A guanidine-degrading enzyme controls genomic stability of ethylene-producing cyanobacteria

Bo Wang,Yao Xu,Carl H Johnson,Joshua S Yuan,Xin Wang,Jamey D Young,Jianping Yu

doi:10.1038/s41467-021-25369-x

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, via comparative proteomics and subsequent experimental validation, we demonstrate that Sll1077, previously annotated as an agmatinase enzyme in the model cyanobacterium Synechocystis sp. PCC 6803, is more likely a guanidinase as it can break down guanidine rather than agmatine into urea and ammonium. 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 enhances genomic stability and enables 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.

Highlights

Recent studies have revealed the prevalence and biological significance of guanidine metabolism in nature
It was reported that a wide range of microorganisms possesses a class of guanidine riboswitches that control the expression of downstream genes, a majority of which encode proteins involved in nitrogen metabolism, nitrate/sulfate/ bicarbonate transport, and guanidine export[5,8,9,10,11,12]
Given that the impacts of guanidine on microorganisms are unclear, we studied guanidine degradability and toxicity in two model cyanobacterial species: Synechocystis 6803 and Synechococcus 7942

Summary

Introduction

Recent studies have revealed the prevalence and biological significance of guanidine metabolism in nature. Coexpression of EFE and Sll1077 significantly enhances genomic stability and enables 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. A previously annotated urea carboxylase was reported to carboxylate guanidine to form carboxyguanidine[5], which is degraded by a carboxyguanidine deiminase followed by further degradation by allophanate hydrolase[13] Another class of enzymes regulated by guanidine riboswitches are annotated as agmatinases in the arginase superfamily[5,9,14,15], which catalyze the breaking of C–N bonds in the guanidyl moiety of agmatine, releasing urea[16].

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Results

Conclusion