Methanobacterium Capable of Direct Interspecies Electron Transfer

Area of Science:

• Microbiology
• Environmental Science
• Biochemistry

Background:

• Direct interspecies electron transfer (DIET) is a key process in microbial metabolism, particularly in anaerobic environments.
• Previously, DIET was thought to be limited to methanogens within the order Methanosarcinales.
• This led to the assumption that the presence of other methanogen groups, like Methanobacterium, indicated a lack of DIET.

Purpose of the Study:

• To investigate the potential for DIET in methanogens outside of the Methanosarcinales order.
• To determine if Methanobacterium species can engage in DIET with bacterial partners.
• To explore the conditions and mechanisms facilitating DIET in novel microbial consortia.

Main Methods:

• Culturing of a Methanobacterium strain (YSL) in defined cocultures with Geobacter metallireducens.
• Microscopic analysis of coculture aggregates to observe cell-to-cell associations.
• Assessing the role of granular activated carbon in promoting coculture formation.

Main Results:

• A strain of Methanobacterium (YSL) was demonstrated to grow via DIET with Geobacter metallireducens.
• Cocultures formed aggregates with uniform dispersion of both species, facilitating close physical contact.
• Geobacter metallireducens, even strains lacking conductive pili, could grow in coculture, indicating DIET is the primary mechanism.
• Granular activated carbon enhanced the initial formation of these DIET-based cocultures.

Conclusions:

• The capacity for DIET is more widespread among methanogens than previously assumed, extending beyond Methanosarcinales.
• The discovery of DIET in Methanobacterium challenges its historical role as an exemplar solely for H2-mediated interspecies electron transfer.
• Further research employing innovative microbial isolation and characterization techniques is crucial for understanding methanogenic community functions.