Dataset Information

Inorganic carbon and pH dependency of photosynthetic rates in Trichodesmium.

ABSTRACT: Increasing atmospheric CO2 concentrations are leading to increases in dissolved CO2 and HCO3- concentrations and decreases in pH and CO32- in the world's oceans. There remain many uncertainties as to the magnitude of biological responses of key organisms to these chemical changes. In this study, we established the relationship between photosynthetic carbon fixation rates and pH, CO2, and HCO3- concentrations in the diazotroph, Trichodesmium erythraeum IMS101. Inorganic 14C-assimilation was measured in TRIS-buffered artificial seawater medium where the absolute and relative concentrations of CO2, pH, and HCO3- were manipulated. First, we varied the total dissolved inorganic carbon concentration (TIC) (<0 to ~5 mM) at constant pH, so that ratios of CO2 and HCO3- remained relatively constant. Second, we varied pH (~8.54 to 7.52) at constant TIC, so that CO2 increased whilst HCO3- declined. We found that 14C-assimilation could be described by the same function of CO2 for both approaches, but it showed different dependencies on HCO3- when pH was varied at constant TIC than when TIC was varied at constant pH. A numerical model of the carbon-concentrating mechanism (CCM) of Trichodesmium showed that carboxylation rates are modulated by HCO3- and pH. The decrease in assimilation of inorganic carbon (Ci) at low CO2, when TIC was varied, was due to HCO3- uptake limitation of the carboxylation rate. Conversely, when pH was varied, Ci assimilation declined due to a high-pH mediated increase in HCO3- and CO2 leakage rates, potentially coupled to other processes (uncharacterised within the CCM model) that restrict Ci assimilation rates under high-pH conditions.

SUBMITTER: Boatman TG

PROVIDER: S-EPMC6022602 | biostudies-literature | 2018 Jun

REPOSITORIES: biostudies-literature

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Inorganic carbon and pH dependency of photosynthetic rates in Trichodesmium.

Boatman Tobias G TG Mangan Niall M NM Lawson Tracy T Geider Richard J RJ

Journal of experimental botany 20180601 15

Increasing atmospheric CO2 concentrations are leading to increases in dissolved CO2 and HCO3- concentrations and decreases in pH and CO32- in the world's oceans. There remain many uncertainties as to the magnitude of biological responses of key organisms to these chemical changes. In this study, we established the relationship between photosynthetic carbon fixation rates and pH, CO2, and HCO3- concentrations in the diazotroph, Trichodesmium erythraeum IMS101. Inorganic 14C-assimilation was measu ...[more]

PMID: 29659983

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Project description:Microalgae and cyanobacteria are considered as important model organisms to investigate the biology of photosynthesis; moreover, they are valuable sources of biomolecules for several biotechnological applications. Understanding the species-specific traits of photosynthetic electron transport is extremely important, because it contributes to the regulation of ATP/NADPH ratio, which has direct/indirect links to carbon fixation and other metabolic pathways and thus overall growth and biomass production. In the present work, a cuvette-based setup is developed, in which a combination of measurements of dissolved oxygen, pH, chlorophyll fluorescence and NADPH kinetics can be performed without disturbing the physiological status of the sample. The suitability of the system is demonstrated using a model cyanobacterium Synechocystis sp. PCC6803, as well as biofuel-candidate microalgae species, such as Chlorella sorokiniana, Dunaliella salina and Nannochloropsis limnetica undergoing inorganic carbon (Ci) limitation. Inorganic carbon limitation, induced by photosynthetic Ci uptake under continuous illumination, caused a decrease in the effective quantum yield of PSII (Y(II)) and loss of oxygen-evolving capacity in all species investigated here; these effects were largely recovered by the addition of NaHCO3. Detailed analysis of the dark-light and light-dark transitions of NADPH production/uptake and changes in chlorophyll fluorescence kinetics revealed species- and condition-specific responses. These responses indicate that the impact of decreased Calvin-Benson cycle activity on photosynthetic electron transport pathways involving several sections of the electron transport chain (such as electron transfer via the QA-QB-plastoquinone pool, the redox state of the plastoquinone pool) can be analyzed with high sensitivity in a comparative manner. Therefore, the integrated system presented here can be applied for screening for specific traits in several significant species at different stages of inorganic carbon limitation, a condition that strongly impacts primary productivity.

Project description:Synechocystis 6803 cells was grown photoautotrophically at 32 °C buffered in BG-11 and bubbled with 3% CO2. A relatively mild Ci stress was applied by switching the aeration from 3% CO2 to air alone. After incubation under designated conditions, a 100-ml aliquot of culture was immediately combined with an equal volume of ice-cold mixture of phenol and ethanol (1:10, w/v) in an ice bath. The resultant cells were collected by centrifugation at 1000 x g for 10 min at 4 °C. Total RNA was isolated with RNeasy Midi Kit (Qiagen, Valencia, CA) and further treated with the DNA-free kit (Ambion, Austin, TX). Fluorescently labeled cDNA was produced via a two-step indirect procedure involving cDNA synthesis from 16 µg of total RNA in a reverse transcriptase reaction incorporating aminoallyl-modified deoxynucleotide, followed by the second step involving chemical coupling of fluorescent dye to the introduced amino moieties of the synthesized cDNA. Labeled cDNA were adjusted to 14.75 µl, and the remainder of the hybridization components containing 2.5 µl of 10 µg µl-1 salmon sperm DNA, 8.75 µl of 20x SSC, 0.25 µl of 10% SDS, and 8.75 µl of formamide were added. The mixture was then heated for 2 min at 99 °C and maintained at 42 °C until hybridization. Hybridizations were preformed in a static incubator at 42 °C for 12-16 h then washed by placing in a 250-ml solution of 2x SSC and 0.1% SDS at 42 °C for 5 min with gentle agitation provided by rotation of a magnetic stir bar. The slide was transferred quickly to a 250-ml solution of 0.1x SSC and 0.1% SDS, incubated for 10 min at room temperature with gentle agitation, and washed five additional times in 0.1x SSC for 1 min at room temperature. Hybridization signals from the microarray were quantified using GenePix Pro 4.1 (Axon Instruments, Union City, CA). The quality control procedures were conducted in the image analysis software, and then data were saved to Acuity 3.1 (Axon Instruments). Keywords: time-course

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Inorganic carbon and pH dependency of photosynthetic rates in Trichodesmium.

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Inorganic carbon and pH dependency of photosynthetic rates in Trichodesmium.

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