Microbes

The microbial chassis used to produce L-lactate is a derivative of Synechocystis PCC 6803 wildtype maintained at the Molecular Microbial Physiology group at the University of Amsterdam. This cyanobacterium has the ability of directly fixing CO₂ using the energy of (sun)light via photosynthesis. We engineered it to be able to deviate carbon from pyruvate directly into L-lactate. This was achieved through the heterologous expression of a L-lactate dehydrogenase originally derived from the lactic acid bacterium Lactococcus lactis sp. cremoris. The resulting lactate-producing mutant of Synechocystis, strain SAA023, can deviate over 20% of the carbon it fixes towards lactate production while growing exponentially, and sustain a production rate over 6.2 mg.OD^-1.h^-1. In the ENGICOIN project, strain SAA023 is used at the ACEA site in a photobioreactor to sustainably convert the CO₂ produced there into the valuable compound L-lactate, which is used in the synthesis of polylactate bioplastics.

Cupriavidus necator H16 (formerly known as Ralstonia eutropha H16) is a hydrogen-oxidizing bacterium, with the ability to grow in presence and absence of oxygen. It can easily adapt to different lifestyles such as heterotrophic, feeding on organic compounds, and autotrophic, feeding with CO₂. Furthermore, C. necator is able to use hydrogen as a source of energy. When growing under autotrophic conditions, C. necator fixes carbon of CO₂ through the reductive pentose phosphate pathway. From biotechnological point of view, C. necator has demonstrated to be one of the best microorganisms to produce and sequester polyhydroxyalkanoate (PHA) plastics accumulating to levels around 90% of the cell's dry weight. Engicoin project proposes to use these abilities of C. necator to stablish a microbial factory capable to transform a contaminant, e.g. CO₂, in an added-value product, e.g. bioplastic, in a bioconversion process that can be achieved in a bioreactor.

Acetobacterium woodii is a species of gas-fermenting bacteria. It is capable of absorbing CO₂ from its environment and is known to produce organic acids such as acetate. A. woodii is an anaerobe, incapable of growth in the presence of oxygen. Species like A. woodii are typically found in anaerobic layers of soil or in marine sediments but have also been found in animal guts. A. woodii turns absorbed carbon into biomass and organic acids by feeding it into a metabolic pathway known as the Wood-Ljungdahl Pathway (WLP). Organisms that make use of the Wood-Ljungdahl Pathway (also known as acetogens) are important players in the global carbon cycle. Approximately 10¹² kg of acetate are produced per year by acetogens via the Wood-Ljungdahl Pathway.  

One goal of ENGICOIN is to harness the ability of these acetogenic bacteria to absorb CO₂. To increase the variety of chemical products that A. woodii can produce, a novel strain was created using genes from another anaerobic bacterium, Clostridium acetobutylicum. When inserted into A. woodii, these genes allow it to produce acetone, a valuable industrial chemical, from waste CO₂.