Posts Tagged 'growth'

The impact of elevated CO2 on Prochlorococcus and microbial interactions with ‘helper’ bacterium Alteromonas

Prochlorococcus is a globally important marine cyanobacterium that lacks the gene catalase and relies on ‘helper’ bacteria such as Alteromonas to remove reactive oxygen species. Increasing atmospheric CO2 decreases the need for carbon concentrating mechanisms and photorespiration in phytoplankton, potentially altering their metabolism and microbial interactions even when carbon is not limiting growth. Here, Prochlorococcus (VOL4, MIT9312) was co-cultured with Alteromonas (strain EZ55) under ambient (400p.p.m.) and elevated CO2 (800p.p.m.). Under elevated CO2, Prochlorococcus had a significantly longer lag phase and greater apparent die-offs after transfers suggesting an increase in oxidative stress. Whole-transcriptome analysis of Prochlorococcus revealed decreased expression of the carbon fixation operon, including carboxysome subunits, corresponding with significantly fewer carboxysome structures observed by electron microscopy. Prochlorococcus co-culture responsive gene 1 had significantly increased expression in elevated CO2, potentially indicating a shift in the microbial interaction. Transcriptome analysis of Alteromonas in co-culture with Prochlorococcus revealed decreased expression of the catalase gene, known to be critical in relieving oxidative stress in Prochlorococcus by removing hydrogen peroxide. The decrease in catalase gene expression was corroborated by a significant ~6-fold decrease in removal rates of hydrogen peroxide from co-cultures. These data suggest Prochlorococcus may be more vulnerable to oxidative stress under elevated CO2 in part from a decrease in ecosystem services provided by heterotrophs like Alteromonas. This work highlights the importance of considering microbial interactions in the context of a changing ocean.

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Effects of increased CO2 and temperature on the growth and photosynthesis in the marine macroalga Gracilaria lemaneiformis from the coastal waters of South China

The marine red macroalga Gracilaria lemaneiformis (Gracilariales, Rhodophyta) is one of the most important species for seaweed cultivation along the coastal waters of South China. In this study, G. lemaneiformis was incubated under present-day (390 ppm) or predicted-year CO2 levels (700 ppm), and under normal (20 °C) versus elevated temperatures (24 °C), to investigate possible effects of climate change conditions on the growth and photosynthesis. The chlorophyll a (Chl a), carotenoid (Car), and phycobiliprotein (PB) contents responded significantly to increased temperature under normal CO2 and high CO2 concentrations. However, CO2 enrichment in the culture had no significant impact on Chl a and Car but decreased the PB contents in G. lemaneiformis. The growth rates of G. lemaneiformis were significantly improved by increasing temperature, especially under concurrent increasing CO2 levels. Additionally, short-term exposure to high temperature stimulated the irradiance-saturated maximum photosynthetic rate (Pmax), and this stimulation was preserved with exposure to the high temperature in long-term incubations, with such stimulation being much more pronounced under normal CO2 concentrations than high CO2 concentrations. Results suggest that increased temperature exerted more pronounced effects on the growth and photosynthesis of G. lemaneiformis than increased CO2 concentrations did. We proposed that the sea cultivation of G. lemaneiformis would benefit from the ongoing climate change (increasing atmospheric CO2 concentrations and sea surface temperatures) through enhanced growth and carbon sequestration.

Continue reading ‘Effects of increased CO2 and temperature on the growth and photosynthesis in the marine macroalga Gracilaria lemaneiformis from the coastal waters of South China’

The effects of ocean acidification on growth, photosynthesis, and domoic acid production by the toxigenic diatom Pseudo-nitzschia australis

A northern California strain of Pseudo-nitzschia australis was examined using nonaxenic, batch cultures to examine the effects of more acidic conditions (reduced pH due to increased pCO2) on the growth, photosynthesis, and domoic acid production of this toxigenic diatom. Specific growth rates at the lowest pH tested (7.8) were 30 percent lower than the other three pH treatments (8.1, 8.0, 7.9). Macronutrient drawdown ratios of Si:N and Si:P decreased linearly with declining pH. Maximum rates of photosynthesis per cell were significantly elevated in the two lowest pH treatments relative to the control pH of 8.1. Domoic acid (DA) was detected in all pH treatments during both the nutrient-replete exponential growth phase and the nutrient-deplete stationary growth phase. Total cellular DA did not significantly differ among pH treatments during exponential growth, but increased with decreasing pH and reached a maximum of 3.61 pg DA • cell”1 during the stationary phase of growth.

