Cyanobacteria as the ultimate photo-catalysts of the conversion of CO2 into chemical commodities and liquid fuel, driven by either sunlight or electricity“

Klaas J. Hellingwerf

Swammerdam Institute for Life Sciences

Starting points:

Electricity will become a/the major renewable energy source

Solar panels and wind turbines will be the primary producers

Fuel in liquid/solid form and chemical commodities will also be needed in 2050

Mankind urgently needs to “close” the carbon cycle

04/19/2023 EASAC Breakthrough Meeting - Stockholm 2

CO2 + H2O Cells + O2

(plants, bacteria)

fossil fuels

Earth’ surface

energy (animals, bacteria)

CH4

O2

Global Carbon Cycle

04/19/2023 EASAC Breakthrough Meeting - Stockholm 3

Relevant considerations for a solution:

‘Artificial leaves’ vs. natural photosynthesis Plant photosynthesis is rather inefficient

(theoretical max.: 6 %; in practice often << 1 % Solution should not create new problem (e.g. in

food supply) 4th-generation approach necessary

04/19/2023 EASAC Breakthrough Meeting - Stockholm 4

EASAC Breakthrough Meeting - Stockholm 504/19/2023

sugar

‘Photofermentation’

04/19/2023 EASAC Breakthrough Meeting - Stockholm 6

CO2

Ethylene

Photo-fermentativemetabolism:

Green: storage compounds

EASAC Breakthrough Meeting - Stockholm 7

The ‘cell factory’ concept:

adhII

H2O

CO2 Thylakoids

Calvin cycle2 NADPH

3 ATP

TCA cycle

Ethanol

hv

O2pdc

Heterologous Fermentation Pathway

Genome

04/19/2023

CO2 + H2O C2H6O + O2 (catalyst)

04/19/2023 EASAC Breakthrough Meeting - Stockholm 8

CO2

LDH

Lactic acid

LDH

Lactate Production:

9

EASAC Breakthrough Meeting - Stockholm

Sensitivity analysis of a solar-cell factory

04/19/2023 10

Angermayr & Hellingwerf (2013) J Phys Chem B. DOI: 10.1021/jp4013152

EASAC Breakthrough Meeting - Stockholm

EASAC Breakthrough Meeting - Stockholm 1104/19/2023

Ethanol production in strain SAA012

CH3CH2OH

% of CO2 into ethanol: 65%

We can engineer with base-pair precision We – and others – can make a wide range of

products Synechocystis is pluGbug for CO2

For selected products > 70 % carbon partitioning achievable

Wild type cyanobacteria have a photosynthetic efficiency of > 10 %

Approach does not compete with food supply; does not create a minerals problem and has a limited water requirement as compared to traditional crops

04/19/2023 EASAC Breakthrough Meeting - Stockholm 12

Pilot plant:

04/19/2023 EASAC Breakthrough Meeting - Stockholm 13

Assuming:

04/19/2023 EASAC Breakthrough Meeting - Stockholm 14

Efficiency of PV-cells: 50%Efficiency of LEDs: 70%Efficiency conversion 700 nm photons into fuel of 35%

Overall efficiency = 10%! => 0.1 MW/acre

In other words: A field full of solar panels on non-fertile soil would drive natural photosynthesis more efficiently than plant photosynthesis itself!

04/19/2023 EASAC Breakthrough Meeting - Stockholm 15

Design of 3-D LED-based solar reactorsfor value-added chemicals:

CO2 producer

Conclusions:

The ‘race is on’ for economic exploitation between artificial leaves and designer cyanobacteria.

Already - using modestly modified cyanobacteria - the living organisms have taken the lead

04/19/2023 EASAC Breakthrough Meeting - Stockholm 16

CO2

intermediate product

cel polymers

organel

living cel or plant

hydrolysis

product

heat

heat

investedenergy

conserved energy

waste

fermentation

energy

04/19/2023 EASAC Breakthrough Meeting - Stockholm 17

CO2

intermediair product productinvestedenergy

conserved energy

Cell factory for ‘photofermentation’

04/19/2023 EASAC Breakthrough Meeting - Stockholm 18

04/19/2023 EASAC Breakthrough Meeting - Stockholm 19

A Synthetic Systems Biology approach:

A~CO2B

DE

A

E

Promoter

biofuelproduct

NH4

+

GAP

Ammonia availability is often used as a control parameter to regulate biomass formation

CO2

cells

Cassette

4 mmol/gdw/h

(V > 4 mmol/gdw/h!)

a

b

Challenge: make b/a > 1!!

EASAC Breakthrough Meeting - Stockholm 2004/19/2023

pluGbug for CO2

04/19/2023 EASAC Breakthrough Meeting - Stockholm 21

the pluGbugconcept