Photosynthesis evolution in Cyanobacteria Zahn, Laura M
Science (American Association for the Advancement of Science),
2017-Mar-31, 2017-03-31, 20170331, Letnik:
355, Številka:
6332
Journal Article
Most investigations of biogeochemically important microbes have focused on plastic (short-term) phenotypic responses in the absence of genetic change, whereas few have investigated adaptive ...(long-term) responses. However, no studies to date have investigated the molecular progression underlying the transition from plasticity to adaptation under elevated CO2 for a marine nitrogen-fixer. To address this gap, we cultured the globally important cyanobacterium Trichodesmium at both low and high CO2 for 4.5 y, followed by reciprocal transplantation experiments to test for adaptation. Intriguingly, fitness actually increased in all high-CO2 adapted cell lines in the ancestral environment upon reciprocal transplantation. By leveraging coordinated phenotypic and transcriptomic profiles, we identified expression changes and pathway enrichments that rapidly responded to elevated CO2 and were maintained upon adaptation, providing strong evidence for genetic assimilation. These candidate genes and pathways included those involved in photosystems, transcriptional regulation, cell signaling, carbon/nitrogen storage, and energy metabolism. Conversely, significant changes in specific sigma factor expression were only observed upon adaptation. These data reveal genetic assimilation as a potentially adaptive response of Trichodesmium and importantly elucidate underlying metabolic pathways paralleling the fixation of the plastic phenotype upon adaptation, thereby contributing to the few available data demonstrating genetic assimilation in microbial photoautotrophs. These molecular insights are thus critical for identifying pathways under selection as drivers in plasticity and adaptation.
Many carbon-fixing bacteria rely on a CO sub(2) concentrating mechanism (CCM) to elevate the CO sub(2) concentration around the carboxylating enzyme ribulose bisphosphate carboxylase/oxygenase ...(RuBisCO). The CCM is postulated to simultaneously enhance the rate of carboxylation and minimize oxygenation, a competitive reaction with O sub(2) also catalyzed by RuBisCO. To achieve this effect, the CCM combines two features: active transport of inorganic carbon into the cell and colocalization of carbonic anhydrase and RuBisCO inside proteinaceous microcompartments called carboxysomes. Understanding the significance of the various CCM components requires reconciling biochemical intuition with a quantitative description of the system. To this end, we have developed a mathematical model of the CCM to analyze its energetic costs and the inherent intertwining of physiology and pH. We find that intracellular pH greatly affects the cost of inorganic carbon accumulation. At low pH the inorganic carbon pool contains more of the highly cell-permeable H sub(2)CO sub( 3), necessitating a substantial expenditure of energy on transport to maintain internal inorganic carbon levels. An intracellular pH approximately 8 reduces leakage, making the CCM significantly more energetically efficient. This pH prediction coincides well with our measurement of intracellular pH in a model cyanobacterium. We also demonstrate that CO sub(2) retention in the carboxysome is necessary, whereas selective uptake of HCO sub(3)- into the carboxysome would not appreciably enhance energetic efficiency. Altogether, integration of pH produces a model that is quantitatively consistent with cyanobacterial physiology, emphasizing that pH cannot be neglected when describing biological systems interacting with inorganic carbon pools.
Global population growth is projected to outpace plant-breeding improvements in major crop yields within decades. To ensure future food security, multiple creative efforts seek to overcome ...limitations to crop yield. Perhaps the greatest limitation to increased crop yield is photosynthetic inefficiency, particularly in C sub(3) crop plants. Recently, great strides have been made toward crop improvement by researchers seeking to introduce the cyanobacterial CO sub(2)-concentrating mechanism (CCM) into plant chloroplasts. This strategy recognises the C sub(3) chloroplast as lacking a CCM, and being a primordial cyanobacterium at its essence. Hence the collection of solute transporters, enzymes, and physical structures that make cyanobacterial CO sub(2)-fixation so efficient are viewed as a natural source of genetic material for C sub(3) chloroplast improvement. Also we highlight recent outstanding research aimed toward the goal of introducing a cyanobacterial CCM into C sub(3) chloroplasts and consider future research directions.
