Comprehensive fjord-systems represent major extensions of the coastline and are therefore important transfer zones of materials from land to ocean. Despite increased terrestrial inflows to fjords due to climate changes, we know little about the effects on the ecosystem, especially biogeochemical cycling. We present novel data on spatiotemporal variations of seston multielement stoichiometry in the Sognefjord, the second longest (204 km) and deepest (1308 m) fjord in the world, relative to environmental conditions and microbiota. Concentration of major elements was highest in the upper brackish layer whereas trace metals and minor elements were highest close to the bottom. Seasonally varying microbiota was an important part of the seston in surface waters. None of the seston C:N:P (molar) annual means at specific depths corresponded to the Redfield ratio (106:16:1). At 5 m, annual means of N/P and C/N were 8.4 and 6.5, respectively, while at depth (50–1220 m) N/P were on scale 3 times higher (21–31) and C/N 3 times lower (1.6–2.6), suggesting alternative N-sequestration mechanisms. Overall, correlations between C-Ca and C-S indicate a strong influence from calcite (CaCO3) and organosulfur producing microorganisms, while correlations between particulate Si and Mg–K–Ca–O at depth are consistent with clay and sinking diatom frustules. Mn concentrations increased strongly towards the bottom, likely from resuspension of MnO2 rich sediments and clay particles. Based on seston concentrations, we arrived at the following stoichiometric relationship: C55N16P1Si3.6Ca3.4O16Fe0.74Mn0.51Zn0.33S0.21Cu0.08Cl1.7Na0.68Mg0.71K0.37, although rarely measured, such information is a prerequisite for evaluating environmental impact on coastal ecosystems, biogeochemical cycling, pollution risk analysis and monitoring guidelines.

In food webs, interactions between competition and defence control the partitioning of limiting resources. As a result, simple models of these interactions contain links between biogeochemistry, diversity, food web structure and ecosystem function. Working at hierarchical levels, these mechanisms also produce self-similarity and therefore suggest how complexity can be generated from repeated application of simple underlying principles. Reviewing theoretical and experimental literature relevant to the marine photic zone, we argue that there is a wide spectrum of phenomena, including single cell activity of prokaryotes, microbial biodiversity at different levels of resolution, ecosystem functioning, regional biogeochemical features and evolution at different timescales; that all can be understood as variations over a common principle, summarised in what has been termed the 'Killing-the-Winner' (KtW) motif. Considering food webs as assemblages of such motifs may thus allow for a more integrated approach to aquatic microbial ecology.

The aim of this study was to reveal the relative content of C, N, Ca, Si, P, Mg, K, S and Fe in seston particles in Norwegian coastal water (NCW), and how it relates to biological and hydrographic processes during seasonal cycles from October 2009–March 2012. The following over all stoichiometric relationship for the time series was obtained: C66N11Si3.4Ca2.3P1Mg0.73S0.37K0.35Fe0.30, which is novel for marine waters. A record-breaking (187-year record) negative North Atlantic Oscillation (NAO) index caused extreme physical forcing on the Norwegian Coastal Current Water (NCCW) during the winter 2009–2010, and the inflow and upwelling of saline Atlantic water (AW) in the fjord was thus extraordinary during late spring-early summer in 2010. The element concentrations in fjord seston particles responded strongly to this convection, revealed by maximum values of all elements, except Fe, exceeding average values with 10.8× for Ca, 9.3 for K, 5.3 for S, 5.1 for Mg, 4.6 for Si, 4.0 for P, 3.8 for C, and 3.3 for N and Fe. This indicates that the signature of the Atlantic inflow was roughly two times stronger for Ca and K than for the others, probably connected with peaks in coccolithophorids and diatoms. There is, however, 1.5× more of Si than Ca contained in the seston, which could be due to a stronger dominance of diatoms than coccolithophorids, confirming their environmental fitness. In total our data do not indicate any severe nutrient limitation with respect to N, P and Fe, but accumulation of iron by Fe-sequestering bacteria might at times reduce the availability of the dissolved Fe-fraction. There is a high correlation between most of the measured elements, except for Ca, which together with Fe only weakly correlated with the other elements. It is to be expected that environmental alterations in NCW related to climate change will influence the seston elemental composition, but the full effect of this will be strongly dependent on the future dominance of the high pressure versus low pressure systems (i.e. NAO index), since they are key regulators for the direction of wind driven vertical convection (i.e. upwelling or downwelling). Changes in stratification, temperature, light, pH (ocean acidification), CaCO3 concentrations (carbon pump) and availability of nutrients in the euphotic zone (biogeochemical cycling) are essential for the future dominance of coccolithophorids versus diatoms.

