Microbial Interactions with Humic Substances1

Publisher Summary This chapter examines the diverse geochemical and microbial reactivities of humic substances (HS), the role that these complex organics play in a diversity of environments, and their potential applicability to bioremediative strategies. HS are ubiquitous components in the environment and can be readily isolated from nearly all soils, waters, and sediments. They can account for as much as 10% by weight of the total content of many soils and sediments. It is clear that HS interact with microbial populations through a diversity of mechanisms. These interactions may potentially affect the microbial ecology of a specific environment and significantly affect fate and transport of organic and inorganic environmental pollutants. By considering these interactions, strategies for bioremediation of particular pollutants may be improved. HS can be utilized by microorganisms as effective electron acceptors for the oxidative degradation of organic carbon in anaerobic environments. Alternatively, HS in the reduced form can be utilized by microorganisms as effective electron donors for the assimilation of organic carbon coupled to denitrification. These metabolic processes as well as the intrinsic geochemical reactivity of HS are now known to play an important role on the fate and transport of herbicides, pesticides, hydrocarbons, cations, and other important environmental pollutants.