Only very limited information is available regarding engineered
cyanobacteria with increased CO2-fixation and/or product formation.
The genes encoding the large and small subunits of RuBisCO, under the
control of the lac promoter (E. coli), have been introduced into the cyanobacterium
A. nidulans. Higher activity was detected in vitro in the
transformant cells compared to in the wild-type, probably because
more RuBisCO protein was expressed in the transformed cells.
Atsumi et al., (2009) successfully introduced the capacity to produce
isobutyraldehyde in cells of Synechococcus elongatus PCC 7942. By
additionally overexpressing RuBisCO the production of isobutyraldehyde
increased, demonstrating that RuBisCo/CO2-fixation is one of the bottlenecks
in the production of e.g. carbon based solar fuels in genetically
engineered photosynthetic cyanobacteria. By overexpressing genes
encoding selected enzymes in the pathway from the product of RuBisCo
activity to pyruvate, an increased specific rate of carbon fixation as well
as level of product (2,3-butandiol) formation in the engineered cells of
the cyanobacterium S. elongatus PCC 7942 were observed. In addition,
the insertion of a gene which allows the export sucrose in cells of
the cyanobacterium S. elongatus resulted in enhanced biomass production,
photosystem II activity, chlorophyll content and carbon fixation
. The increase of carbon fixation may be due to sucrose being a carbon
based sugar, and the engineered cells need more carbon fixation in order
supply carbon to the main metabolism as well as to produce the exported
sugar . A synthetic pathway based on the 3-hydroxypropionate bicycle
was created in order to re-assimilate glyoxylate, one of the products of
268 C. Durall, P. Lindblad / Algal Research 11 (2015) 263–270
the photorespiration process. The pathway was introduced into the cyanobacterium
S. elongatus PCC 7942 in order to bypass the photorespiration
process. The bypass may lead to the cells avoiding the loss of
carbon and nitrogen during the photorespiration process and thereby increase
the carbon fixation process