The trophic dynamics of riverine bacterioplankton: Relationships among substrate availability, ectoenzyme kinetics, and growth

Abstract

The role of dissolved organic matter (DOM) in the trophic dynamics of aquatic systems is difficult to study. One approach is to focus on the activity of the extracellular enzyme systems that heterotrophic bacteria use to obtain nutrients from DOM. These data are easy to acquire, but difficult to interpret, because we lack general models that relate these activities to the two sides of the trophic reaction: the DOM pool and bacterial production. To address this gap, we collected water samples from the Maumee River on nine dates from May 1996 through November 1996. The water was filtered and placed in bottles to which a variety of substrates were added (final concentration 20 µM unless otherwise noted): ammonium, leucine, albumin (1 mg liter-1), glucose, cellobiose, starch (1 mg liter-l), vanillin, and tannin (2 mg liter-1). After 20 h at ambient river temperature, respiration, productivity, growth efficiency, and the activities of a-glucosidase, P-glucosidase, leucine aminopeptidase, phosphatase, and esterase were measured. The glucosidases were the most responsive enzymes, followed by phosphatase and peptidase. Saccharide and albumin additions produced the largest increases in production and growth efficiency. Phenolic amendments generally depressed growth efficiency. The results suggest that production was primarily carbon limited: Peptides appeared to be a major component of the diet, but high productivities were associated with the availability of saccharides. During the summer, production appeared to be fueled by lysates and exudates generated through the microbial loop. Lower ratios of productivity (e.g., enzyme activity and positive metabolic responses to phenols) suggested that allochthonous carbon may have been important during spring and autumn.

The occurrence of lipolytic bacteria and the activity of extracellular lipases in a riverine ecosystem

“…In the water of the Słupia River, the maxima of the activity of lipases were observed in spring and fall. Similar results were obtained by Foreman et al (1998) in the Maumee River (northwest Ohio) and Boon (1990) in the Kiewa River (south-eastern Australia). The higher activity of lipases observed in spring in the Słupia River could have resulted from the considerable amounts of allochthonous lipids flowing into the water together with the snow melt, while an increased level of the activity of lipases in fall could have been related to heavy rainfall and increased mortality of phytoplankton and zooplankton which brings considerable amounts of lipids into the water (Arts et al 1992).…”

“…The mean lipase activity of the aerobic isolates from a river is 5 × 10 -11 μM MUF min -1 and anaerobic isolates 3 × 10 -13 μM MUF min -1 . The activity of lipases in the water of the Słupia River was low as compared to other rivers (Jones, Lock 1993;Boon 1990;Foreman et al 1998). This low activity of lipid-hydrolyzing enzymes might be due to the fact that in the study area only 5 -8% of heterotrophic bacteria had lipolytic properties.…”

“…However, lipids are often a complex mixture of organic compounds that are too large to be directly incorporated into bacterial cells (Foreman et al 1998). This explains why many bacteria are capable of synthesizing lipases which catalyze reactions of lipid depolymerization.…”

Aerobic and anaerobic degradation of tannic acid on water samples from Monjolinho reservoir (São Paulo, SP, Brazil)

“…The low amount of consumed oxygen could be explained by the fact that tannin depressed enzyme activities and had a little effect on productivity, driving down growth efficiency of microorganisms (Foreman et al, 1998). Another study on tannic acid interaction showed that this polyphenol might lead to the formation of both soluble and insoluble aggregates with proteins.…”

A preliminary study on estimating extra-cellular nitrate reductase activities in estuarine systems

“…The rate-limiting steps in the mineralization of organic matter could be enzyme-induced hydrolysis of macromolecules (Keyhani and Roseman, 1997;Foreman et al, 1998;Grossart et al, 1998). Enzymes mediate a wide variety of biogeochemical chemical reactions, and have been linked to nutrients cycling in soils/sediments (Burns, 1986;Pant and Warman, 2000;Furlan and Pant, 2006) and aquatic systems (Pant et al, 2002).…”