Continue reading ‘The effects of ocean acidification on growth, photosynthesis, and domoic acid production by the toxigenic diatom Pseudo-nitzschia australis’

Changes in bioenergetics associated with ocean acidification and climate changes

Ocean global changes, including CO2-triggered ocean acidification and warming as well as associated changes in physical and chemical environments affect metabolisms of marine organisms and increase their energetic demand to cope with the environmental stresses. Phytoplankton species grown under ocean acidification conditions alter their metabolic pathways, down-regulating their CO2 concentrating mechanisms, up-regulating photorespiration and heatdissipating processes and generating extra energy by degrading accumulated phenolic compounds, which are toxic and can be transferred to higher trophic levels, changing food quality. Calcifying algae, under influence of ocean acidification, need more energy to maintain their calcification and to synthesize UV screening compounds due to reduced thickness of the calcified “shell”. Changes in the bioenergetics with exacerbating ocean global environmental issues will lead to ecological consequences and affect services of marine ecosystems.

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Effects of ocean acidification and UV radiation on marine photosynthetic carbon fixation

The oceans absorb anthropogenically released CO2 at a rate of more than one million tons per hour, which causes a pH decrease of seawater and results in ocean acidification (OA). The effect of OA and absorption of CO2 via the biological carbon pump driven by marine photosynthesis has drawn increasing attentions. As a consequence, there are numerous studies on influences of OA on primary producers, and the effects on photosynthetic carbon fixation are still under debate. OA can promote the growth of diatoms at low PAR irradiances and inhibit it at high PAR. Besides, OA may influence metabolic pathways of phytoplankton, upregulating β-oxidation, and the tricarboxylic acid cycle, resulting in increased accumulation of toxic phenolic compounds. In parallel, phytoplankton cells in the upper mixed layer are affected by intense PAR and UV radiation (UVR). The calcareous layers of calcified algae, which have been shown to shield the organisms from UVR, are thinned due to OA, exposing the cells to increased UVR and further inhibiting the calcification. Therefore, effects of OA and UV on marine photosynthetic carbon fixation could be compounded. While the photosynthetic carbon fixation is controlled by other environmental stressors in addition to OA and UV, such as nutrients limitation and warming, combined effects of OA and UV have been less considered. In this review, we synthesize and analyze recent advances on effects of OA and UV and their combined effects, implying that future studies should pay special attentions to ecological and physiological effects of OA in the presence of solar UV irradiance to reflect more realistic implications. The ecophysiological effects of OA and/or UV and their mechanisms in complex environments should be further explored.

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Coccolithophore growth and calcification in a changing ocean

Coccolithophores are the most abundant calcifying phytoplankton in the ocean. These tiny primary producers have an important role in the global carbon cycle, substantially contributing to global ocean calcification, ballasting organic matter to the deep sea, forming part of the marine food web base, and influencing ocean-atmosphere CO2 exchange. Despite these important impacts, coccolithophores are not explicitly simulated in most marine ecosystem models and, therefore, their impacts on carbon cycling are not represented in most Earth system models. Here, we compile field and laboratory data to synthesize overarching, across-species relationships between environmental conditions and coccolithophore growth rates and relative calcification (reported as a ratio of particulate inorganic carbon to particulate organic carbon in coccolithophore biomass, PIC/POC). We apply our relationships in a generalized coccolithophore model, estimating current surface ocean coccolithophore growth rates and relative calcification, and projecting how these may change over the 21st century using output from the Community Earth System Model large ensemble. We find that average increases in sea surface temperature of ∼2-3 °C leads to faster coccolithophore growth rates globally ( >10% increase) and increased calcification at high latitudes. Roughly an ubiquitous doubling of surface ocean pCO2 by the end of the century has the potential to moderately stimulate coccolithophore growth rates, but leads to reduced calcification ( ∼25% decrease). Decreasing nutrient availability (from warming-induced increases in stratification) produces increases in relative calcification, but leads to ∼25% slower growth rates. With all drivers combined, we observe decreases in calcification and growth in most low and mid latitude regions, with possible increases in both of these responses in most high latitude regions. Major limitations of our coccolithophore model stem from a lack of conclusive physiological responses to changes in irradiance (we do not include light limitation in our model), and a lack of physiological data for major coccolithophore species. Species within the Umbellosphaera genus, for example, are dominant in mid to low latitude regions where we predict some of the largest decreases in coccolithophore growth rate and calcification.

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Response to Comment on “The complex effects of ocean acidification on the prominent N2-fixing cyanobacterium Trichodesmium”

Hutchins et al. question the validity of our results showing that under fast growth conditions, the beneficial effect of high CO2 on Trichodesmium is overwhelmed by the deleterious effect of the concomitant decrease in ambient and cellular pH. The positive effect of acidification reported by Hutchins and co-workers is likely caused by culture conditions that support suboptimal growth rates.

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Ocean acidification in the IPCC AR5 WG II

OUP book