Transcriptomic and genetic analysis of direct interspecies electron transfer

Area of Science:

• Microbiology
• Environmental Science
• Molecular Biology

Background:

• Interspecies electron transfer (IET) is crucial for microbial community function.
• Distinguishing between direct interspecies electron transfer (DIET) and H2 interspecies transfer (HIT) is challenging.
• Understanding IET mechanisms is vital for various applications, including biotechnology and environmental remediation.

Purpose of the Study:

• To investigate if metatranscriptomic analysis can differentiate between DIET and HIT pathways.
• To compare gene expression profiles of Geobacter sulfurreducens when acting as an electron acceptor for DIET (Geobacter metallireducens) versus HIT (Pelobacter carbinolicus).

Main Methods:

• Coculture experiments with defined electron donor-acceptor pairs (G. metallireducens/G. sulfurreducens for DIET, P. carbinolicus/G. sulfurreducens for HIT).
• Metatranscriptomic analysis to quantify gene transcript abundance in cocultures.
• Analysis of specific genes related to electron uptake (hydrogenase), electron export (cytochromes, pili), and metabolism (acetate).
• Construction and testing of mutant strains of G. metallireducens lacking pili, flagella, or specific cytochromes.

Main Results:

• G. sulfurreducens showed significantly lower transcript abundance for uptake hydrogenase genes in DIET cocultures compared to HIT cocultures.
• Transcript abundance for OmcS, a pilus-associated cytochrome essential for DIET, was dramatically higher in DIET cocultures.
• Genes involved in pili and flagella biogenesis were highly expressed in G. metallireducens during DIET.
• Mutants of G. metallireducens deficient in pili, flagella, or cytochrome Gmet_2896 failed to form cocultures with G. sulfurreducens.
• Distinct gene expression patterns clearly differentiated DIET and HIT.

Conclusions:

• Metatranscriptomic analysis provides a powerful tool to distinguish between DIET and HIT in anaerobic microbial communities.
• Specific gene expression signatures, particularly involving electron transport components like pili and cytochromes, are indicative of DIET.
• The findings highlight the importance of cell surface structures and electron conduits in mediating DIET.
• This approach holds promise for elucidating IET mechanisms in more complex, uncultured microbial ecosystems.