Mechanisms for Electrical Communication in Methane-Producing Microbial Communities
Abstract
It has recently been discovered that communities of archaea and bacteria can communicate via direct electrical connections that permit rapid exchange of electrons between species. For example, this direct interspecies electron transfer (DIET) is important in some anaerobic digesters in which bacteria and methanogens cooperate to convert organic wastes to methane. This is an important large-scale bioenergy strategy. DIET also takes place in terrestrial wetlands that are substantial sources of atmospheric methane. Studies with Geobacter species have provided a model for how bacteria can function as the electron-donating partner in DIET, connecting with methanogens via electrically conductive pili. However, there in no information on how archaea, such as methanogens make electrical connections with other cells. The electron transport proteins that are important for DIET in bacteria are not present in methanogens. Therefore, the objective of these studies is to determine the components of the electron transport pathway that permit the methanogen Methanosarcina barkeri to accept electrons via DIET for the reduction of carbon dioxide to methane. M. barkeri will be the focus of t hese studies because: 1) Methanosarcina species and close relatives are important methanogens in many environments; 2) M. barkeri is known to accept electrons via DIET; 3) M. barkeri can readily be cultivated in the laboratory under a diversity of conditions, including accepting electrons via DIET; 4) preliminary studies have demonstrated that M. barkeri increases expression of genes for putative outer-surface redox-active proteins when receiving electrons via DIET; and 5) M. barkeri can be genetically manipulated making it feasible to evaluate gene function through genetic analysis. The following hypotheses will be investigated: 1) identifying mutations that arise in M. barkeri during adaptive evolution of M. barkeri to grow via DIET will identify key electron transport systems involved in DIET; 2) comparison of the transcriptome of M. barkeri growing via DIET versus other growth conditions will reveal genes that encode proteins that are essential for DIET; 3) one or more of the genes previously found to encode outer surface proteins in M. barkeri are essential for DIET; 4) proteins that are essential and specific for DIET are closely associated and primarily localized in the membrane and outer surface of M. barkeri. These hypotheses will be investigated with genome resequencing and whole genome transcriptome approaches that we previously successfully employed in elucidating mechanisms for DIET in Geobacter species. Genes that are identified as having a potential role in DIET will be deleted from M. barkeri and the impact on DIET determined. The proteins encoded by genes that are essential for DIET will be localized in immunogold labeling. Thus, these studies will identify key steps in electron transfer into M. barkeri during DIET and the physical association of the proteins involved in DIET. The results are expected to have broad significance and application because M. barkeri and close relatives are major constituents of DIET-based microbial communities that play an important role in the anaerobic production and consumption of methane in a diversity of environments. The improved understanding of the electrification of microbial communities that will be developed will also aid in the design and optimization of synthetic microbial communities for applications in bioenergy and the sustainable production of biocommodities.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 07, 2018
- Source ID
- W911NF1710345
Entities
People
- Derek R. Lovley
Organizations
- Army Contracting Command
- United States Army
- University of Massachusetts Amherst