Surface ocean microbiota determine cloud precursors

One pathway by which the oceans influence climate is via the emission of sea spray that may subsequently influence cloud properties. Sea spray emissions are known to be dependent on atmospheric and oceanic physicochemical parameters, but the potential role of ocean biology on sea spray fluxes remains poorly characterized. Here we show a consistent significant relationship between seawater nanophytoplankton cell abundances and sea-spray derived Cloud Condensation Nuclei (CCN) number fluxes, generated using water from three different oceanic regions. This sensitivity of CCN number fluxes to ocean biology is currently unaccounted for in climate models yet our measurements indicate that it influences fluxes by more than one order of magnitude over the range of phytoplankton investigated.

Detrimental effect of UV-B radiation on growth, photosynthetic pigments, metabolites and ultrastructure of some cyanobacteria and freshwater chlorophyta

BACKGROUND

Global warming directly influencing ozone layer depletion, which eventually is increasing ultraviolet radiation penetration having far-reaching impacts on living biota. This particularly influences the primary producer microalgae which are the basic unit of food webs in the aquatic habitats. Therefore, it is necessary to concentrate the research at this micro-level to understand the harmful impact of increased UV-B radiation ever before. Consequently, the present attempt aimed to focus on the influence of UV-B on growth criteria, photosynthetic pigments, some metabolites, and ultrastructure of the freshwater cyanobacteria, Planktothrix cryptovaginata (Microcoleaceae), Nostoc carneum (Nostocaceae), Microcystis aeruginosa (Microcystaceae), the Chlorophyte Scenedesmus acutus (Scenedesmaceae), and the marine Cyanobacterium Microcystis (Microcystaceae).

METHODS

The cultures of investigated algae were subjected directly to different duration periods (1, 3, 5, and 7 h) of artificial UV-B in addition to unirradiated control culture and allowed to grow for 10 days, after which the algal samples were analyzed for growth, photosynthetic activities, primary metabolities and cellular ultrastructure.

RESULTS

A remarkable inhibitory influence of UV-B was observed on growth criteria (measured as optical density and dry weight) and photosynthetic pigments of P. cryptovaginata, N. carneum, M. aeruginosa, S. acutus, and marine Microcystis. Where increasing the exposure time of UV-B was accompanied by increased inhibition. The variation in carbohydrate and protein contents under UV stress was based on the exposure periods and the algal species. The variation in algal ultrastructure by UV-B stress was noticed by an Electron Microscope. Cells damage and lysis, cell wall and cell membrane ruptured and release of intracellular substances, loss of cell inclusion, plasmolysis and necrosis, or apoptosis of the algal cells were observed by exposure to 7 h of UV-B.

CONCLUSION

Exposure to UV-B has a marked harmful impact on the growth, pigments, and metabolic activity, as well as the cellular ultrastructure of some cyanobacteria and chlorophytes.

Evolving paradigms in biological carbon cycling in the ocean

Carbon is a keystone element in global biogeochemical cycles. It plays a fundamental role in biotic and abiotic processes in the ocean, which intertwine to mediate the chemistry and redox status of carbon in the ocean and the atmosphere. The interactions between abiotic and biogenic carbon (e.g. CO2, CaCO3, organic matter) in the ocean are complex, and there is a half-century-old enigma about the existence of a huge reservoir of recalcitrant dissolved organic carbon (RDOC) that equates to the magnitude of the pool of atmospheric CO2. The concepts of the biological carbon pump (BCP) and the microbial loop (ML) shaped our understanding of the marine carbon cycle. The more recent concept of the microbial carbon pump (MCP), which is closely connected to those of the BCP and the ML, explicitly considers the significance of the ocean's RDOC reservoir and provides a mechanistic framework for the exploration of its formation and persistence. Understanding of the MCP has benefited from advanced ‘omics’ and novel research in biological oceanography and microbial biogeochemistry. The need to predict the ocean's response to climate change makes an integrative understanding of the BCP, ML and MCP a high priority. In this review, we summarize and discuss progress since the proposal of the MCP in 2010 and formulate research questions for the future.

