Blue-fluorescence of NADPH as an indicator of marine primary production

Nicotinamide Adenine Dinucleotide Phosphate (NADPH) is the primary product of photosynthesisand can therefore serve as an indicator of biomass and photosynthetic activity. Pure NADPH whichis the reduced form of NADP shows an absorption maximum at 340 nm and a maximum of emissionat 460 nm. NADPH concentrations in terrestrial vegetation have already been studied since1957 in great detail with optical methods. However, its potential as a biomass parameter of oceanicphytoplankton which can be assessed in situ and remotely with fluorescence spectroscopy has notyet been investigated.In this paper, we report on laboratory investigations of the blue-fluorescence spectrum in algalsuspensions of Chlorella and Thalassiosira when excited with UV-A light. It is shown that cell densitiesof about 106 per litre as they are typically found under natural conditions are too low for precisedetection of NADPH fluorescence, while concentrated samples with 108-1010 cells per litre exhibitsignificant blue-fluorescence which can be related to NADPH. Inhibition of photosynthetic activityby addition of DCMU decreases the strength of blue-fluorescence remarkably. Since NADPHis an end product of photosynthesis, changes of PAR illumination levels should directly affect itsconcentration and hence the intensity of blue-fluorescence. However, no effect of illumination onblue-fluorescence could be observed in our study. Possible reasons of these observations are discussed,and perspectives for practical applications of the method used are proposed

Coupling of heterotrophic bacteria to phytoplankton bloom development at different pCO₂ levels: a mesocosm study

The predicted rise in anthropogenic CO2 emissions will increase CO2 concentrations and decrease seawater pH in the upper ocean. Recent studies have revealed effects of pCO2 induced changes in seawater chemistry on a variety of marine life forms, in particular calcifying organisms. To test whether the predicted increase in pCO2 will directly or indirectly (via changes in phytoplankton dynamics) affect abundance, activities, and community composition of heterotrophic bacteria during phytoplankton bloom development, we have aerated mesocosms with CO2 to obtain triplicates with three different partial pressures of CO2 (pCO2): 350 μatm (1×CO2), 700 μatm (2×CO2) and 1050 μatm (3×CO2). The development of a phytoplankton bloom was initiated by the addition of nitrate and phosphate. In accordance to an elevated carbon to nitrogen drawdown at increasing pCO2, bacterial production (BPP) of free-living and attached bacteria as well as cell-specific BPP (csBPP) of attached bacteria were related to the C:N ratio of suspended matter. These relationships significantly differed among treatments. However, bacterial abundance and activities were not statistically different among treatments. Solely community structure of free-living bacteria changed with pCO2 whereas that of attached bacteria seemed to be independent of pCO2 but tightly coupled to phytoplankton bloom development. Our findings imply that changes in pCO2, although reflected by changes in community structure of free-living bacteria, do not directly affect bacterial activity. Furthermore, bacterial activity and dynamics of heterotrophic bacteria, especially of attached bacteria, were tightly correlated to phytoplankton development and, hence, may also potentially depend on changes in pCO2

Heterozygous, Polyploid, Giant Bacterium, Achromatium, Possesses an Identical Functional Inventory Worldwide across Drastically Different Ecosystems

Achromatium is large, hyperpolyploid and the only known heterozygous bacterium. Single cells contain approximately 300 different chromosomes with allelic diversity far exceeding that typically harbored by single bacteria genera. Surveying all publicly available sediment sequence archives, we show that Achromatium is common worldwide, spanning temperature, salinity, pH, and depth ranges normally resulting in bacterial speciation. Although saline and freshwater Achromatium spp. appear phylogenetically separated, the genus Achromatium contains a globally identical, complete functional inventory regardless of habitat. Achromatium spp. cells from differing ecosystems (e.g., from freshwater to saline) are, unexpectedly, equally functionally equipped but differ in gene expression patterns by transcribing only relevant genes. We suggest that environmental adaptation occurs by increasing the copy number of relevant genes across the cell’s hundreds of chromosomes, without losing irrelevant ones, thus maintaining the ability to survive in any ecosystem type. The functional versatility of Achromatium and its genomic features reveal alternative genetic and evolutionary mechanisms, expanding our understanding of the role and evolution of polyploidy in bacteria while challenging the bacterial species concept and drivers of bacterial speciation

Competition for inorganic and organic forms of nitrogen and phosphorous between phytoplankton and bacteria during an <i>Emiliania huxleyi</i> spring bloom

