Comparative analysis of cyanobacteria species reveals a novel guanidine-degrading enzyme that controls genomic stability of ethylene-producing strains

Abstract Recent studies have revealed the prevalence and biological significance of guanidine metabolism in nature. However, the metabolic pathways used by microbes to degrade guanidine or mitigate its toxicity have not been widely studied. Here we report a novel guanidine-degrading enzyme, Sll1077, identified in the model cyanobacterium Synechocystis sp. PCC 6803 through comparative proteomics and subsequent experimental validation. Although previously annotated as an agmatinase enzyme, Sll1077 is more likely a “guanidinase”, because it degrades guanidine rather than agmatine to urea. We demonstrate that the model cyanobacterium Synechococcus elongatus PCC 7942 strain engineered to express the bacterial ethylene-forming enzyme (EFE) exhibits 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 strain to achieve sustained high-level ethylene production. These findings expand our knowledge of natural guanidine degradation pathways and demonstrate their biotechnological application to support ethylene bioproduction.