Environmental regulation of CO 2 -concentrating mechanisms in microalgae (original) (raw)
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The impact of environmental factors on carbon dioxide fixation by microalgae
FEMS Microbiology Letters, 2017
Microalgae are among the most productive biological systems for converting sunlight into chemical energy, which is used to capture and transform inorganic carbon into biomass. The efficiency of carbon dioxide capture depends on the cultivation system configuration (photobioreactors or open systems) and can vary according to the state of the algal physiology, the chemical composition of the nutrient medium, and environmental factors such as irradiance, temperature and pH. This mini-review is focused on some of the most important environmental factors determining photosynthetic activity, carbon dioxide biofixation, cell growth rate and biomass productivity by microalgae. These include carbon dioxide and O 2 concentrations, light intensity, cultivation temperature and nutrients. Finally, a review of the operation of microalgal cultivation systems outdoors is presented as an example of the impact of environmental conditions on biomass productivity and carbon dioxide fixation.
Active transport of CO2 by three species of marine microalgae
Journal of Phycology, 2001
The occurrence of an active CO 2 transport system and of carbonic anhydrase (CA) has been investigated by mass spectrometry in the marine, unicellular rhodophyte Porphyridium cruentum (S.F. Gray) Naegeli and two marine chlorophytes Nannochloris atomus Butcher and Nannochloris maculata Butcher. Illumination of darkened cells incubated with 100 M H 13 CO 3 Ϫ caused a rapid initial drop, followed by a slower decline in the extracellular CO 2 concentration. Addition of bovine CA to the medium raised the CO 2 concentration by restoring the HCO 3 Ϫ -CO 2 equilibrium, indicating that cells were taking up CO 2 and were maintaining the CO 2 concentration in the medium below its equilibrium value during photosynthesis. Darkening the cell suspensions caused a rapid increase in the extracellular CO 2 concentration in all three species, indicating that the cells had accumulated an internal pool of unfixed inorganic carbon. CA activity was detected by monitoring the rate of exchange of 18 O from 13 C 18 O 2 into water. Exchange of 18 O was rapid in darkened cell suspensions, but was not inhibited by 500 M acetazolamide, a membrane-impermeable inhibitor of CA, indicating that external CA activity was not present in any of these species. In all three species, the rate of exchange was completely inhibited by 500 M ethoxyzolamide, a membrane-permeable CA-inhibitor, showing that an intracellular CA was present. These results demonstrate that the three species are capable of CO 2 uptake by active transport for use as a carbon source for photosynthesis.
Plant, Cell and Environment, 1999
As previously described, the absolute rate of photosynthesis due to a limited concentration of dissolved inorganic carbon at alkaline pH, where the rate of CO 2 formation is strictly limited, plotted as a function of chlorophyll (Chl) concentration, will take the form of a rectangular hyperbola combined with a linear rate directly proportional to [Chl], which are, respectively, due to the contribution of CO 2 and HCO 3 to photosynthesis. This model represents that the mathematical asymptote of absolute rate of photosynthesis versus cell density is described by the whole-cell rate constant for HCO 3 uptake and the maximum rate of CO 2 formation in the extracellular space. This means that any trace modification of the CO 2 formation rate outside the cell will alter the photosynthetic rate and should be detectable experimentally. In air-grown Chlorella ellipsoidea and C. kessleri and in high CO 2-grown C. saccharophila, the graph of the absolute rate of photosynthesis against [Chl] clearly followed the mathematical model described above and the actual CO 2 formation rates outside the cells were not significantly different from the calculated rates. It also indicated that the whole-cell rate constants for CO 2 and HCO 3 uptake in air-grown C. ellipsoidea and C. saccharophila were similar at ≈ 300 and 2•0 mm 3 µg-1 Chl min-1 , respectively, whereas those in air-grown C. kessleri were ≈ 550 and 15 mm 3 µg-1 Chl min-1. These results indicate that no acidification of the periplasmic space occurs, and there is no trace activity of external carbonic anhydrase in these microalgae.
