אם אין שם משתמש, נא להיכנס בעזרת מספר תעודת זהות או מספר דרכון
Margarita Zarubin, Shimshon Belkin, Michael Ionescu and Amatzia Genin
The benefits of bioluminescence for nonsymbiotic marine bacteria have not been elucidated fully. One of the most commonly cited explanations, proposed more than 30 y ago, is that bioluminescence augments the propagation and dispersal of bacteria by attracting fish to consume the luminous material. This hypothesis, based mostly on the prevalence of luminous bacteria in fish guts, has not been tested experimentally. Here we show that zooplankton that contacts and feeds on the luminescent bacterium Photobacterium leiognathi starts to glow, and demonstrate by video recordings that glowing individuals are highly vulnerable to predation by nocturnal fish. Glowing bacteria thereby are transferred to the nutritious guts of fish and zooplankton, where they survive digestion and gain effective means for growth and dispersal. Using bioluminescence as bait appears to be highly beneficial for marine bacteria, especially in food-deprived environments of the deep sea.
Rubin, M., Berman-Frank, I. & Y. Shaked.
Nature Geoscience: 2011; 4(529-534)
Trichodesmium, a filamentous dinitrogen-fixing cyanobacterium, forms extensive blooms in nutrient-poor tropical and subtropical ocean waters. These cyano-bacteria contribute significantly to biological fixation of nitrogen from the atmosphere in these waters, and thereby fuel primary production and influence nutrient flow and the cycling of organic and inorganic matter. Trichodesmium blooms require large quantities of iron, which is partly supplied by the influx of wind-blown dust. However, the processes and mechanisms associated with dust acquisition are poorly understood. Here, we incubate natural populations and laboratory cultures of Trichodesmium with isotopically labelled iron oxides and desert dust, to determine how these cyanobacteria collect, process and use particulate iron. We show that, like most phytoplankton, Trichodesmium acquires only dissolved iron. However, unlike other studied phytoplankton, Trichodesmium accelerates the rate of iron dissolution from oxides and dust, through as yet unspecified cell-surface processes, and thereby increases cellular iron uptake rates. We show that natural puff (ball-shaped) colonies of Trichodesmium are particularly effective at dissolving dust and oxides, which we attribute to efficient dust trapping in their intricate colony morphology, followed by active shuttling and packaging of the dust within the colony core. We suggest that colony formation in Trichodesmium is an adaptive strategy that enhances iron acquisition from particulate sources such as dust.
Yoni Sharon, Orly Levitan, Dina Spungin, Ilana Berman-Frank and Sven Beer
Limnol. Oceanogr. 2011: 56 (357-362)
The seagrass Halophila stipulacea grows in the northern Red Sea from the intertidal to depths of ~ 50 m. Along that gradient, there is a > 1 order of magnitude difference in irradiance and the spectrum narrows from that of full sunlight to dim blue-green light. Based on these differences, we set out to estimate the molar ratios and potential contributions of photosystem II (PSII) and photosystem I (PSI) to light absorption, and photosynthetic electron transport rates (ETR), in plants growing at 1-m and 48-m depths. The amount of PsaC (a proxy for PSI) was three times higher in the deep-growing plants. On the other hand, the amount of PsbA (a proxy for PSII) did not differ significantly between the two depths. Thus, the PSII : (PSII + PSI) ratio (FII) was 0.62 in the shallow and 0.41 in the deep-growing plants. Similar results were obtained by 77K emission fluorescence. Because ETR is linearly dependent on FII, it follows that the ETR vs. irradiance curves differed significantly if calculated based on the commonly used FII value of 0.5 or the FII values we found. As a result, the photosynthetic parameters ETRmax and α also differed when using the different FII values. Correct(ed) FII values should, therefore, be used in the calculation of photosynthetic ETRs. The ability of H. stipulacea to alter its amount of PSI relative to PSII according to the ambient irradiance and spectrum may be one reason why this organism can grow down to its exceptional depth limit in clear tropical waters.
