15 - Bacterial Response to Variation in Dissolved Organic Matter

Abstract

Dissolved organic matter (DOM) is often the largest input of organic carbon to aquatic ecosystems, and benthic or pelagic bacteria presumably mediate many of the transformations of DOM into biomass or inorganic components. This chapter discusses two independent, but potentially covarying variables that may affect microbial responses: (1) the bulk concentration of DOM, and (2) the known or inferred composition of that DOM. Dissolved organic matter (DOM) is often the largest input of organic carbon to aquatic ecosystems, and benthic or pelagic bacteria presumably mediate many of the transformations of DOM into biomass or inorganic components. The availability of inorganic nutrients has significant effects on bacterial growth, even in ecosystems where ambient nutrient concentrations suggest that they should not be limiting. Extracellular enzymes appear more responsive (greater scope) than bacterial production or respiration, implying that there is sufficient dynamic range for these enzymes to catabolize shifting sources of DOM. Experiments of the commonly assayed enzymes, the two with the highest activity, and greatest scope have a role in N or P acquisition. This pattern again suggests that the availability of inorganic or organic nutrients has a particularly strong regulatory role for degradative activity.