COTNER, J.B.*; MAKINO, W.; HALL, E.K.; Univ. Minnesota- Twin Cities; Kyoto University; Univ. Minnesota- Twin Cities: Biological stoichiometry: From bacteria to ecosystems to global change

The growth rate of an organism has been described as a master variable that regulates intra-organismal and intra-cellular processes, but it is also responsive to environmental cues. Therefore, much of the work in our IRCEB project has focused on the effects of growth rate on the biochemical composition of Escherichia coli K-12, a model organism for prokaryotes, and multiple-species prokaryotic communities in freshwater lakes and the ocean. Varying growth (dilution) rates in phosphorus-limited chemostats had a strong effect on E. coli biochemical composition, with the most phosphorus (P)-rich (lowest carbon to phosphorus [C:P] ratio) organisms observed at the highest growth rates. Medium C:P had little effect on biomass C:P, indicating that this strain was strongly homeostatic. Examination of the literature suggests that multi-species bacterial communities are less homeostatic than individual strains, suggesting that increasing C:P nutrient supply ratios may select for high C:P strains in nature. Furthermore, increased temperatures generated increased bacterial C:P ratios both in cultures and in samples collected from several lakes and the ocean. These latter two results show that there are important feedbacks between the environment and bacterial community composition and biogeochemistry, which have important implications for regional and global nutrient and carbon cycles.