SAR202 Genomes from the Dark Ocean Predict Pathways for the Oxidation of Recalcitrant Dissolved Organic Matter

Deep-ocean regions beyond the reach of sunlight contain an estimated 615 Pg of dissolved organic matter (DOM), much of which persists for thousands of years. It is thought that bacteria oxidize DOM until it is too dilute or refractory to support microbial activity. We analyzed five single-amplified genomes (SAGs) from the abundant SAR202 clade of dark-ocean bacterioplankton and found they encode multiple families of paralogous enzymes involved in carbon catabolism, including several families of oxidative enzymes that we hypothesize participate in the degradation of cyclic alkanes. The five partial genomes encoded 152 flavin mononucleotide/F420-dependent monooxygenases (FMNOs), many of which are predicted to be type II Baeyer-Villiger monooxygenases (BVMOs) that catalyze oxygen insertion into semilabile alicyclic alkanes. The large number of oxidative enzymes, as well as other families of enzymes that appear to play complementary roles in catabolic pathways, suggests that SAR202 might catalyze final steps in the biological oxidation of relatively recalcitrant organic compounds to refractory compounds that persist.IMPORTANCE Carbon in the ocean is massively sequestered in a complex mixture of biologically refractory molecules that accumulate as the chemical end member of biological oxidation and diagenetic change. However, few details are known about the biochemical machinery of carbon sequestration in the deep ocean. Reconstruction of the metabolism of a deep-ocean microbial clade, SAR202, led to postulation of new biochemical pathways that may be the penultimate stages of DOM oxidation to refractory forms that persist. These pathways are tied to a proliferation of oxidative enzymes. This research illuminates dark-ocean biochemistry that is broadly consequential for reconstructing the global carbon cycle.

The oligotrophic ocean is autotrophic

In vitro observations of net community production (NCP) imply that the oligotrophic subtropical gyres of the open ocean are net heterotrophic; in situ observations, in contrast, consistently imply that they are net autotrophic. At least one approach must be returning an incorrect answer. We find that (a) no bias in in situ oxygen-based production estimates would give false-positive (net autotrophy) rates, (b) observed (13)C enrichment of surface water dissolved inorganic carbon (DIC) can be explained only by positive NCP (net autotrophy), (c) lateral and vertical inputs of organic carbon are insufficient to sustain net heterotrophy, and (d) atmospheric input of organic material is too small to support in vitro rates of net heterotrophy and would yield δ(13)C depletion of surface DIC, quite the opposite of what is observed in the subtropical gyres. We conclude that the in vitro observations, implying net heterotrophy, must contain a bias that is due to an underestimate of photosynthetic rate and/or an overestimate of respiration rate.

Effects of solar UV-B radiation on aquatic ecosystems

Solar UV degrades dissolved organic carbon photolytically so that they can readily be taken up by bacterioplankton. On the other hand solar UV radiation inhibits bacterioplankton activity. Bacterioplankton productivity is far greater than previously thought and is comparable to phytoplankton primary productivity. According to the "microbial loop hypothesis," bacterioplankton is seen in the center of a food web, having a similar function to phytoplankton and protists. The penetration of UV and PAR into the water column can be measured. Marine waters show large temporal and regional differences in their concentrations of dissolved and particulate absorbing substances. A network of dosimeters (ELDONET) has been installed in Europe ranging from Abisko in Northern Sweden to Gran Canaria. Cyanobacteria are capable of fixing atmospheric nitrogen which is then made available to higher plants. The agricultural potential of cyanobacteria has been recognized as a biological fertilizer for wet soils such as in rice paddies. UV-B is known to impair processes such as growth, survival, pigmentation, motility, as well as the enzymes of nitrogen metabolism and CO2 fixation. The marine phytoplankton represents the single most important ecosystem on our planet and produces about the same biomass as all terrestrial ecosystems taken together. It is the base of the aquatic food chain and any changes in the size and composition of phytoplankton communities will directly affect food production for humans from marine sources. Another important role of marine phytoplankton is to serve as a sink for atmospheric carbon dioxide. Recent investigations have shown a large sensitivity of most phytoplankton organisms toward solar short-wavelength ultraviolet radiation (UV-B); even at ambient levels of UV-B radiation many organisms seem to be under UV stress. Because of their requirement for solar energy, the phytoplankton dwell in the top layers of the water column. In this near-surface position phytoplankton will be exposed to solar ultraviolet radiation. This radiation has been shown to affect growth, photosynthesis, nitrogen incorporation and enzyme activity. Other targets of solar UV irradiation are proteins and pigments involved in photosynthesis. Whether or not screening pigments can be induced in phytoplankton to effectively shield the organisms from excessive UV irradiation needs to be determined. Macroalgae show a distinct pattern of vertical distribution in their habitat. They have developed mechanisms to regulate their photosynthetic activity to adapt to the changing light regime and protect themselves from excessive radiation. A broad survey was carried out to understand photosynthesis in aquatic ecosystems and the different adaptation strategies to solar radiation of ecologically important species of green, red and brown algae from the North Sea, Baltic Sea, Mediterranean, Atlantic, polar and tropical oceans. Photoinhibition was quantified by oxygen exchange and by PAM (pulse amplitude modulated) fluorescence measurements based on transient changes of chlorophyll fluorescence.