A system for growing Geobacter sulfurreducens under anaerobic conditions in 
chemostats was developed in order to study the physiology of this organism under 
conditions that might more closely approximate those found in the subsurface 
than batch cultures. Geobacter sulfurreducens could be cultured under 
acetate-limiting conditions with fumarate or Fe(III)-citrate as the electron 
acceptor at growth rates between 0.04 and 0.09 h(-1). The molar growth yield was 
threefold higher with fumarate as the electron acceptor than with Fe(III), 
despite the lower mid-point potential of the fumarate/succinate redox couple. 
When growth was limited by availability of fumarate, high steady-state 
concentrations were detected, suggesting that fumarate is unlikely to be an 
important electron acceptor in sedimentary environments. The half-saturation 
constant, Ks, for acetate in Fe(III)-grown cultures (10 microM) suggested that 
the growth of Geobacter species is likely to be acetate limited in most 
subsurface sediments, but that when millimolar quantities of acetate are added 
to the subsurface in order to promote the growth of Geobacter for bioremediation 
applications, this should be enough to overcome any acetate limitations. When 
the availability of electron acceptors, rather than acetate, limited growth, G. 
sulfurreducens was less efficient in incorporating acetate into biomass but had 
higher respiration rates, a desirable physiological characteristic when adding 
acetate to stimulate the activity of Geobacter species during in situ uranium 
bioremediation. These results demonstrate that the ability to study the growth 
of G. sulfurreducens under steady-state conditions can provide insights into its 
physiological characteristics that have relevance for its activity in a 
diversity of sedimentary environments.