Ethylene is one of the most important building blocks in the petrochemical industry and a natural plant hormone widely used in agriculture. Traditional ethylene production mainly relies on the steam cracking of petroleum-based feedstock. Considering the energy crisis and environmental pollution, sustainable and eco-friendly strategies are urgent to be explored. Benefiting from a high photosynthetic efficiency, clear genomic information and facilitated genetic manipulation, cyanobacteria are particularly thought to be potential candidates for the direct bio-production of ethylene from carbon dioxide, driven by solar energy. 

Fig. 1 The schematic diagram for ethylene production in Synechocystis sp. PCC 6803. (Image by Metabolic Engineering Group, QIBEBT)

Researchers from the Metabolic Engineering Group at Qingdao Institute of Bioenergy and BioprocessTechnology (QIBEBT), Chinese Academy of Sciences (CAS), have recently made progress on the photosynthetic production of ethylene using model cyanobacterium Synechocystis sp. PCC6803. Continuous and stable ethylene production was achieved by introducing a codon-optimized ethylene-forming enzyme (EFE) from Pseudomonas syringae pv. sesami and using 2-oxoglutarate (2-OG) as the substrate. Based on diverse promoters screening, PcpcB was proven to be a highly efficient promoter for ethylene production in cyanobacteria. The genes encoding 2-OG decarboxylase (OGDC) and succinic semialdehyde dehydrogenase (SSADH) in the tricarboxylic acid (TCA) cycle in Synechocystis sp. PCC 6803 were identified, and the TCA cycle was genetically modified by blocking these two enzymes with the simultaneous overexpression of EFE.  

Meanwhile, a gene encoding 2-OG permease (KgtP) from E. coli was introduced into the phaAB loci to increase the 2-OG supply. A peak volumetric production rate of 9.7 mL L^-1 h^-1 for ethylene was eventually achieved in the Synechocystis recombinant, with the genetic modification of TCA cycle and heterologous expression of 2-oxoglutarate permease by the modified semi-continuous cultivation. 

This work was supported by the Excellent Youth Award of Shandong Natural Science Foundation. It had been published online in journal Green Chemistry entitled “Enhancing photosynthetic production of ethylene in genetically engineered Synechocystis sp. PCC 6803”. 

Link of the publication: http://pubs.rsc.org/en/content/articlelanding/2014/gc/c4gc01730g 

Contact: 

Prof. LU Xuefeng 
E-mail: lvxf (AT) qibebt.ac.cn  
Webpage: http://english.qibebt.cas.cn/rh/rs/bc/mee/