9623323 Sinsabaugh Assessing humic inhibition of microbial processes in aquatic systems. Dissolved organic carbon has long been recognized as being a major source of energy in many aquatic ecosystems. However, in most systems the DOC is composed of a heterogeneous mixture of both labile and recalcitrant substances which have not been very well characterized. Previous studies have indicated that a sizable portion of the DOC pool is composed of high molecular weight humic/phenolic compounds that are refractory in nature. Some of these substances may be utilized directly by microorganisms, while others may require enzymatic processing before they can be assimilated. The presence of these phenolic compounds may have an important influence on the processing of DOC. The objective of this study is to investigate the relationship between DOC quality and the nature of the microbial community. Preliminary work has shown that certain fractions of the DOC pool, namely phenolic compounds, can act to both stimulate and inhibit bacterial productivity. Through a series of individual experiments it may be possible to elucidate some of the underlying mechanisms behind this relationship. The PIs propose to examine several parameters which may be linked with bacterial productivity, including extracellular enzyme activities, plasmid screenings, and elementary DOC characterization. These assays will be conducted in both microcosm and field trials.
