Scalable Cultivation of Engineered Cyanobacteria for Squalene Production from Industrial Flue Gas in a Closed Photobioreactor

Abstract

Economically feasible photosynthetic cultivation of microalgal and cyanobacterial strains is crucial for the biological conversion of CO2 and potential CO2 mitigation to challenge global warming. To overcome the economic barriers, the production of value-added chemicals was desired by compensating for the overall processing cost. Here, we engineered cyanobacteria for photosynthetic squalene production and cultivated them in a scalable photobioreactor using industrial flue gas. First, an inducer-free gene expression system was developed for the cyanobacteria to lower production const. Then, the recombinant cyanobacteria were cultivated in a closed photobioreactor (100 L) using flue gas (5% CO2) as the sole carbon source under natural sunlight as the only energy source. Seasonal light intensities and temperatures were analyzed along with cyanobacterial cell growth and squalene production in August and October 2019. As a result, the effective irradiation hours were the most critical factor for the large-scale cultivation of cyanobacteria. Thus, an automated photobioprocess system will be developed based on the regional light sources.

Biocontainment of Engineered Synechococcus elongatus PCC 7942 for Photosynthetic Production of α-Farnesene from CO2

“…Previously, we performed scalable cultivation of engineered cyanobacteria in a closed photobioreactor using industrial flue gas (3−6% CO 2 ) in a natural gas power plant. 2 Outdoor cultivation of microalgae has also been performed using flue gas in coal-fired power plants (10−15% CO 2 ). 25 Thus, 5% CO 2 and 10% CO 2 were selected as high CO 2 concentrations conditions and potential CO 2 carbon sources for biomass and value-added chemical productions in the industry.…”

“…As engineering of the closed photo-bioprocess near a CO 2 -emitting plant (usually highly concentrated) is crucial for economically feasible CO 2 conversion, cyanobacterial strains should be genetically redesigned to adapt to the plant environment. Previously, we performed scalable cultivation of engineered cyanobacteria in a closed photobioreactor using industrial flue gas (3–6% CO 2 ) in a natural gas power plant . Outdoor cultivation of microalgae has also been performed using flue gas in coal-fired power plants (10–15% CO 2 ) .…”

“…The recent development of bio-solar cell factories that convert CO 2 to value-added chemicals using metabolic engineering of cyanobacteria has directed attention to the engineering of the photobioprocesses. − Although the current bottleneck in the valorization of CO 2 is low titers and productivities of the biochemicals used in food, medicine, cosmetics, and animal nutrition, national regulatory agencies, including the Environmental Protection Agency (US) and Ministry of Environment LMO Risk assessment Institute (Rep. of Korea), request for applications of genetically modified organisms (GMOs) because large-scale cultivations using engineered cyanobacteria increase the risk of escape and transfer of the synthetic genetic elements to the natural surroundings. To control the GMOs in biocontainment, synthetic genetic elements must have the following key features: (i) a robust genetic system to prevent the survivors, (ii) a stable genetic system for long-term applications, and (iii) no metabolic burden on engineered hosts …”

Engineering plant family TPS into cyanobacterial host for terpenoids production

“…FPPS engineered strains rendered a 12-fold and 50,000-fold increase in amorphadiene and squalene production, respectively (with MEP pathway genes, DXS, DXR, and IDI). A nearly similar strain with some further modifications was cultivated in a photobioreactor utilizing industrial flue gas as a carbon source for the generation of squalene (Choi et al 2020 ). Evolutionary engineering of PCC 7942 by optimizing RBS (with the help of RBS calculator) of farnesene synthase increased farnesene synthesis by two-fold (Pattharaprachayakul et al 2019 ).…”

Light-induced production of isobutanol and 3-methyl-1-butanol by metabolically engineered cyanobacteria

“…For most of these production systems, chemical-inducible promoters, such as an isopropyl-βd-thiogalactopyranoside (IPTG)-inducible promoter, are used to induce the expression of target genes [10]. However, IPTG is not an ideal inducer for scale-up because of its high operational cost [11,12]. Metalinducible promoters are also used for this process; however, the use of such promoters restricts the efficient recycling of water, thereby increasing the burden on the environment.…”