Syringae Is Not Required for Stable Ethylene Production in Recombinant

Ethylene (C2H4) is a simple alkene of high commercial value due to multitude of large-scale uses in plastic industry, and as a potential fuel for spark-ignition piston engines. Currently ethylene is derived entirely from non-renewable sources, but it can also be produced directly from atmospheric CO2 via microbial biosynthesis in photosynthetic cyanobacterial hosts by the expression of ethylene forming enzyme (efe) from Pseudomonas syringae. One of the obstacles encountered in expression system design and optimization has been the instability of the efe gene in Synechocystis sp. PCC 6803 and Synechoccocus elongatus PCC 7942, which has previously been overcome by sequence optimization and altered expression strategies. This study focuses on understanding ethylene expression system stability in Synechocystis sp. PCC 6603, and demonstrates that gene optimization and removal of sequence elements implicated with gene inactivation are not essential for sustained production. The results suggest that the observed loss of production efficiency is more likely associated with other factors such as the chromosomal integration site or homologous sequence elements within autonomously replicating expression plasmids, which are central considerations in the development of any future production platforms.