Article

A 3-Hydroxypropionate/4-Hydroxybutyrate Autotrophic Carbon Dioxide Assimilation Pathway in Archaea

Mikrobiologie, Fakultät Biologie, Universität Freiburg, Schänzlestrasse 1, D-79104 Freiburg, Germany.
Science (Impact Factor: 33.61). 07/2008; 318(5857):1782-6. DOI: 10.1126/science.1149976
Source: PubMed

ABSTRACT

The assimilation of carbon dioxide (CO2) into organic material is quantitatively the most important biosynthetic process. We discovered that an autotrophic member
of the archaeal order Sulfolobales, Metallosphaera sedula, fixed CO2 with acetyl–coenzyme A (acetyl-CoA)/propionyl-CoA carboxylase as the key carboxylating enzyme. In this system, one acetyl-CoA
and two bicarbonate molecules were reductively converted via 3-hydroxypropionate to succinyl-CoA. This intermediate was reduced
to 4-hydroxybutyrate and converted into two acetyl-CoA molecules via 4-hydroxybutyryl-CoA dehydratase. The key genes of this
pathway were found not only in Metallosphaera but also in Sulfolobus, Archaeoglobus, and Cenarchaeum species. Moreover, the Global Ocean Sampling database contains half as many 4-hydroxybutyryl-CoA dehydratase sequences as
compared with those found for another key photosynthetic CO2-fixing enzyme, ribulose-1,5-bisphosphate carboxylase-oxygenase. This indicates the importance of this enzyme in global carbon
cycling.

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    • "Recently discovered in the domain Archaea are the 3-hydroxypropio- nate / 4-hydroxybutyrate cycle (Berg et al., 2007) and the dicarboxylate / 4-hydroxybutyrate cycle (Huber et al., 2008), which are formed, as suggested (Marakushev and Belonogova, 2011) in the later divergent evolution of the original CAF bicycle. Logically, it becomes reasonable to assume that the reduced, non-closed reductive citrate pathway described in heliobacteria (Pickett et al., 1994; Sattley et al., 2008), as well as the reductive acetyl-CoA pathway in methanogenic archaea and acetate-producing clostridia (Ljungdahl and Wood, 1965; Wood, 1991; Ljungdahl, 2009) are also the result of the development of the CAF bicycle. "
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    • "M. sedula and the Sulfolobus species grow well at low pH, a significant advantage for production of acidic products such as lactic and 3-hydroxypropionic acids, which are easier to purify in their protonated forms (Maris et al., 2004). M. sedula's ability to solubilize metals by oxidizing them has applications in bioleaching, while its novel carbon-fixation pathway (Berg et al., 2007) offers a potential alternative to the RuBisCo-dependent Calvin Cycle for carbon-capture applications. Fuels are typically highly reduced organic molecules, so various efforts to maximize biofuel titers have focused on tuning the redox pathways within mesophilic hosts to favor the production of reduced end products (Liu et al., 2015). "
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