Investigating Nitrogen Fixation in a Photosynthetic Microbial Community


Photosynthetic microbial mats dominated by cyanobacteria achieve high rates of productivity using little more than sunlight, atmospheric gases (CO2 and N2), and trace nutrients. These complex, stratified ecosystems thus can provide experimentally tractable models to investigate functional properties of microbial communities and serve as valuable analogues for bioenergy production systems. The high rates of photosynthetic productivity observed in microbial mats are made possible by microbial nitrogen fixation, the process of converting N2 gas into biologically useful forms of nitrogen. Identifying which community members perform this process would provide a key to understanding overall community function. A team of investigators led by Lawrence Livermore National Laboratory scientists have reported new findings on nitrogen fixation in photosynthetic microbial mats using a combination of community gene expression analysis (metatranscriptomics), high-resolution microscopy, and nanoscale mass spectrometry (nanoSIMS). Metatranscriptomic analysis provided an overview of metabolically active community members capable of N2 fixation, thus providing an initial roster of target species worthy of further examination. Microscopically enabled nanoSIMS then provided the capability to narrow the search, tracking isotopically labeled nitrogen through the community at the scale of single cells. By coupling these two technologies, the team was able to identify specific members of the cyanobacterial portion of the community as the dominant N2 fixers and examine their spatial relationships within the overall community structure. These findings highlight the importance of pairing omics-driven techniques with complementary approaches that provide validation of functional predictions. By coupling cutting-edge experimental capabilities, researchers are developing a more sophisticated understanding of the biological rules that govern community structure and function, potentially enabling construction of analogous systems devoted to high-efficiency bioenergy production.


Woebken, D., L. C. Burow, F. Behnam, X. Mayali, A. Schintlmeister, E. D. Fleming, L. Prufert-Bebout, S. W. Singer, A. Lopez Cortes, T. M. Hoehler, J. Pett-Ridge, A. M. Spormann, M. Wagner, P. K. Weber, and B. M. Bebout. 2015. “Revisiting N2 Fixation in Guerrero Negro Intertidal Microbial Mats with a Functional Single-Cell Approach,” The ISME Journal 9, 485–96. DOI: 10.1038/ismej.2014.144.