Jason R. Graff

A common partitioning strategy for photosynthetic products in evolutionarily distinct phytoplankton species

· We compare the nutrient-dependent photosynthetic efficiencies of the chlorophyte, Dunaliella tertiolecta, with those of the marine diatom, Thalassiosira weissflogii. Despite considerable evolutionary and physiological differences, these two species appear to use nearly identical growth strategies under a wide range of nutrient limitation. · Using a variety of physiological measurements, we find that, for both species and across all growth rates, 75% of the gross photosynthetic electron flow is invested in carbon fixation and only 30% is retained as net carbon accumulation. A majority of gross photosynthesis (70%) is ultimately used as reductant for biosynthetic pathways and for the generation of ATP. · In both species, newly formed carbon products exhibit much shorter half-lives at slow growth rates than at fast growth rates. We show that this growth rate dependence is a result of increased polysaccharide storage during the S phase of the cell cycle. · We present a model of carbon utilization that incorporates this growth rate-dependent carbon allocation and accurately captures (r(2) = 0.94) the observed time-resolved carbon retention. Together, our findings suggest a common photosynthetic optimization strategy in evolutionarily distinct phytoplankton species and contribute towards a systems-level understanding of carbon flow in photoautotrophs.

Vibrio cholerae exploits sub-lethal concentrations of a competitor-produced antibiotic to avoid toxic interactions

Vibrio cholerae is a human pathogenic marine bacterium inhabiting coastal regions and is vectored into human food and water supplies via attachment to particles including detritus, phytoplankton, and zooplankton. Particle colonization by the pathogen is inhibited by an antagonistic interaction with the particle-associated Vibrionales bacterium SWAT3, a producer of the antibiotic andrimid. By analyzing the individual movement behaviors of V. cholerae exposed to a gradient of andrimid in a microfluidics device, we show that the pathogen has a concentration dependent avoidance response to sub-lethal concentrations of the pure antibiotic and to the metabolites produced by a growing colony of SWAT3-wild-type. This avoidance behavior includes a 25% increase in swimming speeds, 30% increase in run lengths, and a shift in the direction of the bacteria away from the andrimid source. Consequently, these behavioral shifts at low concentrations of andrimid would lead to higher diffusivity and result in the dispersion of bacteria away from the competitor and source of the antibiotic. Such alterations in motility were not elicited in response to a non-andrimid-producing SWAT3 mutant, suggesting andrimid may be a negative effector of chemotaxis for V. cholerae. The behavioral response of colonizing bacteria to sub-inhibitory concentrations of competitor-produced antibiotics is one mechanism that can influence microbial diversity and interspecific competition on particles, potentially affecting human health in coastal communities and element cycling in the ocean.

A new species of Malacoceros (Polychaeta: Spionidae) from Kick'em Jenny, a hydrothermally active submarine volcano in the Lesser Antilles Arc

A new spionid polychaete, Malacoceros jennicus, is described from the crater of a hydrothermally active submarine volcano near Grenada in the Caribbean, Lesser Antilles Arc region. The new species is characterized by having prominent lateral frontal horns on the prostomium, paired eye spots, neurosetae that include simple capillaries, inferior sabre setae, numerous bidentate hooded hooks, and a pygidium bearing four digitiform anal cirri surrounding the anus. Worms were collected in regions of diffuse venting with a suction sampler deployed on an ROV. Specimens representing a range of sizes including sexually mature and reproductive individuals containing eggs and sperm were found. Stable isotope analysis of 13 C and 15 N indicate mixed feeding on photosynthetic and hydrothermal vent source material.

Photoacclimation Responses in Subarctic Atlantic Phytoplankton Following a Natural Mixing-Restratification Event

Strong physical disturbances in the surface ocean vertically redistribute plankton and lead to new relationships between organisms and their growth environment. Entrainment of phytoplankton to deeper depths decreases light exposure while stratification exposes cells in the surface mixing layer to higher light. Phytoplankton can rapidly respond to alterations in growth irradiance using photoacclimation processes such as nonphotochemical quenching and alterations in pigments and other macromolecules. While it is common to observe photophysiological responses to shifts in growth irradiance in the laboratory it is rare that a study is able to document these processes in the field in a lagrangian framework. We were able to follow a natural phytoplankton community for four days and observe rapid photophysiological responses and net accumulation patterns of biomass down to 200 m following a deep mixing and restratification event in the subarctic Atlantic ocean. Applying flow cytometry and fast rate repetition fluorometry (FRRf) we report on the photoacclimation responses of multiple taxonomic groups in relation to the rapidly evolving physical environment. Significant stratification occurred following the deep entrainment event, isolating cells within an actively mixing and shoaling surface layer, the lower euphotic zone, and below the photic zone. Distinct differences in patterns of accumulation and photoacclimation are apparent between these depths of disparate light histories. Photoacclimation patterns are generally consistent between Synechococcus, picoeukaryote, and nanoeukaryote groups yet diel patterns and variability in the range of photoacclimation suggest divergent physiology. Results from continuous FRRf measurements collected on bulk seawater show a decrease in the number photosystem II reaction centers and a concurrent increase in the functional cross section with implications for maintaining photosynthetic rates throughout the mixed layer. Understanding group specific differences as well as bulk community acclimation strategies will be important for informing models relying on photoacclimation parameters to determine growth and accumulation rates and net primary production. More so, the rates at which cells acclimate within the context of the frequency and spatial dynamics of storm events, such as the one recorded here, directly impact interpretations and applications of remote retrievals of phytoplankton chlorophyll, carbon, and their ratio in the context of unbalanced growth.

Intercomparison of Ocean Color Algorithms for Picophytoplankton Carbon in the Ocean

The differences among phytoplankton carbon (

Evaluating Optical Proxies of Particulate Organic Carbon across the Surface Atlantic Ocean

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Revaluating ocean warming impacts on global phytoplankton

) predictions from six ocean colour algorithms are investigated by comparison with \textit{in situ} estimates of phytoplankton carbon. The common satellite data used as input for the algorithms is the Ocean Colour Climate Change Initiative merged product. The matching \textit{in situ} data are derived from flow cytometric cell counts and per-cell carbon estimates for different types of pico-phytoplankton. This combination of satellite and \textit{in situ} data provides a relatively large matching dataset (N

Analytical phytoplankton carbon measurements spanning diverse ecosystems

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The measurement of phytoplankton biomass using flow-cytometric sorting and elemental analysis of carbon

500), which is independent from most of the algorithms tested and spans almost two orders of magnitude in

Extraction method influences the recovery of phytoplankton pigments from natural assemblages

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