Widespread bacterial utilization of guanidine as nitrogen source

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Guanidine is sensed by bacterial riboswitches, primarily linked to Gdx transporters for export.
• Existing knowledge suggests riboswitches control guanidine detoxification, with limited understanding of its physiological roles.

Purpose of the Study:

• To investigate the physiological roles of guanidine in bacteria beyond detoxification.
• To explore the function of guanidine-riboswitch-controlled operons, including ABC transporters and carboxylases.

Main Methods:

• Isolation and characterization of enterobacteria utilizing guanidine as a nitrogen source.
• Proteome analysis to assess gene expression under guanidine induction.
• Enzyme assays to determine substrate specificity of urea/guanidine carboxylases.
• Metagenomic data analysis to map the distribution of relevant genes in bacterial habitats.

Main Results:

• Identified enterobacteria efficiently utilizing guanidine as a sole nitrogen source.
• Demonstrated that guanidine-inducible operons include importers, challenging the detoxification-only model.
• Showed that the carboxylase pathway enables guanidine assimilation.
• Characterized a guanidine-specific riboswitch-controlled carboxylase in *Erwinia rhapontici*.

Conclusions:

• Bacterial guanidine riboswitches control both uptake and assimilation of guanidine as a nitrogen source.
• This represents a paradigm shift from guanidine detoxification to its utilization.
• Guanidine is an important nitrogen source for certain bacteria, with widespread implications in various habitats.