Metagenomics-guided analysis of microbial chemolithoautotrophic phosphite oxidation yields evidence of a seventh natural CO ₂ fixation pathway

Abstract

Dissimilatory phosphite oxidation (DPO), a microbial metabolism by which phosphite (HPO) is oxidized to phosphate (PO), is the most energetically favorable chemotrophic electron-donating process known. Only one DPO organism has been described to date, and little is known about the environmental relevance of this metabolism. In this study, we used 16S rRNA gene community analysis and genome-resolved metagenomics to characterize anaerobic wastewater treatment sludge enrichments performing DPO coupled to CO reduction. We identified an uncultivated DPO bacterium, Phosphitivorax ( P.) anaerolimi strain Phox-21, that belongs to candidate order GW-28 within the , which has no known cultured isolates. Genes for phosphite oxidation and for CO reduction to formate were found in the genome of P. anaerolimi, but it appears to lack any of the known natural carbon fixation pathways. These observations led us to propose a metabolic model for autotrophic growth by P. anaerolimi whereby DPO drives CO reduction to formate, which is then assimilated into biomass via the reductive glycine pathway.

GapMind: Automated annotation of amino acid biosynthesis

“…Recent work has suggested that some bacteria can synthesize glycine directly from carbon dioxide and ammonia by using the glycine cleavage system in reverse to convert CO 2 , ammonia, 5,10-methylenetetrahydrofolate, and NADH to glycine, tetrahydrofolate, and NAD+ (Figueroa et al 2018;Tveit et al 2019) . Serine hydroxymethyltransferase (in the reverse of the usual direction) could then form serine.…”

Genetic evidence for two carbon fixation pathways in symbiotic and free-living bacteria: The Calvin-Benson-Bassham cycle and the reverse tricarboxylic acid cycle

“…Primary production by autotrophic organisms drives the global carbon cycle. Currently, seven naturally occurring pathways for inorganic carbon fixation are known in autotrophic organisms (1). The dominant carbon fixation pathway used by plants, algae, and many bacteria is the Calvin-Benson-Bassham (CBB) cycle.…”

Horizontal acquisition of a patchwork Calvin cycle by symbiotic and free-living Campylobacterota (formerly Epsilonproteobacteria)

“…All life on earth is based on carbon fixation, and its molecular machinery is increasingly becoming a focus of biotechnology and geo-engineering efforts due to its potential to improve crop yields and sequester carbon dioxide from the atmosphere 1 . Seven carbon fixation pathways have evolved in nature, and one purely synthetic pathway runs in vitro 2–4 . Of the six natural pathways, the Calvin-Benson-Bassham (CBB) cycle was the first discovered, and is believed to be the most widespread 5–7 .…”