Meron D., Atias E., Kruh L.I., Elifantz H., Minz D., Fine M. & E. Banin.
The ISME Journal; 2011; 5(51-60)
Rising concentrations of atmospheric carbon dioxide are acidifying the world's oceans. Surface seawater pH is 0.1 units lower than pre-industrial values and is predicted to decrease by up to 0.4 units by the end of the century. This change in pH may result in changes in the physiology of ocean organisms, in particular, organisms that build their skeletons/shells from calcium carbonate, such as corals. This physiological change may also affect other members of the coral holobiont, for example, the microbial communities associated with the coral, which in turn may affect the coral physiology and health. In the present study, we examined changes in bacterial communities in the coral mucus, tissue and skeleton following exposure of the coral Acropora eurystoma to two different pH conditions: 7.3 and 8.2 (ambient seawater). The microbial community was different at the two pH values, as determined by denaturing gradient gel electrophoresis and 16S rRNA gene sequence analysis. Further analysis of the community in the corals maintained at the lower pH revealed an increase in bacteria associated with diseased and stressed corals, such as Vibrionaceae and Alteromonadaceae. In addition, an increase in the number of potential antibacterial activity was recorded among the bacteria isolated from the coral maintained at pH 7.3. Taken together, our findings highlight the impact that changes in the pH may have on the coral-associated bacterial community and their potential contribution to the coral host.
Mass T., Genin A., Shavit U., Grinstein M. & D. Tchernov
PNAS: 2010: 107(2527-2531)
Worldwide, many marine coastal habitats are facing rapid deterioration due in part to human-driven changes in habitat characteristics, including changes in flow patterns, a factor known to greatly affect primary production in corals, algae, and seagrasses. The effect of flow traditionally is attributed to enhanced influx of nutrients and dissolved inorganic carbon (DIC) across the benthic boundary layer from the water to the organism however, here we report that the organism’s photosynthetic response to changes in the flow is nearly instantaneous, and that neither nutrients nor DIC limits this rapid response. Using microelectrodes, dual-pulse amplitude-modulated fluorometry, particle image velocimetry, and real time mass-spectrometry with the common scleractinian coral Favia veroni, the alga Gracilaria cornea, and the seagrass Halophila stipulacea, we show that this augmented photosynthesis is due to flow-driven enhancement of oxygen efflux from the organism to the water, which increases the affinity of the RuBisCO to CO2. No augmentation of photosynthesis was found in the absence of flow or when flow occurred, but the ambient concentration of oxygen was artificially elevated. We suggest that water motion should be considered a fundamental factor, equivalent to light and nutrients, in determining photosynthesis rates in marine benthic autotrophs.
Tali Mass & Amatzia Genin
Mar. Ecol. Prog. Ser.
The morphology of corals is strongly dependent on environmental conditions. Different morphologies can be induced by flow and light due to their effects on respiration, production, calcification and prey capture. Yet, colonies of many branching corals exhibit a radial symmetry, possibly indicating an intrinsic determination of colony morphology. The scleractinian coral Pocillopora verrucosa (Ellis and Solander, 1786) is a common species in the Red Sea, displaying striking flow-dependent plasticity in colony morphology. Branches of this coral are thicker and more compact in habitats exposed to stronger flow, but the colonies are usually radially symmetric. The objective of this study was to experimentally examine whether the colony symmetry in this species is determined by intrinsic or extrinsic factors.
Six corals were exposed in situ for 4 mo to a unidirectional flow generated with submerged pumps, creating asymmetric flow, stronger at the side facing the pump. The up-current side of the corals developed higher concentrations of chlorophyll and proteins, greater density of zooxanthellae, and displayed a more compact morphology and longer linear extension. While asymmetry in photosynthesis and photosynthates may disappear due to within-colony translocation, our findings on asymmetry in skeletal growth and morphology indicate that environmental conditions generate lasting asymmetry in corals. Current measurements indicate that the ubiquitous symmetry observed in P. verrucosa is apparently due to a corresponding symmetry in the flow.