Intracellular carbon (C), nitrogen (N) and phosphorus (P) content of marine phytoplankton and bacterioplankton can vary according to cell requirements or physiological acclimation to growth under nutrient limited conditions. Although such variation in macronutrient content is well known for cultured organisms, there is a dearth of data from natural populations that reside under a range of environmental conditions. Here, we compare C, N and P content of Synechococcus, Prochlorococcus, low nucleic acid (LNA) content bacterioplankton and small plastidic protists inhabiting surface waters of the North and South subtropical gyres and the Equatorial Region of the Atlantic Ocean. While intracellular C:N ratios ranged between 3.5 and 6, i.e. below the Redfield ratio of 6.6, all the C:P and N:P ratios were up to 10 times higher than the corresponding Redfield ratio of 106 and 16, respectively, reaching and in some cases exceeding maximum values reported in the literature. Similar C:P or N:P ratios in areas with different concentrations of inorganic phosphorus suggests that this is not just a response to the prevailing environmental conditions but an indication of the extremely low P content of these oceanic microbes.

This paper describes the development of a method for quantitative measurement of the elemental composition of particulate matter (PM) in seawater. This method is based on use of wavelength dispersive X-ray fluorescence (WDXRF) analysing PM harvested on various filter types. As the amount of material is less than a monolayer of cells on the filters we reduced the need for absorption correction. Given the appropriate combination of filters and elements the detection limits are low: <1 µg/filter for carbon (C), nitrogen (N), and <0.1 µg/filter for silicon (Si), phosphorus (P), calcium (Ca) and iron (Fe). The analytical range used was90–750 µgC,23–116 µgN and7–30 µgP, depending on the filters applied. Calibration constants for the elements included in this study were obtained from analysis of known quantities of chemical compounds on filters or silver plates. For carbon and nitrogen we also used comparative measurements ofSynechococcussp. cultures by CHN analyser and WDXRF. We harvested PM from 150 ml to 2000 ml on each filter in three replicates, obtaining less than 5% analytical variability between the replicates. One of the challenges using WDXRF as proposed here is the absorption of X-ray signals by the filter and variability of cell/particle sizes, and, consequentlyly, the variability of harvested PM on various filters. We find that an anodisc filter is best suited for C and N, while polycarbonate filters are best for heavier elements. Here we present analytical details and some data from field experiments related to C, N, P, Si, Ca and Fe in particles from seawater.

Biogenic production and sedimentation of calcium carbonate in the ocean, referred to as the carbonate pump, has profound implications for the ocean carbon cycle, and relate both to global climate, ocean acidification and the geological past. In marine pelagic environments coccolithophores, foraminifera and pteropods have been considered the main calcifying organisms. Here, we document the presence of an abundant, previously unaccounted fraction of marine calcium carbonate particles in seawater, presumably formed by bacteria or in relation to extracellular polymeric substances. The particles occur in a variety of different morphologies, in a size range from <1 to >100 µm, and in a typical concentration of 104–105 particles L−1 (size range counted 1–100 µm). Quantitative estimates of annual averages suggests that the pure calcium particles we counted in the 1–100 µm size range account for 2–4 times more CaCO3 than the dominating coccolithophoride Emiliania huxleyi and for 21% of the total concentration of particulate calcium. Due to their high density, we hypothesize that the particles sediment rapidly, and therefore contribute significantly to the export of carbon and alkalinity from surface waters. The biological and environmental factors affecting the formation of these particles and possible impact of this process on global atmospheric CO2 remains to be investigated.

