Presented herein are Synechococcus strains engineered to express the bacterial ethylene-forming enzyme (EFE) that exhibit unstable ethylene production due to toxicity and genomic instability induced by accumulation of the EFE-byproduct guanidine. Co-expression of EFE and Sll1077 significantly enhanced genomic stability and enabled the resulting Synechococcus strain GD-EFE7942 to achieve sustained high-level ethylene production. The engineered strains and methods disclosed herein are useful for guanidine degradation pathways and for ethylene bioproduction in cyanobacteria.

Methods and microorganisms are genetically engineered to continuously produce ethylene by microbial fermentation, particularly by the microbial fermentation of a gaseous substrate. The microorganisms are C1-fixing. Further, the gaseous substrate comprises CO.sub.2 and an energy source. The production of ethylene can be improved by varying promoters or nutrient limiting means.

Presented herein are Synechococcus strains engineered to express the bacterial ethylene-forming enzyme (EFE) that exhibit unstable ethylene production due to toxicity and genomic instability induced by accumulation of the EFE-byproduct guanidine. Co-expression of EFE and Sll1077 significantly enhanced genomic stability and enabled the resulting Synechococcus strain GD-EFE7942 to achieve sustained high-level ethylene production. The engineered strains and methods disclosed herein are useful for guanidine degradation pathways and for ethylene bioproduction in cyanobacteria.