5. Conclusions
Deep sea hydrothermal vents are isolated habitats that contain many unique organisms of the three domains of life; archaea, bacteria and eukarya. Most microbial communities in these habitats have the capability to fix inorganic carbon dioxide. Five CO2 fixation pathways have been documented as important in hydrothermal habitats; the Calvin-Benson cycle, reductive tricarboxylic acid cycle, reductive acetyl-CoA pathway, dicarboxylate/4-hydroxybutyrate cycle and 3-hydroxypropionate/4-hydroxybutyrate cycle. Four different forms of RuBisCO, designated as I, II, III and IV, operate in different microbial communities associated with deep sea hydrothermal vents. The rTCA cycle is found in the Epsilonproteobacteria and Aquificales and the reductive acetyl-CoA pathway in the methanogens microorganisms. It appears that the 3-HP/4-hydroxybutyrate is potentially an important carbon fixation pathway for archaeal communities in deep-sea hydrothermal vent environments. In addition to these pathways for the direct fixation of carbon dioxide, carbonic anhydrase catalyzes the interconversion of CO2 and HCO3−, and facilitates inorganic carbon dioxide uptake, fixation and assimilation. The bicarbonate formed by CA is an essential growth factor for microorganisms and is a metabolic precursor for many other compounds.
Human activities have significantly increased the atmospheric carbon dioxide concentration and this is an important cause of global warming. Therefore, it is of interest to find technologies for carbon dioxide capture. These technologies, combined with other efforts, could help stabilize greenhouse gas concentrations in the atmosphere and mitigate climate change. Biological CO2 fixation has attracted much attention as an alternative strategy. It can be done by plants and by photosynthetic and chemosynthetic microorganisms. These biological technologies could also be attractive for production of biofuels or other industrial products. A variety of technological solutions have been proposed for CO2 sequestration systems. In addition, a number of technologies are currently employed or under development to separate carbon dioxide from mixed byproduct streams of large stationary anthropogenic sources. Therefore, a variety of reactors containing an enzyme such as carbonic anhydrase have been designed to extract CO2 from mixed gas.
In order to develop and improve new technologies, it is important to search and explore enzymes from different sources. The organisms of deep sea hydrothermal vents are well adapted to fix carbon dioxide in an unusual range of temperatures, pressure condition, pH and metal toxicity. So, organisms from the environment could be used for engineering microbes to solve the various technology options for carbon capture and storage.