Do expected evolutionary trade-offs in enzyme activities manifest at the level of microbial community function?

Enzymes are proteins that catalyze (i.e. increase the rates of) chemical reactions. There are many different enzymes in the cells of all living things. And in all living things, including animals, plants and bacteria, there are enzymes that catalyze the process of respiration. This process takes complex organic compounds, such as sugars and fats, and breaks them into simpler forms to create energy. A by-product of respiration is carbon dioxide. For many organisms, the speed at which respiration occurs, and hence at which carbon dioxide is produced, increases as temperature increases. For this reason there is concern that bacteria and fungi in soils, where much of the world’s carbon is stored, will consume more soil carbon and respire more carbon dioxide to the atmosphere under global warming. If this occurs it may result in more rapid warming of the planet. There is much uncertainty as to whether this positive feedback to global warming will happen - in part because living things can produce different types of respiratory enzymes as temperatures change and not all enzymes may be similarly responsive to changing temperatures. As it gets warmer, they may produce enzymes that reduce respiration rates and cause the planet to warm more slowly than some predictions suggest. 

 

All samples and incubations for this work are complete.  Data are currently being analyzed and written up.
Collaborators:  Mark Bradford (Yale University)Noah Fierer (Univ. of Colorado-Boulder)

 

Associated Manuscripts:
Smets, W., J.W. Leff, M.A. Bradford, R.L. McCulley, S. Lebeer, N. Fierer. 2016. A method for simultaneous measurement of soil bacterial abundances and community composition via 16S rRNA gene sequencing. Soil Biology & Biochemistry. 96: 145-151.
Strickland, M.S., R.L. McCulley, J.A. Nelson, and M.A. Bradford. 2015. Compositional differences in root exudates elicit a limited functional and compositional response in soil microbial communities. Frontiers in Microbiology 6:817. doi: 10.3389/fmicb.2015.00817
Crowther, T., D. Maynard, J. Leff, E. Oldfield, R.L. McCulley, N. Fierer, M. Bradford. 2014. Predicting the responsiveness of soil biodiversity to deforestation: a cross-biome study. Global Change Biology 20(9):2983-2994. doi: 10.111/gcb.12565
Please contact Rebecca for copies. 

 

 

 Conceptual diagram of aggregate respiration rates of cold- (black hatched line) and warm-adapted (black solid line) microbial communities. Shown underneath each curve are a family of isoenzymes, which might be expressed by the same or different species but which have different thermal sensitivities.

Conceptual diagram of aggregate respiration rates of cold- (black hatched line) and warm-adapted (black solid line) microbial communities. Shown underneath each curve are a family of isoenzymes, which might be expressed by the same or different species but which have different thermal sensitivities.

This project tests whether bacteria and fungi in soils maintain initial increases in respiration rates when temperatures rise, or whether over time they decrease respiration rates in a way that is consistent with a change in the production of enzymes to those that slow respiration. To look at the bacteria and fungi in soils, the project will use DNA-sequencing and fatty-acid profiling methodologies. To determine respiration rates, carbon dioxide production from the soils will be measured using gas-analysis techniques. To generate differences in temperatures to which bacteria and fungi have been exposed, soils will be collected across a gradient from the arctic to the tropics, in winter and in summer, and also incubated in the laboratory at different temperatures.