Characterization of guanidine carboxylases.

Area of Science:

• Microbiology
• Biochemistry
• Environmental Science

Background:

• Guanidine metabolism was considered a minor part of the nitrogen cycle.
• Bacterial RNA sensors (riboswitches) binding guanidine suggested a role in detoxification.
• Observed genetic organization implied potential guanidine import and assimilation.

Purpose of the Study:

• To investigate if bacteria can actively import and assimilate guanidine for nitrogen.
• To identify bacteria capable of utilizing guanidine as a sole nitrogen source.
• To characterize the enzymes involved in guanidine assimilation and degradation.

Main Methods:

• Isolation and cultivation of guanidine-assimilating bacteria.
• Proteome analysis to identify upregulated proteins in the presence of guanidine.
• Enzyme assays comparing guanidine carboxylase activity with urea carboxylase.

Main Results:

• Three enterobacteria (Raoultella terrigena, Erwinia rhapontici, Klebsiella michiganensis) were isolated for efficient guanidine utilization.
• Proteome analysis confirmed increased expression of carboxylase, hydrolases, and transporter genes with guanidine.
• Identified guanidine carboxylases showed substrate preference for guanidine over urea.

Conclusions:

• Certain bacteria actively import and assimilate guanidine, expanding the known nitrogen cycle pathways.
• The identified enzyme systems, including guanidine carboxylase, are crucial for guanidine assimilation.
• This research provides methods for isolating and analyzing guanidine-assimilating bacteria and their enzymes.