초록
<P>Ethylene is the most widely produced petrochemical feedstock globally. It is currently produced exclusively from fossil fuels, and its production is the largest CO<SUB>2</SUB>-emitting process in the chemical industry. In this study, we report on a photobiological process for sustained production of ethylene from CO<SUB>2</SUB>. The <I>efe</I> gene encoding an ethylene-forming enzyme from <I>Pseudomonas syringae pv. Phaseolicola</I> was previously expressed in cyanobacterial strains, but was not stable. We modified the gene sequence to enhance its stability, and expressed it in <I>Synechocystis</I> sp. PCC 6803, leading to continuous ethylene production. The same ethylene production rate was sustained across four successive sub-cultures without apparent loss of ethylene-forming ability. Up to 5.5% of the fixed carbon was directed to ethylene synthesis, surpassing the published carbon-partition rate into the TCA cycle. Nitrogen- and phosphorus-enriched seawater can support both growth and ethylene production. Factors limiting ethylene production, including <I>efe</I> expression levels, light intensity and nutrient status, were identified and alleviated, resulting in a peak production rate of 5650 μL L<SUP>−1</SUP> h<SUP>−1</SUP> (7125 μg L<SUP>−1</SUP> h<SUP>−1</SUP>, 252 μmol L<SUP>−1</SUP> h<SUP>−1</SUP>, or 171 mg L<SUP>−1</SUP> day<SUP>−1</SUP>), which is higher than that reported for other algae biofuels and chemicals. This study suggests that <I>Synechocystis</I>, expressing the modified <I>efe</I> gene, has potential to be an efficient biological catalyst for the uptake and conversion of CO<SUB>2</SUB> to ethylene.</P><BR><BR><P>Graphic Abstract</P><P>The cyanobacterium <I>Synechocystis</I> PCC 6803 was engineered to produce high levels of ethylene from CO<SUB>2</SUB> by expressing the ethylene forming enzyme (EFE) from <I>Pseudomonas syringae</I>.<BR><IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2ee22555g'><BR></P>