Quantitative characterization of the mode and rate of phenotypic evolution is rarely applied to prokaryotes. Here, we present an analysis of temperature optimum (T (opt)) evolution in the thermophilic family Thermotogaceae, which has a large number of cultured representatives. We use log-rate-interval analysis to show that T (opt) evolution in Thermotogaceae is consistent with a Brownian motion (BM) evolutionary model. The properties of the BM model are used to a establish confidence intervals on the unknown phenotypic trait value of an uncultured organism, given its distance to a close relative with known trait value. Cross-validation by bootstrapping indicates that the predictions are robust.

Vibrio natriegens cultivated in a phosphate-limited chemostat at dilution rates of 0.32, 0.20, and 0.13 h−1 was given pulses of phosphate in an otherwise complete medium. Under the conditions used, complete depletion of phosphate occurred within 2–3 h and was followed by uptake of glucose and by cell division. For the most severely phosphate-limited cells (cultivated in the chemostat at dilution rate of 0.13 h−1), the elemental composition was determined by X-ray analysis at different times after adding phosphate. The amount of phosphorus per cell increased rapidly after the phosphate pulse but decreased when the cells started to divide after 2 h. An initial increase followed by a decrease was also found for chlorine, while the amount of sulphur remained constant before decreasing. Chlorine and calcium showed more complicated patterns. The pattern for magnesium, with a maximum after 45 min, may indicate a correlation between magnesium content and cell division. Multivariate analysis showed that cells differed significantly between sampling times. Addition of phosphate to the phosphate-starved culture also induced synthesis of polyphosphate bodies in the cells. Within 15 min an average of 3.8% of the cell volume consisted of polyphosphate bodies as shown by transmission electron microscopy. These bodies disappeared after an additional 30–60 min, indicating that polyphosphate is synthesized to facilitate phosphate uptake by minimizing the concentration gradient across the cell membrane.

Cells maintain an osmotic pressure essential for growth and division, using organic compatible solutes and inorganic ions. Mg2+, which is the most abundant divalent cation in living cells, has not been considered an osmotically important solute. Here we show that under carbon limitation or dormancy native marine bacterial communities have a high cellular concentration of Mg2+ (370–940 mm) and a low cellular concentration of Na+ (50–170 mm). With input of organic carbon, the average cellular concentration of Mg2+ decreased 6–12-fold, whereas that of Na+ increased ca 3–4-fold. The concentration of chlorine, which was in the range of 330–1200 mm, and was the only inorganic counterion of quantitative significance, balanced and followed changes in the concentration of Mg2++Na+. In an osmotically stable environment, like seawater, any major shift in bacterial osmolyte composition should be related to shifts in growth conditions, and replacing organic compatible solutes with inorganic solutes is presumably a favorable strategy when growing in carbon-limited condition. A high concentration of Mg2+ in cells may also serve to protect and stabilize macromolecules during periods of non-growth and dormancy. Our results suggest that Mg2+ has a major role as osmolyte in marine bacteria, and that the [Mg2+]/[Na+] ratio is related to its physiological condition and nutritional status. Bacterial degradation is a main sink for dissolved organic carbon in the ocean, and understanding the mechanisms limiting bacterial activity is therefore essential for understanding the oceanic C-cycle. The [Mg2+]/[Na+]-ratio in cells may provide a physiological proxy for the transitions between C-limited and mineral nutrient-limited bacterial growth in the ocean's surface layer.

We examined morphology, elemental composition (C, N, P), and orthophosphate-uptake efficiency in the marine heterotrophic bacterium Vibrio splendidus grown in continuous cultures. Eight chemostats were arranged along a gradient of increasing glucose concentrations in the reservoirs, shifting the limiting factor from glucose to phosphate. The content of carbon, nitrogen, and phosphorus was measured in individual cells by x-ray microanalysis using a transmission electron microscope (TEM). Cell volumes (V) were estimated from length and width measurements of unfixed, air-dried cells in TEM. There was a transition from coccoid cells in C-limited cultures toward rod-shaped cells in P-limited cultures. Cells in P-limited cultures with free glucose in the media were significantly larger than cells in glucose-depleted cultures (P < 0.0001). We found functional allometry between cellular C-, N-, and P content (in femtograms) and V (in cubic micrometers) in V. splendidus (C = 224 × V 0.89, N = 52.5 × V 0.80, P = 2 × V 0.65); i.e., larger bacteria had less elemental C, N, and P per V than smaller cells, and also less P relative to C. Biomass-specific affinity for orthophosphate uptake in large P-limited V. splendidus approached theoretical maxima predicted for uptake limited by molecular diffusion toward the cells. Comparing these theoretical values to respective values for the smaller, coccoid, C-limited V. splendidus indicated, contrary to the traditional view, that large size did not represent a trade-off when competing for the non-C-limiting nutrients.