Physiological responses of carbon-sequestering microalgae to elevated carbon regimes
European Journal of Phycology, 2016
In order to identify a high carbon-sequestering microalgal strain, the physiological effect of different concentrations of carbon sources on microalgae growth was investigated. Five indigenous strains (I-1, I-2, I-3, I-4 and I-5) and a reference strain (I-0: Coccolithus pelagicus 913/3) were subjected to CO 2 concentrations of 0.03-15% and NaHCO 3 of 0.05-2 g CO 2 l-1. The logistic model was applied for data fitting, as well as for estimation of the maximum growth rate (μ max) and the biomass carrying capacity (B max). Amongst the five indigenous strains, I-3 was similar to the reference strain with regards to biomass production values. The B max of I-3 significantly increased from 214 to 828 mg l-1 when CO 2 concentration was increased from 0.03 to 15% (r = 0.955, P = 0.012). Additionally, the B max of I-3 increased with increasing NaHCO 3 (r = 0.885, P = 0.046) and was recorded at 153 mg l-1 (at 0.05 g CO 2 l-1) and 774 mg l-1 at (2 g CO 2 l-1). Relative electron transport rate (rETR) and maximum quantum yield (F v /F m) were also applied to assess the impact of elevated carbon sources on the microalgal cells at the physiological level. Isolate I-3 displayed the highest rETR confirming its tolerance to higher quantities of carbon. Additionally, the decline in F v /F m with increasing carbon was similar for strains I-3 and the reference strain. Based on partial 28s ribosomal RNA gene sequencing, strain I-3 was homologous to the ribosomal genes of Chlorella sp.
Sustainability
The rising concentration of global atmospheric carbon dioxide (CO2) has severely affected our planet’s homeostasis. Efforts are being made worldwide to curb carbon dioxide emissions, but there is still no strategy or technology available to date that is widely accepted. Two basic strategies are employed for reducing CO2 emissions, viz. (i) a decrease in fossil fuel use, and increased use of renewable energy sources; and (ii) carbon sequestration by various biological, chemical, or physical methods. This review has explored microalgae’s role in carbon sequestration, the physiological apparatus, with special emphasis on the carbon concentration mechanism (CCM). A CCM is a specialized mechanism of microalgae. In this process, a sub-cellular organelle known as pyrenoid, containing a high concentration of Ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco), helps in the fixation of CO2. One type of carbon concentration mechanism in Chlamydomonas reinhardtii and the association of p...
How Do Algae Concentrate CO2 to Increase the Efficiency of Photosynthetic Carbon Fixation
Plant Physiology, 1999
The ability of photosynthetic organisms to use CO 2 for photosynthesis depends in part on the properties of Rubisco. Rubisco has a surprisingly poor affinity for CO 2 , probably because it evolved in an atmosphere that had very high CO 2 levels compared with the present atmosphere. In C 3 plants the K m (CO 2 ) of Rubisco ranges between 15 and 25 m. In cyanobacteria Rubisco has an even lower affinity for CO 2 , and the K m (CO 2 ) can be greater than 200 m. In comparison, the concentration of CO 2 in water in equilibrium with air is approximately 10 m. From these numbers it becomes apparent that Rubisco is operating at no more than 30% of its capacity under standard atmospheric conditions. This is one of the reasons that C 3 plants contain such large amounts of Rubisco. Exacerbating this situation is the fact that O 2 is a competitive substrate with respect to CO 2 .
Maximum-CO 2 Tolerance in Microalgae: Possible Mechanisms and Higher lipid Accumulation
Vaibhav Nagaich Microalgae are belonging to unicellular or simple multicellular photosynthetic microorganisms that have the capability to fix CO 2 from various sources, industrial exhaust gases, with the environment and soluble carbonate salts. Unbalanced production of the environment CO 2 constitutes a most important challenge to worldwide sustainability. Photoautotrophic algal cultures have the possible to lessen the release of CO 2 into the environment by CO 2 fixation, helping alleviate the trend toward global warming. Increased CO 2 concentration improved significantly the growth rate of the species. In this study, the effects of nitrate feeding on microalgal growth and related CO 2 fixation were evaluated, as a affinity to increase carbon fixation. The present study aimed at investigating the mechanisms of carbon dioxide fixation in microalgal cultivation. Biomass composition accessible a prevalence of proteins but also a high amount of lipids. The Rubisco give the high greate...