Evidence for nitrogen fixation by "Dehalococcoides ethenogenes" strain 195

Area of Science:

• Microbiology
• Environmental Science
• Biochemistry

Background:

• Dehalococcoides ethenogenes is a key microorganism in the reductive dechlorination of chlorinated ethenes.
• Previous genome annotation suggested the presence of a nitrogenase operon in strain 195.
• The role of nitrogen fixation in this organism under specific nutrient conditions was not fully understood.

Purpose of the Study:

• To investigate the nitrogen fixation capabilities of Dehalococcoides ethenogenes strain 195.
• To confirm if strain 195 can utilize atmospheric dinitrogen (N2) as a nitrogen source.
• To determine the conditions under which nitrogen fixation occurs in this bacterium.

Main Methods:

• Long-term microbial growth experiments were conducted.
• Gene expression analysis was performed to assess nitrogenase activity.
• (15)N(2)-isotope labeling experiments were utilized to track nitrogen assimilation.

Main Results:

• Dehalococcoides ethenogenes strain 195 demonstrated the ability to fix atmospheric dinitrogen.
• Nitrogen fixation was confirmed to occur when ammonium, a common fixed-nitrogen source, was unavailable.
• Evidence from growth, gene expression, and isotope measurements supports this finding.

Conclusions:

• Dehalococcoides ethenogenes strain 195 possesses a functional nitrogenase system enabling atmospheric nitrogen fixation.
• This metabolic capability is crucial for the organism's survival and growth in nitrogen-limited environments.
• The findings expand our understanding of the biogeochemical cycling of nitrogen mediated by dehalogenating bacteria.