Jay T. Lennon and Kathryn L. Cottingham. 2008. Microbial productivity in variable resource environments. Ecology 89:1001–1014.

Appendix B. Derivation of the bacterial growth efficiency (BGE) function and parameters.

Two comparative studies (del Giorgio and Cole 1998; Kritzberg et al 2005) have reported that BGE increases as a hyperbolic function of bacterial productivity (BP, mg·L^-1·h^-1):

BGE = BP/(BP+BR), where BR is bacterial respiration.

We rearranged this equation and used it to solve for BR:
            BR = (BP/BGE) – BP

With this information, we calculated bacterial consumption (BC = BP + BR) for each of the two data sets. This method for estimating BC has been used to represent the rate of DOC uptake by heterotrophic bacteria (del Giorgio and Davis 2003).

Next, we multiplied the estimated BC by 24 to get daily estimates (mg·L^-1·d^-1). We then re-plotted the predicted BGE as a function of BC. Finally, we fit the BGE-BC data to a Michaelis-Menten model: BGE = [BC*M_BGE]/[BC+K_BGE], where M_BGE is the maximum BGE and K_BGE is the BC that corresponds with one-half the M_BGE.

FIG. B1. The relationships between BGE and BC derived from del Giorgio and Cole (1998) and Kritzberg et al (2005). The lines represent predicted values generated from the Michaelis-Menten curve fitting (Sigma Plot, version 8.0).

TABLE B1. The parameter values (mean ± SEM) and their associated P values for the BGE and BC relationships derived from del Giorgio and Cole (1998) and Kritzberg et al (2005).

LITERATURE CITED

del Giorgio, P. A., and J. J. Cole. 1998. Bacterial growth efficiency in natural aquatic systems. Annual Review of Ecology and Systematics 29:503–541.

del Giorgio, P. A., and J. Davis. 2003. Patterns in dissolved organic matter lability and consumption across aquatic ecosystems. Pages 399–424 in S. E. Findlay and R. L. Sinsabaugh, editors. Aquatic ecosystems: interactivity of dissolved organic matter. Academic Press, New York, New York, USA.

Kritzberg, E. S., J. J. Cole, M. M. Pace, and W. Graneli. 2005. Does autochthonous primary production drive variability in bacterial metabolism and growth efficiency in lakes dominated by terrestrial C inputs? Aquatic Microbial Ecology 38:103–111.