Effects of cultivation conditions on acid–base titration properties of Shewanella putrefaciens

Acid–base titrations were conducted on pure strain laboratory cultures of the Gram-negative, facultatively aerobic bacterium Shewanella putrefaciens, cultivated under a range of conditions. Bacteria used in acid–base titrations were cultivated for periods of 24 to 100 h (exponential growth phase to late stationary phase), in varying media compositions (rich to minimal), and under aerobic and anaerobic conditions. In addition, two mutant strains of S. putrefaciens were tested, which are respiration-deficient with respect to U(VI) and Fe(III). Titration data were used to constrain the abundances and proton-exchange properties of bacterial surface functional groups using a discrete multisite surface complexation model. Estimated properties for titratable functional groups at the bacteria–water interface were compared on the basis of cultivation conditions. Results demonstrate that the acid–base behavior of the S. putrefaciens surface is largely insensitive to variations in culture age and media composition, yielding values for a wide range of aerobic cultivation conditions that are not significantly different on a statistical basis. Conversely, results for anaerobic growth, in which Fe(III) was supplied as sole terminal electron acceptor, show significantly lower bacterial site densities and differing functional-group acid dissociation constants. It is recommended that different profiles for aerobic and anaerobic Gram-negative bacteria be used in aqueous speciation calculations involving a bacterial component.