Using ¹⁵N and ³³P, we measured the turnover of organic and inorganic nitrogen (N) and phosphorus (P) substrates, and the partitioning of N and P from these sources into two size fractions of marine osmotrophs during the course of a phytoplankton bloom in a nutrient manipulated mesocosm. The larger size fraction (&gt;0.8 μm), mainly consisting of the coccolithophorid <i>Emiliania huxleyi</i>, but also including an increasing amount of large particle-associated bacteria as the bloom proceeded, dominated uptake of the inorganic forms NH₄⁺, NO₃^&minus;, and PO₄^3&minus;. The uptake of N from leucine, and P from ATP and dissolved DNA, was initially dominated by the 0.8&ndash;0.2 μm size fraction, but shifted towards dominance by the &gt;0.8 μm size fraction as the system turned to an increasing degree of N-deficiency. Normalizing uptake to biomass of phytoplankton and heterotrophic bacteria revealed that organisms in the 0.8&ndash;0.2 μm size fraction had higher specific affinity for leucine-N than those in the &gt;0.8 μm size fraction when N was deficient, whereas the opposite was the case for NH₄⁺. There was no such difference regarding the specific affinity for P substrates. Since heterotrophic bacteria seem to acquire N from organic compounds like leucine more efficiently than phytoplankton, our results suggest different structuring of the microbial food chain in N-limited relative to P-limited environments

Availability of phosphate for phytoplankton and bacteria and of labile organic carbon for bacteria at different pCO₂ levels in a mesocosm study

International audienceAvailability of phosphate for phytoplankton and bacteria and of labile organic carbon for bacteria at different pCO2 levels were studied in a mesocosm experiment (PeECE III). Using nutrient-depleted SW Norwegian fjord waters, three different levels of pCO2 (350 ?atm: 1×CO2; 750 ?atm: 2×CO2; 1050 ?atm: 3×CO2) were set up, and nitrate and phosphate were added at the start of the experiment in order to induce a phytoplankton bloom. Despite similar responses of total particulate P concentration and phosphate turnover time at the three different pCO2 levels, the size distribution of particulate P and 33PO4 uptake suggested that phosphate transferred to the >10 ?m fraction was greater in the 3×CO2 mesocosm during the first 6?10 days when phosphate concentration was high. During the period of phosphate depletion (after Day 12), specific phosphate affinity and specific alkaline phosphatase activity (APA) suggested a P-deficiency (i.e. suboptimal phosphate supply) but not a P-limitation for the phytoplankton and bacterial community at the three different pCO2 levels. Although specific phosphate affinity and specific APA tended to be higher in 3×CO2 than in 2×CO2 and 1×CO2 mesocosms during the phosphate depletion period, no statistical differences were found. Responses of specific glucose affinity for bacteria were similar at the three different pCO2 levels. Measured specific glucose affinities were consistently much lower than the theoretical maximum predicted from the diffusion-limited model, suggesting that bacterial growth was not limited by the availability of labile dissolved organic carbon. These results suggest that availability of phosphate and glucose was similar at the three different pCO2 levels

A feedback loop links brownification to anoxia in a temperate, shallow lake

This study examines a natural, rapid, fivefold increase in dissolved organic carbon (DOC) concentrations in a temperate shallow lake, describing the processes by which increased DOC resulted in anoxic conditions and altered existing carbon cycling pathways. High precipitation for two consecutive years led to rising water levels and the flooding of adjacent degraded peatlands. Leaching from the flooded soils provided an initial increase in DOC concentrations (from a 2010 mean of 12 ± 1 mg L−1 to a maximum concentration of 53 mg L−1 by June 2012). Increasing water levels, DOC, and phytoplankton concentrations reduced light reaching the sediment surface, eliminating most benthic primary production and promoting anoxia in the hypolimnion. From January to June 2012 there was a sudden increase in total phosphorus (from 57 µg L−1 to 216 µg L−1), DOC (from 24.6 mg L−1 to 53 mg L−1), and iron (from 0.12 mg L−1 to 1.07 mg L−1) concentrations, without any further large fluxes in water levels. We suggest that anoxic conditions at the sediment surface and flooded soils produced a dramatic release of these chemicals that exacerbated brownification and eutrophication, creating anoxic conditions that persisted roughly 6 months below a water depth of 1 m and extended periodically to the water surface. This brownification-anoxia feedback loop resulted in a near-complete loss of macroinvertebrate and fish populations, and increased surface carbon dioxide (CO2) emissions by an order of magnitude relative to previous years

Planktonic Aggregates as Hotspots for Heterotrophic Diazotrophy: The Plot Thickens

Biological dinitrogen (N-2) fixation is performed solely by specialized bacteria and archaea termed diazotrophs, introducing new reactive nitrogen into aquatic environments. Conventionally, phototrophic cyanobacteria are considered the major diazotrophs in aquatic environments. However, accumulating evidence indicates that diverse non-cyanobacterial diazotrophs (NCDs) inhabit a wide range of aquatic ecosystems, including temperate and polar latitudes, coastal environments and the deep ocean. NCDs are thus suspected to impact global nitrogen cycling decisively, yet their ecological and quantitative importance remain unknown. Here we review recent molecular and biogeochemical evidence demonstrating that pelagic NCDs inhabit and thrive especially on aggregates in diverse aquatic ecosystems. Aggregates are characterized by reduced-oxygen microzones, high C:N ratio (above Redfield) and high availability of labile carbon as compared to the ambient water. We argue that planktonic aggregates are important loci for energetically-expensive N-2 fixation by NCDs and propose a conceptual framework for aggregate-associated N-2 fixation. Future studies on aggregate-associated diazotrophy, using novel methodological approaches, are encouraged to address the ecological relevance of NCDs for nitrogen cycling in aquatic environments