northeast Pacific, at depths between 10 and 1400 m. Two ligand classes (L-1 and L-2) were detected at both stations: the stronger L-1 ligand pool with log K'(cu2+)(L1) 15.0-16.5 and the weaker L-2 ligand pool with log K'(cu2)(+L2) 11.6-13.6. The L-1 class bound on average 94% of dCu, with the ratio between L-1 and dCu constant and close to unity (1.15 = [L-1]:[dCu]). The concentrations of total ligands exceeded those of dCu at all depths, buffering Cu2+ concentrations ([Cu2+]) to femtomolar levels (i.e. pCu 14.1-15.7). Measurements using cathodic stripping voltammetry also identified natural copper-responsive peaks, which were attributed to thiourea- and glutathione-like thiols (TU and GSH, respectively), and Cu-binding humic substances (HScu). Concentrations of TU, GSH and HScu were determined by standard addition of model compounds in an attempt to identify Cu-binding ligands. HScu concentrations were generally higher at P26 than at P4, consistent with a marine origin of the humic material. Overall, HScu contributed to 1-27% of the total L concentration (L-T) and when combined with the two thiols contributed to up to 32% of L-T. This suggests other ligand types are responsible for the majority of dCu complexation in these waters, such as other thiols. Some potential candidates for detected, but unidentified, thiols are cysteine, 3-mercaptopropionic acid and 2-mercaptoethanol, all of which bind Cu. Significant correlation between the concentrations of TU-like thiols and L-1, along with the high log K'(cu)(2+)(L1) values, tentatively suggest that the electrochemical TU-type peak could be part of a larger, unidentified, high-affinity Cu compound, such as a methanobactin or porphyrin, with a stronger binding capability than typical thiols. This could imply that chalkophores may play a greater role in oceanic dCu complexation than previously considered