Natural carbon fixation and advances in synthetic engineering for redesigning and creating new fixation pathways.

Carbon circulation on Earth. Anthropogenic and natural carbon emissions and carbon sequestration routes. [Display omitted] • Carbon is often negatively associated with the anthropogenic emissions of greenhouse gases and, consequently, with environmental issues such as global warming. However, carbon is an element of paramount importance for life and ecological processes. • The knowledge of carbon fixation cycles, in addition to the ecological and evolutionary studies on the emergence of the first beings that inhabited Earth and metabolized carbon, provides a detailed understanding of the enzymes and important intermediaries involved in these cycles. • The central carbon metabolizing enzymes can be used for a variety of purposes; artificial CO 2 fixation pathways can be designed and implemented in suitable host organisms; new solutions are possible for manipulating carbon fixation pathways and increasing their final yields. • The multidisciplinary integration of omics, synthetic biology, molecular biology, and biochemistry can enable the scientific community to describe new carbon fixation pathways and predict important routes and enzymes involved in these processes. This integration may further provide guidance for overcoming the limitations of natural carbon fixation pathways and allow the development of biotechnological applications. • Investigating thermophilic microorganisms is crucial for understanding many evolutionary events. These microorganisms are investigated extensively for developing biotechnological applications because of their metabolic diversity. • In addition to the six well-known natural carbon fixation pathways, the development of omics and systems biology has spearheaded the discovery of new natural and synthetic pathways for carbon metabolism. Autotrophic carbon fixation is the primary route through which organic carbon enters the biosphere, and it is a key step in the biogeochemical carbon cycle. The Calvin–Benson–Bassham pathway, which is predominantly found in plants, algae, and some bacteria (mainly cyanobacteria), was previously considered to be the sole carbon-fixation pathway. However, the discovery of a new carbon-fixation pathway in sulfurous green bacteria almost two decades ago encouraged further research on previously overlooked ancient carbon-fixation pathways in taxonomically and phylogenetically distinct microorganisms. In this review, we summarize the six known natural carbon-fixation pathways and outline the newly proposed additions to this list. We also discuss the recent achievements in synthetic carbon fixation and the importance of the metabolism of thermophilic microorganisms in this field. Currently, at least six carbon-fixation routes have been confirmed in Bacteria and Archaea. Other possible candidate routes have also been suggested on the basis of emerging "omics" data analyses, expanding our knowledge and stimulating discussions on the importance of these pathways in the way organisms acquire carbon. Notably, the currently known natural fixation routes cannot balance the excessive anthropogenic carbon emissions in a highly unbalanced global carbon cycle. Therefore, significant efforts have also been made to improve the existing carbon-fixation pathways and/or design new efficient in vitro and in vivo synthetic pathways. [ABSTRACT FROM AUTHOR]