Element content of Pseudomonas fluorescens varies with growth rate and temperature:: A replicated chemostat study addressing ecological stoichiometry

Ecological stoichiometry is emerging as a central organizing framework upon which our perceptions of aquatic trophic dynamics are being reshaped. The microbial component of aquatic systems is crucial to overall nutrient dynamics, yet little data are available addressing the ecological stoichiometry of microorganisms. Pseudomonas fluorescens, a commonly encountered bacterium, was used as a model organism to investigate the relationships among temperature, growth rate, and element stoichiometry. P. fluorescens was grown in chemostats at low dilution rates (ranging between 0.03 and 0.13 h(-1)) and realistic environmental temperatures (ranging between 14 degrees C and 28 degrees C). Cells accumulated elements as an interactive function of temperature and growth rate. The highest element concentrations corresponded to cells growing slowly under low temperatures and to cells growing rapidly under warm conditions. Additionally, small cells had higher concentrations of elements than did large cells. Element ratios (C : N, C: P, and N: P) varied more as a function of growth rate than of temperature. The same dissolved resource pool could conceivably yield bacteria of differing element content simply as an interactive function of growth rate and temperature.