Light and carbon: Synthetic biology toward new cyanobacteria-based living biomaterials

Abstract

Cyanobacteria are ideal candidates to use in developing carbon neutral and carbon negative technologies; they are efficient photosynthesizers and amenable to genetic manipulation. Over the past two decades, researchers have demonstrated that cyanobacteria can make sustainable, useful biomaterials, many of which are engineered living materials. However, we are only beginning to see such technologies applied at an industrial scale. In this review, we explore the ways in which synthetic biology tools enable the development of cyanobacteria-based biomaterials. First we give an overview of the ecological and biogeochemical importance of cyanobacteria and the work that has been done using cyanobacteria to create biomaterials so far. This is followed by a discussion of commonly used cyanobacteria strains and synthetic biology tools that exist to engineer cyanobacteria. Then, three case studies-bioconcrete, biocomposites, and biophotovoltaics-are explored as potential applications of synthetic biology in cyanobacteria-based materials. Finally, challenges and future directions of cyanobacterial biomaterials are discussed.

Keywords: Biomaterials; Carbon sequestration; Cyanobacteria; Engineered living materials; Sustainability; Synthetic biology.

Graphical abstract

Fig. 1

Schematic illustration of synthetic biology tools that enable development of cyanobacteria-based biomaterials from lab prototypes to industry scale materials. Biomaterials illustrated (from left to right): Biocomposite of cyanobacteria grown on a loofah scaffold for enhanced CO₂ capture [25] could scale to become part of an industrial carbon capture system for scrubbing CO₂ from flue gas; Bioconcrete block made from biomineralizing cyanobacteria, sand, and gelatin [15] could scale to become a sustainable structural material that can “regrow”; a 3D printed microarray that captures current from photosynthesis of cyanobacteria colonies [26] could scale to become an efficient biophotovoltaic energy source.

Fig. 2

Transcription unit and plasmid types. (A) Diagram of a transcription unit, or segment of DNA that encodes a RNA molecule. The unit contains a promoter, ribosome-binding site, RNA-coding sequence, and a terminator. (B) A replicative plasmid has an origin of replication that enables its independent replication in the host cell. (C) An integrative plasmid has homology arms that promote homologous recombination with a targeted region on the host genome.

Fig. 3

Images and diagrams of three of existing cyanobacteria-based biomaterials: bioconcrete, a carbon capture biocomposite, and a biophotovoltaic. (A) Top: image of a bioconcrete block [15]. Bottom: diagram of internal structure of bioconcrete: cyanobacteria induced CaCO₃ precipitation and the crosslinking of the gelatin scaffold. (B) Top: image of a loofah scaffold for cyanobacteria carbon capture [25]. Bottom: diagram of internal structure of the biocomposite: cyanobacteria cells trapped on the loofah surface by a latex coating (C) Top: image of a 3D printed microarray biophotovoltaic device [26]. Bottom: diagram of flow of electrons starting from water oxidation due to cyanobacterial photosynthesis, electrons, then collected at the anode and transferred to a cathode where oxygen is reduced.

Fig. 4

Schematic of future directions of cyanobactera-based biomaterials: expanded genetic toolbox, intracellular biomaterials, and carbon cycle engineering (A) Expansion of the cyanobacteria engineering toolbox. Cyanophages mediate horizontal gene transfer in the ecosystem and could be used for delivering genetic payloads.Transposon mutagenesis introduces random insertions on the genome, leading to disruption or activation of neighboring genes. Recombineering uses phage-derived proteins, including single-stranded DNA annealing protein (SSAP), to enable targetable, multiplex genome editing. (B) Intracellular biomaterial engineering. Cyanbacterial gas vesicles can be extracted (or expressed in living cells) and used as contrast agents in MRI scans. Genes that form the cyanobacterial carboxysome can be inserted into plants to increase the photosynthetic efficiency. (C) Altering the global carbon cycle with cyanobacteria biomass sinking in the ocean: engineering cyanobacteria to increase ocean alkalinity and capture CO₂ as a CaCO₃ shell or other recalcitrant biopolymers would cause cells to sink in the water column, eventually becoming trapped in deep sea ocean sediments and sequestering the carbon.