Characterization of Bacterial Exudates Through Potentiometric Titrations

Bacterial exudates are organic molecules released by bacteria that have proton- and metal-binding capacities, as well as the ability to facilitate redox reactions. However, the binding sites responsible for these functions are poorly characterized. In this work we examine the concentrations and types of proton active sites through potentiometric titrations of exudate solutions produced from several bacterial species. Additionally, we report the first measurement of sulfhydryl site concentrations of bacterial exudates. Finally, we examine the processes by which these exudates are produced in order to constrain the relative importance of active and passive production of the exudate molecules. Our results demonstrate that, while overall proton-binding behavior is primarily dependent on the amount of organic material produced, the concentration of sulfhydryl sites present on the exudate molecules is species-dependent and is not related to the amount of exudate produced. This result indicates that bulk proton-binding characteristics and total proton-active site concentrations on exudate molecules are relatively constant between species, but that the species of bacteria does impact the functionality of the exudates produced, particularly with respect to binding of chalcophile elements and redox reactions involving those elements.