Bacteria can be great allies in the fight against climate change. A team of researchers has discovered a cyanobacterium that can feed on CO2 at much higher rates than others.
The bacterial species joins an already large list of microbes that have evolved naturally to absorb CO2 as an efficient way to remove the greenhouse gas from the atmosphere.
Science is looking for possible applications for these organisms in the context of combating the climate crisis. Recent studies have suggested that bacteria could also produce useful chemicals in addition to capturing CO2.
Introduction
The ability to sequester and fix CO2 is common to plants and microalgae (1), however, bacteria have many competitive advantages, including a high growth rate and significantly faster life cycle, the ability to exist in a high-density culture, and the ability to be easily genetically engineered.
Bacteria, moreover, just like other microbes, can produce a wide range of useful compounds for industry and ecosystem protection.
The discovery of cyanobacterium
In September 2022, a cyanobacterium capable of turning CO2 into biomass faster than any other known organism was discovered.
The expedition led by the team of the ‘2Frontiers Project.’ (2) together with researchers from the University of Palermo, aimed precisely at studying the particular ecosystem of the Bay of Levante, located next to the Aeolian island of Vulcano, which is characterized by unique shallow carbon seeps and a gradient of dissolved carbon dioxide that comes from volcanic seeps at extremely low pH.
The escaping carbon fills the water, creating a rare ecosystem that contains as yet unknown life forms.
2 Frontiers Projects
The discovery of cyanobacterium is part of one of the pivotal projects of the ‘2Frontiers Project‘ or (2FP), CARBON 1.
The 2FP is a research initiative bringing together a team of microbiologists dedicated to ‘scientifically exploring’ the oceans and space in search of forms of microbes adapted to extreme conditions. Indeed, these as-yet-unknown species could solve major societal challenges such as climate change, coral bleaching, or interplanetary survival.
CARBON 1 in the Aeolian Islands started from the very hypothesis that the places on Earth with the highest CO2 could harbor the organisms best suited to consume it. In fact, the Aeolian cyanobacterium that impressed the team has unique characteristics, including an astonishing rate of CO2 utilization.
Developments in the 2 Frontiers Projects
The research conducted by the 2FP developed with a second expedition, CARBON 2 in the hot springs of the Rocky Mountains in Colorado, USA, where CO2 levels are even higher.
CARBON 2 results are currently being analyzed but there is strong hope that, like the first expedition, other interesting life forms will be found.
In the meantime, all the information collected on the detected microorganisms will be published and made available to other scientists in the form of a database that matches DNA sequences to preserved bacterial samples.
The enzymes for CO2 fixation
The enzymes that enable these organisms to sequester and fix CO2 are mainly: ribulose 1,5-bisphosphate carboxylase/oxygenase (also called RuBisCO) and carbonic anhydrase (CA). Both enzymes are common in both archaeal and bacterial domains.
In addition to efficiently converting CO2 into biomass, some of these organisms can also convert it into useful compounds such as carbon monoxide, methane, methanol, or dimethyl ether (DME), olefins, and higher hydrocarbons that can contribute significantly to ecosystem protection.
Synthetic biology and enhancement of CO2 sequestration mechanism
The strong interest found in the enormous potential of these bacteria has recently led to the use of synthetic biology and protein and metabolic engineering to recreate new organisms capable of fixing CO2.
Indeed, synthetic biology succeeds in redesigning and repositioning innate metabolic pathways for CO2 fixation, modifying them to develop and optimize the efficiency and durability of CO2-fixing enzymes.
Engineered Escherichia coli
Among the first prokaryotic bacteria to be biologically engineered is E. coli. For example, in 2019, in a study published in Cell (3), researchers at the Weizmann Institute of Science in Israel had reported that they had developed a strain of the bacterium Escherichia coli that can consume CO2 to derive energy rather than use organic compounds such as sugars and fats.
On the other hand, the result was neither satisfactory nor industrializable, in particular, due to the fact that the engineered bacterium emitted more CO2 than it absorbed.
Other prokaryotes of interest
Other studies have also shown an interesting plasticity of carbon metabolism in carbon-fixing bacteria, including Synechococcus elongatus. (4)
Other engineered bacteria In order to implement their CO2 fixation capacity are Ralstonia eutropha (5), which in the presence of O2 is able to synthesize biomass, fuels, or chemical compounds from lower concentrations of CO2 and Rhodopseudomonas palustris (6) which showed a reduction in CO2 to methane. Sporomusa ovata (7) finally showed a high rate of solar-driven CO2 reduction and fixation with conversion to acetate.
Conclusions and perspectives
The hoped-for prospect is that these innovations will be able to find applications for CO2 sequestration and fixation in parallel with and in support of the ongoing energy transition.
In addition to bacterial engineering, recent advances are also focusing on biotechnological improvement of cyanobacteria and microalgae cultivation through photobioreactors (PBRs) as a sustainable alternative to reduce production costs on an industrial scale. (8)
Giulia Pietrollini
Notes
(1) Dario Dongo and Giulia Pietrollini. Algae and microalgae. Carbon farming and CO2 upcycling. FT (Food Times).
(2) Two Frontiers Project. Official website. https://twofrontiers.org/expeditions/carbon1
(3) Gleizer S, Ben-Nissan R, Bar-On YM, et al. Conversion of Escherichia coli to Generate All Biomass Carbon from CO2. Cell. 2019 Nov 27;179(6):1255-1263.e12. doi: 10.1016/j.cell.2019.11.009
(4) Kanno M, Carroll AL, Atsumi S. Global metabolic rewiring for improved CO2 fixation and chemical production in cyanobacteria. Nat Commun. 2017;8(1):1-11. doi: 10.1038/ncomms14724
(5) Liu C, Colón BC, Ziesack M, Silver PA, Nocera DG. Water splitting-biosynthetic system with CO2 reduction efficiencies exceeding photosynthesis. Science. 2016;352(6290):1210–1213. doi: 10.1126/science. aaf5039
(6) Fixen KR, Zheng Y, Harris DF, et al. Light-driven carbon dioxide reduction to methane by nitrogenase in a photosynthetic bacterium. Proc Natl Acad Sci. 2016;113(36):10163–10167. doi: 10.1073/pnas.1611043113
(7) Su Y, Cestellos-Blanco S, Kim JM, et al. Close-packed nanowire-bacteria hybrids for efficient solar-driven CO2 fixation. Joule. 2020;4(4):800-811. doi: 10.1016/j.joule.2020.03.001
(8) Cheng J, Zhu Y, Zhang Z, Yang W. Modification and improvement of microalgae strains for strengthening CO2 fixation from coal-fired flue gas in power plants. Biores Technol. 2019; 291:121850. doi: 10.1016/j.biortech.2019.121850
Graduated in industrial biotechnology and passionate about sustainable development.