Feeding the oceans: more carbon is less An experiment in which degradable organic carbon was added to Arctic waters has come up with the counterintuitive finding that in certain conditions, the addition of carbon actually reduces total organic carbon in the ecosystem. The outcome depends on the species interactions within the food web and how they are affected by nutrient supply. When mineral nutrients are limiting, organic carbon accumulates in the system, while in a system limited by organic carbon, marine bacteria are able to outcompete phytoplankton, with the net result a reduction in total organic carbon. This result highlight how descriptions of present and future states of the oceanic carbon cycle depend upon an understanding of the stoichiometric coupling between carbon and growth-limiting mineral nutrients within the marine food web.

Mesocosm experiments are important for studies of the pelagic ecosystem, and reproducibility of population dynamics and the effect of enclosing the water mass are essential aspects of such experiments. Nine mesocosms manipulated with daily nutrient additions were divided into three treatment groups, each of three units. All units were filled on the same day, but the three treatment groups differed in the timing of the start of nutrient additions. Abundance of phytoplankton, viruses and bacteria was followed for 12 days after filling, and 80% of the variance was ascribed to the population dynamics initiated by the nutrient perturbation, only 3% to the difference in the starting time of the perturbation and 1% to the placement of individual mesocosms at the raft. Although within-group variance of nutrient perturbation was small, there was a continuous increase over time, demonstrating a tendency for mesocosms to slowly diverge. We conclude that the transient response induced by the experimental perturbation strongly dominates the observed abundance variations and that, although present, the effects of delaying the onset of nutrient perturbation and of differences in along-raft position of the mesocosms were comparatively much smaller. Consequences for design of numerical models of microbial population dynamics are discussed.

We measured the elemental composition of single cells from six strains of marine Prochlorococcus and two strains of marine Synechococcus by X‐ray microanalysis in the transmission electron microscope (TEM), which allows measurements of all major elements in cells without any fixation or staining. The mean carbon : volume ratios ranged from 136 to 280 fg µm −3 in Prochlorococcus and 138 to 290 fg µm −3 in Synechococcus . Using mean values of elemental content of C:N:O: P : S, we obtained molar ratios of 143–214 : 15–24 : 15–41 : 1 : 0.58–1.64, and 65–293 : 7–36 : 11–36 : 1 : 0.31–1.54 for strains of Prochlorococcus and Synechococcus, respectively. The diffusible ions Mg++ (89–490 mmol L −1 ) and Na+ (230–660 mmol L −1 ) dominated in Prochlorococcus . In Synechococcus Na+ (90–480 mmol L −1 ) dominated. For all samples the range of K+ content was 23–130 mmol L −1 . Elemental composition varied widely in relation to strains and growth media. However, C: P and N: P ratios were above the Redfield ratio in all Prochlorococcus strains and one of the Synechococcus strains (WH 8103). This likely reflected the low P content of these cells. This low P requirement would be clearly advantageous in the oligotrophic conditions occupied by these organisms. The high relative carbon content, compared to what has been found for heterotrophic bacteria using similar methods, is suggested to confer a competitive advantage to photosynthetic over heterotrophic bacteria in ecosystems where both functional groups are mineral nutrient limited.

Accurate assessments of the true elemental cellular content of carbon (C), nitrogen (N), and phosphorus (P) in bacteria have been a major difficulty in microbial research for some time. This study is the first to present single‐cell elemental C, N, and P measurements on natural populations of bacteria from the Sargasso Sea using a transmission electron microscope (TEM) equipped with an X‐ray detector unit. Elemental cell content showed a best fit as a power function of the cell size, and smaller bacteria had significantly more elemental C, N, and P per cell volume than the larger ones (scaling factor a < 1). Contrary to coastal, brackish, and freshwater systems, the bacteria collected in this study appeared to have a molar elemental P :N close to the Redfield ratio of 0.063 (N:P = 16). The geometric mean of C per cell volume analyzed in this study (148 fg C µm−3) was higher than any other estimates reported from coastal and brackish water systems. Total amount of bacterial C calculated from abundance estimates requires an average conversion factor, and the choice of a representative bacterial cell volume is therefore critical. We were able to demonstrate that the outcome of biomass assessments is highly dependant on the choice of cell‐specific conversion factors. By applying cell volumes previously reported from the BATS site, the average 0–250 m depth integration of bacterial C between 1991 and 1996 ranged between 1.7 and 2.5 times less than other recent biomass estimates for these waters.

