Presentation on theme: "CO 2 Concentrating Mechanisms (CCM) in Algae By: Reza Taheri Tehrani Supervisor: Dr. Shariati."— Presentation transcript:
CO 2 Concentrating Mechanisms (CCM) in Algae By: Reza Taheri Tehrani Supervisor: Dr. Shariati
Headlines: Why do some algae need CO 2 concentrating mechanisms (CCM)? The evidences for existence of CCM in algae A general model for CCM in algae The types of CCM in algae Modulation of CCM by environmental factors
Why do some algae need CO 2 concentrating? Aquatic photosynthetic microorganisms account for almost 50% of the world’s photosynthesis. These organisms face several challenges in acquiring and fixing CO 2 as follows: 1.the Km( CO 2 ) of Rubisco in C 3 plants and cyanobacteria is 20 µM and 200 µM respectively. 2.inorganic carbon concentration and diffusion rate in the water is much less than air. 3.In algae, Rubisco is operating at no more than 30% of its capacity. Slide Num: 3
CO 2 concentrating can solve this problem Microalgae (like to C 4 and CAM plants) have developed ways to concentrate the CO 2 at the location of Rubisco. CO2 concentrating mechanisms (CCM) is a biological adaptation to low CO2 concentration. Some algae can concentrate CO 2 within the cell more than 100 fold over ambient CO 2 levels Slide Num:4
Evidence for CO 2 Concentrating 1.Algae have the ability to efficiently ﬁx CO 2 even in low external CO2 concentration. 2. Ci uptake has been measured directly in a number of laboratories, and the Ci concentration inside the cell is higher than can be accounted for by diffusion alone. 3. Further evidence comes from mutant studies. Mutant strains that grew well on elevated CO 2 but poorly on low CO 2 has been yielded mutants in CCMs Slide Num: 5
General model for CO 2 concentrating Algae with CO 2 concentrating ability have certain common properties that allow them to use CO 2 efficiently. A. Rubisco packaging in a very specific compartment (carboxysome and pyrenoid) B. The ability to accumulate C i ( inorganic carbon= CO 2 + HCO 3 - ). C. presence of a CA (carbonic anhydrase) near the location of Rubisco. Slide Num:6
Slide Num: 7 General model for CO 2 concentrating: Above: in cyanobacteria Below: in a eukaryotic algae cCA: chlorpalstinc carbonic anhydrse pCA: periplasmic CA PGA: 3-phophoglyceric acid
A. Rubisco packaging Slide Num: 8 In most microalgae (in contrast to higher plant) Rubisco is concentrated in a specific location, carboxysome and pyrenoid. The carboxysome is the specialized compartment that is surrounded by a protein shell.
Slide Num: 9 Electron micrograph of the carboxysome in a cyanobacteria
Slide Num: 10 In microalgae, Rubisco is also packaged in pyrenoid. The amount of Rubisco in the pyrenoid varied with growth and nutrient conditions Left, Electron micrograph of the pyrenoid in a green alga Right, Immunogold labeling of the pyrenoid.
Slide Num: 11 Pyrenoids (P) from C.reinhardtii in high CO 2 (A) and low CO 2 concentration (B).
B. The ability to accumulate C i Algae display a variety of ways to concentrate CO 2 as follows: 1.C 4 mechanisms 2.Active transport of C i ( inorganic carbon= CO 2 + HCO 3 - ) 3.pH gradient in chloroplast. Slide Num:12
1 st CCM type: C 4 mechanisms in algae C 4 photosynthesis and CAM in terrestrial higher plants were the ﬁrst photosynthetic CCMs to be described in detail. The presence of C 4 or CAM-like metabolism has been observed in submerged aquatic plants and algae. Slide Num: 13 A schematic model for C 4 -like mechanism in eukaryotic algal cells
2nd CCM type: Active transport of C i Algae have a CCM which involves a variety of active CO 2 and HCO 3 - uptake systems. Slide Num: 14
Ci transporters in cyanobacteria NameUptakeConditionPlaceaffinitycomment BCT1HCO 3 - C i deficiencyPmH. ANa + independent BicAHCO 3 - constitutivePmL. ANa + dependent SbtAHCO 3 - C i deficiencyPmH. ANa + dependent NDH1 3 CO 2 C i deficiencyTylH. ACA activity NDH1 4 CO 2 ConstitutivePmL. ACA like Slide Num: 15 At least ﬁve distinct C i transport systems are known for cyanobacteria with low and high affinity for C i. C i = inorganic carbon H.A= high affinity L.A= low affinity
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Slide Num: 17 Changing in transporters under C i limitation
Slide Num:18 3 rd CCM type : pH gradient in chloroplast. This type of CCM found in eukaryotic algae relies on the pH gradient across the thylakoid membrane in the light.
CO 2 can easily diffuse through biological membranes. Microalgae are composed of only one or a few cells and ready access to the environment. Microalgae overcome the problem of CO 2 diffusion by accumulating a charged species (HCO 3 - ) that diffuses much more slowly than CO 2. CA converts HCO 3 - to CO 2 that is the substrate required by Rubisco. Slide Num:19 Leakage and regeneration of CO 2
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C. Role of CA (Carbonic Anhydrase) in CO 2 regeneration The role of CA is the dehydration of accumulated HCO 3 in order to elevate concentration of CO 2 in the carboxysome. HCO 3 - + H + H 2 CO 3 CO 2 + H 2 O Loss of CA leads to a cell that cannot grow well on limiting levels of CO 2 while accumulate HCO 3 - to higher levels than wild type cells Slide Num:21
more about CA A transformed species with a human CA requires high CO 2 for growth. The human CA is localized to the cytoplasm and converts the accumulated HCO 3 _ to CO 2 that leake from the cell and could not beused efficiently for photosynthesis. The location of the internal CA is as important as the packaging of Rubisco. Slide Num:22
CCMs modulation Environmental conditions and nutrient availability play a signiﬁcant role in modulating CCM activity. Macronutrient deﬁciency can affect photosynthesis so understanding the interactions between CCM activity, Environmental conditions, and nutrient availability is important. The amount of acquiring carbon through a CCM is coupled to the availability of other nutrients. Slide Num:23
phosphorus limitation would affect CCMs because of the dependency of C i on ATP supply. Zinc is used as the metal cofactor of CA and is directly involved in the catalytic mechanism of these enzymes thus, it can be expected that a reduction in Zn availability would affect CCMs Iron can often compromise light-harvesting processes and photosynthesis. Slide Num: 24 Nutrients
Conclusion 1.Rubisco biochemical properties and aquatic condition are the most important reasons that algae need to CCM 2.CCM is a biological adaptation to low carbon dioxide concentrations in the environment 3.Rubisco packaging, CO 2 concentrating, and CA operating are essential for a perfect CCM. 4.CO 2 concentrating (at least) has three types; C 4 like, active transport and pH gradient in chloroplast. 5.CCM can be modulated by environmental factors and nutritions. Slide Num: 25
Thank you for your attention The file of presentation may be downloaded from following link: http://sci.ui.ac.ir/~reza_taheri/