Artificial cyanobacterial biofilm can sustain green ethylene production
for over a month

Date:
October 15, 2020
Source:
University of Turku
Summary:
Ethylene is one of the most important and widely used organic
chemicals.

A research group has designed a thin-layer artificial biofilm with
embedded cyanobacterial cell factories which were specifically
engineered for photosynthetic production of 'green' ethylene. The
fabricated biofilms have sustained ethylene production for up to
40 days.



FULL STORY ==========================================================================
The great global challenges of our time, including climate change, energy security and scarcity of natural resources, promote a transition from the linear fossil-based economy to the sustainable bio-based circular economy.

Taking this step requires further development of emerging technologies
for production of renewable fuels and chemicals.


========================================================================== Photosynthetic microorganisms, such as cyanobacteria and algae, show a
great potential for satisfying our demand for renewable chemicals and
reducing the global dependence on fossil fuels. These microorganisms
have the ability to utilise solar energy in converting CO2 into biomass
and a variety of different energy-rich organic compounds. Cyanobacteria
are also capable of holding novel synthetic production pathways that
allow them to function as living cell factories for the production of
targeted chemicals and fuels.

Ethylene is one of the most important organic commodity chemicals with
an annual global demand of more than 150 million tons. It is the main
building block in the production of plastics, fibres and other organic materials.

"In our research, we employed the genetically engineered cyanobacterium Synechocystis sp. PCC 6803 that expresses the ethylene-forming enzyme
(EFE) acquired from the plant pathogen, Pseudomonas syringae. The
presence of EFE in cyanobacterial cells enables them to produce
ethylene using solar energy and CO2 from air," says Associate Professor Allahverdiyeva-Rinne.

Ethylene has a high energy density that makes it an attractive fuel
source.

Currently, ethylene is produced via steam cracking of fossil
hydrocarbon feedstocks leading to a huge emission of CO2 into the
environment. Therefore, it is important to develop green approaches for synthesising ethylene.

"Although very promising results have been reported on ethylene-producing recombinant cyanobacteria, the overall efficiency of the available photoproduction systems is still very low for industrial applications. The ethylene productivity of engineered cyanobacteria is the most critical
variable for reducing the costs and improving efficiency," says
Postdoctoral Researcher Sindhujaa Vajravel.

However, cyanobacteria have several limitations for efficient production,
as they primarily accumulate biomass, not the desired products.

"They possess a giant photosynthetic light-harvesting antenna that leads
to self-shading and limited light distribution in suspension cultures,
which decreases productivity. The greatest limitation is that the
production period of the cells is short, only a few days," explains
Associate Professor Allahverdiyeva-Rinne.

To solve these two problems, researchers entrapped ethylene-producing cyanobacterial cells within thin-layer alginate polymer matrix. This
approach limits cell growth strongly, thus engaging efficient flux of photosynthetic metabolites for ethylene biosynthesis. It also improves
light utilisation under low-light conditions and strongly promotes
cell fitness. As a result, the artificial biofilms achieved sustainable photoproduction of ethylene for up to 40 days with a light-to-ethylene conversion efficiency that is 3.5 fold higher than in conventional
suspension cultures.

These findings open up new possibilities for the further development
of efficient solid-state photosynthetic cell factories for ethylene
production and scaling up the process to the industrial level.


========================================================================== Story Source: Materials provided by University_of_Turku. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Sindhujaa Vajravel, Sema Sirin, Sergey Kosourov, Yagut
Allahverdiyeva.

Towards sustainable ethylene production with cyanobacterial
artificial biofilms. Green Chemistry, 2020; 22 (19): 6404 DOI:
10.1039/D0GC01830A ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201015101801.htm

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