Marine bacterioplankton were isolated and grown in batch cultures until their growth became limited by organic carbon (C), nitrogen (N), or phosphorus (P). Samples were taken from the cultures at both the exponential and stationary phases. The elemental composition of individual bacterial cells was analyzed by X-ray microanalysis with an electron microscope. The cell size was also measured. The elemental content was highest in exponentially growing cells (149 +/- 8 fg of C cell(-1), 35 +/- 2 fg of N cell(-1), and 12 +/- 1 fg of P cell(-1); average of all isolates +/- standard error). The lowest C content was found in C-limited cells (39 +/- 3 fg of C cell(-1)), the lowest N content in C- and P-limited cells (12 +/- 1 and 12 +/- 2 fg of N cell(-1), respectively), and the lowest P content in P-limited cells (2.3 +/- 0.6 fg of P cell(-1)). The atomic C:N ratios varied among treatments between 3.8 +/- 0.1 and 9.5 +/- 1.0 (average +/- standard error), the C:P ratios between 35 +/- 2 and 178 +/- 28, and the N:P ratios between 6.7 +/- 0.3 and 18 +/- 3. The carbon-volume ratios showed large variation among isolates due to different types of nutrient limitation (from 51+/- 4 to 241 +/- 38 fg of C microm(-1); average of individual isolates and treatments +/- standard error). The results show that different growth conditions and differences in the bacterial community may explain some of the variability of previously reported elemental and carbon-volume ratios.

Salinibacter ruber is a red obligatory aerobic chemoorganotrophic extremely halophilic Bacterium, related to the order Cytophagales. It was isolated from saltern crystallizer ponds, and requires at least 150 g l–1 salt for growth. The cells have an extremely high potassium content, the ratio K+/protein being in the same range as in halophilic Archaea of the order Halobacteriales. X-ray microanalysis in the electron microscope of cells grown in medium of 250 g l–1 salt confirmed the high intracellular K+ concentrations, and showed intracellular chloride to be about as high as the cation concentrations within the cells. A search for intracellular organic osmotic solutes, using 13C-NMR and HPLC techniques, showed glutamate, glycine betaine, and N-α-acetyllysine to be present in low concentrations only, contributing very little to the overall osmotic balance. The results presented suggest that the extremely halophilic Bacterium Salinibacter uses a similar mode of haloadaptation to that of the Archaea of the order Halobacteriales, and does not accumulate organic osmotic solutes such as are used by all other known halophilic and halotolerant aerobic Bacteria.

In this study we have quantified the ionic content and volume of native aquatic, and two cultured bacteria, by X-ray microanalysis (XRMA) in the transmission electron microscope (TEM). The cellular concentrations of magnesium (means of 630 and 710 mM) were more than an order of a magnitude higher than the outside concentrations. The internal concentrations of sodium were on average 50-180 mM, and the [K+]/[Na+] ratios were in the range of 0.1-0.5; lowest for apparently nonactive bacteria. Magnesium and chloride probably act as the major components of cell turgor, since no other inorganic ions were present in comparable amounts. Our carbon and nitrogen measurements indicated that organic solutes are not likely to be present at significant concentrations. The estimated charge of inorganic ions (Na, Mg, P, Cl, K, and Ca) gave a positive net internal charge for most cells. However, in cultures of Vibrio natriegens, the high internal chloride concentration made the net inorganic charge negative in these cells. Our results suggest that growing marine bacterioplankton have an internal environment in which magnesium is the dominating cation. These results suggest that actively growing marine bacteria are physiologically adapted to high internal concentrations of both magnesium and chloride.