期刊
BIOGEOCHEMISTRY
卷 121, 期 2, 页码 287-304出版社
SPRINGER
DOI: 10.1007/s10533-014-0030-y
关键词
Ecological stoichiometry; Extracellular enzymes; Enzyme kinetics; Microbial community; Microbial metabolism
资金
- NSF Ecosystem Sciences program [DEB-0918718]
- Sevilleta LTER Program
- NSF [DEB-0315686, DBI-0420965, DBI-0521018]
- Michigan Sea Grant College Program under NOAA [NA76RG0133]
- DOE BER Science Focus Area grant
- DOE BER [DE-SC0008088]
- Direct For Biological Sciences
- Division Of Environmental Biology [1232294] Funding Source: National Science Foundation
- U.S. Department of Energy (DOE) [DE-SC0008088] Funding Source: U.S. Department of Energy (DOE)
Microbial community metabolism relies on external digestion, mediated by extracellular enzymes that break down complex organic matter into molecules small enough for cells to assimilate. We analyzed the kinetics of 40 extracellular enzymes that mediate the degradation and assimilation of carbon, nitrogen and phosphorus by diverse aquatic and terrestrial microbial communities (1160 cases). Regression analyses were conducted by habitat (aquatic and terrestrial), enzyme class (hydrolases and oxidoreductases) and assay methodology (low affinity and high affinity substrates) to relate potential reaction rates to substrate availability. Across enzyme classes and habitats, the scaling relationships between apparent V-max and apparent K-m followed similar power laws with exponents of 0.44 to 0.67. These exponents, called elasticities, were not statistically distinct from a central value of 0.50, which occurs when the K-m of an enzyme equals substrate concentration, a condition optimal for maintenance of steady state. We also conducted an ecosystem scale analysis of ten extracellular hydrolase activities in relation to soil and sediment organic carbon (2,000-5,000 cases/enzyme) that yielded elasticities near 1.0 (0.9 +/- A 0.2, n = 36). At the metabolomic scale, the elasticity of extracellular enzymatic reactions is the proportionality constant that connects the C:N:P stoichiometries of organic matter and ecoenzymatic activities. At the ecosystem scale, the elasticity of extracellular enzymatic reactions shows that organic matter ultimately limits effective enzyme binding sites. Our findings suggest that one mechanism by which microbial communities maintain homeostasis is regulating extracellular enzyme expression to optimize the short-term responsiveness of substrate acquisition. The analyses also show that, like elemental stoichiometry, the fundamental attributes of enzymatic reactions can be extrapolated from biochemical to community and ecosystem scales.
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