AbstractDetermining how microbial communities organize and function at the ecosystem level is essential to understanding and predicting how they will respond to environmental change. Mathematical models can be used to describe these communities, but properly representing all the biological interactions in extremely diverse natural microbial ecosystems in a mathematical model is challenging. We examine a complementary approach based on the maximum entropy production (MEP) principle, which proposes that systems with many degrees of freedom will likely organize to maximize the rate of free energy dissipation. In this study, we develop an MEP model to describe biogeochemistry observed in Siders Pond, a phosphate limited meromictic system located in Falmouth, MA that exhibits steep chemical gradients due to density-driven stratification that supports anaerobic photosynthesis as well as microbial communities that catalyze redox cycles involving O, N, S, Fe, and Mn. The MEP model uses a metabolic network to represent microbial redox reactions, where biomass allocation and reaction rates are determined by solving an optimization problem that maximizes entropy production over time, and a 1D vertical profile constrained by an advection-dispersion-reaction model. We introduce a new approach for modeling phototrophy and explicitly represent oxygenic photoautotrophs, photoheterotrophs and anoxygenic photoautotrophs. The metabolic network also includes reactions for aerobic organoheterotrophic bacteria, sulfate reducing bacteria, sulfide oxidizing bacteria and aerobic and anaerobic grazers. Model results were compared to observations of biogeochemical constituents collected over a 24 h period at 8 depths at a single 15 m deep station in Siders Pond. Maximizing entropy production over long (3 day) intervals produced results more similar to field observations than short (0.25 day) interval optimizations, which support the importance of temporal strategies for maximizing entropy production over time. Furthermore, we found that entropy production must be maximized locally instead of globally where energy potentials are degraded quickly by abiotic processes, such as light absorption by water. This combination of field observations and modeling results indicate that natural microbial systems can be modeled by using the maximum entropy production principle applied over time and space using many fewer parameters than conventional models.
|Project Title||Modeling how virus-microbe interactions influence carbon flow at a deep-sea volcano|
|Created||August 1, 2017|
|Modified||August 3, 2017|
In order to break open the black box of deep-sea hydrothermal vent microbiology and take our understanding of subseafloor microbial processes and the carbon cycle to a new level, we propose to investigate autotrophy in the rocky subseafloor using molecular biological, cultivation, and geochemical techniques at Axial Seamount, an active submarine volcano that will soon be part of a seafloor cabled observatory. In line with the Moore Foundation’s MMI objectives, this project will address the functional roles of various autotrophic subseafloor microbial community members across temperature and metabolism classifications; their relationships with each other, with viruses, and with other sources of syntrophic metabolic energy; and their collective impact on carbon biogeochemistry as dictated by environmental gradients in temperature and geochemistry. Of particular importance is the inclusion of seafloor experimentation at Axial, which will not only yield data on microbial activity and carbon transformations in situ, but will also set the stage for integration of a microbial instrument at the Axial cabled observatory. Our comprehensive suite of land-based, shipboard, and in situ analyses will yield cross-disciplinary advances in our understanding of the microbial ecology and geochemistry of carbon cycling in the subseafloor biosphere at mid-ocean ridges.
|Julie A. Huber||Woods Hole Oceanographic Institution (WHOI)||Lead Principle Investigator||✓|
|David A. Butterfield||National Oceanic and Atmospheric Administration (NOAA-PMEL)||Co-Principal Investigator|
|James F. Holden||University of Massachusetts Dartmouth (UMass Dartmouth)||Co-Principal Investigator|
|Jullie Zeigler Allen||J. Craig Venter Institute (JCVI)||Co-Principal Investigator|
|Joseph J. Vallino||Marine Biological Laboratory (MBL)||Co-Principal Investigator|