Venn Diagram

Microbial Ecology

Understanding How Microbial Communities Work

What makes a microbial system stable or unstable with respect to function and community structure? For a long time, researchers hypothesized that stability is related to diversity with low and high diversity systems being less stable and medium diversity systems being more stable. As part of my post-doctoral work at MSU and Stanford, I studied the functional networks and community structures of dozens of anaerobic bioreactors as model systems under normal and perturbed conditions and proved that it is the flexibility of functional networks (i.e., the ability to process substrate in parallel) that makes a system more stable (Hashsham, et al., Fernandez et al., 2000). I demonstrated that, in this respect, complex biological systems are no different than transportation grids or computational networks. They all are more efficient and more stable when performing their corresponding "function" in parallel. My approach to compute the functional stability of microbial communities has been referenced numerous times and incorporated in reviews that discuss the impact of such studies in very broad terms. For example, Free and Barton refer to the above publications in the context of what makes the biosphere stable and self-regulatory (Do evolution and ecology need the Gaia hypothesis? Trends in Ecology and Evolution, 22(11): 2007). [The Gaia hypothesis treats the Earth as a single organism consisting of coupled biosphere and their physical components. This interest in quantitative microbial ecology has continued since then (Callister et al., 2009) and has received a renewed interest due to the relevance of ecological principles to the gut microbiome and other environmental systems (Johnson et al., 2016).

Selected Publicatons

  • Hashsham S., A. Fernandez, S. Dollhopf, F. Dazzo, R. Hickey, J. Tiedje, and C. Criddle. Parallel processing of substrate correlates with greater functional stability in methanogenic bioreactor communities perturbed by glucose. Applied and Environmental Microbiology. 66 (9):4050-4057, 2000.
  • Fernandez, A., S. Hashsham, S. Dollhopf, L. Raskin, O. Glagoleva, F. Dazzo, R. Hickey, C. Criddle, and J. Tiedje. Flexible community structure correlates with stable community function in methanogenic bioreactor communities perturbed by glucose. Applied and Environmental Microbiology. 66 (9):4058-4067, 2000.
  • Stephen J Callister, J Jacob Parnell, Michael E Pfrender, and Hashsham, Syed. Relating perturbation magnitude to temporal gene expression in biological systems, BMC Research Notes, 2:43. doi: 10.1186/1756-0500-2-43, 2009.
  • Johnson, T. A.; Stedtfeld, R. D.; Wang Qiong; Cole, J. R.; Hashsham, S. A.; Looft, T.; Zhu YongGuan; Tiedje, J. M. Clusters of antibiotic resistance genes enriched together stay together in swine agriculture. mBio. Vol 7 Issue: 2 Pages: e02214-e02214-15. 2016.