Diffusion‐based process for carbon dioxide uptake and isoprene emission in gaseous/aqueous two‐phase photobioreactors by photosynthetic microorganisms

Abstract

Photosynthesis for the generation of fuels and chemicals from cyanobacteria and microalgae offers the promise of a single host organism acting both as photocatalyst and processor, performing sunlight absorption and utilization, as well as CO(2) assimilation and conversion into product. However, there is a need to develop methods for generating, sequestering, and trapping such bio-products in an efficient and cost-effective manner that is suitable for industrial scale-up and exploitation. A sealed gaseous/aqueous two-phase photobioreactor was designed and applied for the photosynthetic generation of volatile isoprene (C(5)H(8)) hydrocarbons, which operates on the principle of spontaneous diffusion of CO(2) from the gaseous headspace into the microalgal or cyanobacterial-containing aqueous phase, followed by photosynthetic CO(2) assimilation and isoprene production by the transgenic microorganisms. Volatile isoprene hydrocarbons were emitted from the aqueous phase and were sequestered into the gaseous headspace. Periodic replacement (flushing) of the isoprene (C(5)H(8)) and oxygen (O(2)) content of the gaseous headspace with CO(2) allowed for the simultaneous harvesting of the photoproducts and replenishment of the CO(2) supply in the gaseous headspace. Reduction in practice of the gaseous/aqueous two-phase photobioreactor is offered in this work with a fed-batch and a semi-continuous culturing system using Synechocystis sp. PCC 6803 heterologously expressing the Pueraria montana (kudzu) isoprene synthase (IspS) gene. Constitutive isoprene production was observed over 192 h of experimentation, coupled with cyanobacterial biomass accumulation. The diffusion-based process in gaseous/aqueous two-phase photobioreactors has the potential to be applied to other high-value photosynthetically derived volatile molecules, emanating from a variety of photosynthetic microorganisms.

Cyanobacterial cellulose synthesis in the light of the photanol concept

“…However, the requirements for the maintenance of a proper gas atmosphere in mass cultures of cyanobacteria for solar biofuel production -in other words a high level of carbon dioxide in order to avoid photorespiration and preventing super-saturation of oxygen -makes it difficult to recover volatile products. Nevertheless, there is hope that newly developed methods will circumvent these problems and optimize product recovery and cultivation conditions (Bentley and Melis, 2012).…”

Isoprene Production Via the Mevalonic Acid Pathway in Escherichia coli (Bacteria)

“…This could entail photosynthetic microorganisms [16,17] or processes based on bacterial fermentation of organic carbon substrates [18,19]. In contrast to isoprene production by plants, microbial systems are advantageous as they are cultivated in bioreactors making containment and sequestration of the volatile isoprene relatively easy.…”

Solar-to-fuel conversion in algae and cyanobacteria

“…Signifi cant in this development is the quantitative and spontaneous separation of isoprene from the biomass and the liquid culture that generates it. In particular, isoprene is collected from the headspace of the sealed photobioreactor (Bentley and Melis 2012 ). Production of the monoterpenes, β-phellandrene and limonene, and the sesquiterpene α-bisabolene has also been achieved by heterologous expression of plant genes.…”