This photobioreactor study investigated the influence of CO sub(2) aeration on biomass production, carbon dioxide fixation rate, pH, cell's essential elements such as carbon, nitrogen, and hydrogen, ...as well as lipid content, whilst under a range of luminescence-modified lighting conditions. The effect of aeration with pure air (comprising 0.03% CO sub(2)) on the CO sub(2) fixation rate was insignificant compared to the higher concentrations used. Results showed that, with the exception of blue PBR, increasing CO sub(2) concentrations in the air stream enhanced the fixation rate of CO sub(2) in C. vulgaris. Cyanobacteria cells showed significant tolerance to 15% CO sub(2). The results obtained demonstrated that the combination of blue light and 15% CO sub(2) provided a condition in which higher rates of lipid accumulation was induced in both algal strains. The highest lipid content observed at this condition was 36.6% obtained in G. membrancea. Aeration with 15% CO sub(2) enhanced lipid production of G. membranacea, to at least twice the amount produced at 5% CO sub(2) in all photobioreactors. The most significant difference between the 5% and 15% CO sub(2) aeration conditions was observed in the yellow PBR, in which the lipid content was enhanced up to six times.
From April 2012 to January 2013 (over four seasons), in situ microcosm experiments were conducted in Lake Taihu, perturbed over a range of pCO sub(2) scenarios (270, 380, and 750 mu atm; 1 atm = ...101.325 kPa). The influence of CO sub(2) level on microcosms was greatest during the spring because of the high growth rate of phytoplankton. In this season, rising CO sub(2) levels caused a pH reduction, and the maximum reduction was 0.6 units when CO sub(2) level was enhanced from the present level to 750 mu atm. The doubling of CO sub(2) level could increase the net primary production (NPP) by 65% during spring when the concentrations of other nutrients were maintained. The rise of NPP could cause a decline of dissolved inorganic carbon (DIC) concentration, and CO sub(2) enrichment might mitigate the extent of this decline. Meanwhile, higher CO sub(2) may slow or prevent a loss of diversity of phytoplankton in microcosms in this season. During the other three seasons, Microcystis predominated, and the percentage of cyanobacteria did not alter with the change of CO sub(2). We did not observe a significant increase in the abundance of any taxa with the rise of CO sub(2) during the in situ microcosm experiments.Original Abstract: D'avril 2012 a janvier 2013 (quatre saisons), des experiences en microcosmes in situ ont ete menees dans le lac Taihu, les microcosmes etant perturbes de maniere a couvrir une fourchette de scenarios de pCO sub(2) (270, 380 et 750 mu atm; 1 atm = 101.325 kPa). L'influence des niveaux de CO sub(2) sur les microcosmes etait la plus grande au printemps en raison du taux de croissance eleve du phytoplancton. Durant cette saison, l'augmentation des concentrations de CO sub(2) causait une reduction du pH, la reduction maximum etant de 0,6 unite quand la concentration de CO sub(2) etait rehaussee a 750 mu atm. Le fait de doubler la concentration de CO sub(2) pouvait se traduire par une augmentation de 65 % de la production primaire nette (PPN) au printemps, quand les concentrations d'autres nutriments etaient maintenues constantes. L'augmentation de la PPN pouvait causer une diminution de la concentration de carbone inorganique dissous (CID) dans l'eau et l'augmentation du CO sub(2) pouvait attenuer l'ampleur de cette diminution. Par ailleurs, des teneurs en CO sub(2) plus elevees pouvaient ralentir ou empecher une baisse de diversite du phytoplancton dans les microcosmes durant cette saison. Durant les trois autres saisons, Microcystis predominait, et le pourcentage de cyanobacteries ne variait pas en fonction de la concentration de CO sub(2). Aucune augmentation significative de l'abondance d'un taxon associee a l'augmentation du CO sub(2) durant les experiences en microcosmes in situ n'a ete observee. Traduit par la Redaction
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