Extracellular Enzyme Activity in the River Elbe during a Spring Flood Event

Abstract

The ecological balance of rivers can be significantly disturbed by floods, increasing the supply of allochthonous material and energy to the fluvial planktonic food web. During spring flooding in the Elbe in 1999, various physicochemical (pH, conductivity, suspended particulate matter (SPM), particulate and dissolved organic carbon (DOC, POC), inorganic nutrients) and biological parameters (concentration of chlorophyll-a, abundance and biomass of bacteria) were studied in connection with the microbial self-cleaning capacity (dissolved and particle-associated extracellular enzyme activity of ten different enzymes). The pattern of dissolved and particulate material was found to differ greatly (regarding dilution and allochthonous input dynamics), with biological parameters displaying partly differing patterns owing to their bioactivity. Hydrolytic activity was detected for all the enzyme categories investigated, with especially high breakdown rates being determined for proteins containing leucine, arginine, and tyrosine. The overall activities of all the microbial extracellular enzymes studied proved to be dominated by the ectoenzymes ((62.8 ± 13.6) %) associated with particulate (particles, aggregates, and bacterial cell walls). The resulting ecological implications for microbial self-cleaning processes in rivers are discussed. Extrazelluläre Enzymaktivität in der Elbe während eines FrühjahrshochwassersDas ökologische Gleichgewicht in Flüssen kann durch Hochwasserereignisse, die zu einer erhöhten Zuführung von allochthonem Material und Energie zum planktonischen Nahrungsnetz führen, deutlich gestört werden. Im Verlauf eines Hochwassers in der Elbe im Frühjahr 1999 wurden verschiedene physikochemische (pH-Wert, Leitfähigkeit, Schwebstoffe (SPM), partikulärer und gelöster organisch gebundener Kohlenstoff (DOC, POC), anorganische Nährstoffe) und biologische Parameter (Chlorophyll-a-Konzentration, Abundanz und Biomasse von Bakterien) im Hinblick auf das Verhalten der mikrobiellen Selbstreinigungskraft (frei gelöste und mit Partikeln assoziierte extrazelluläre Enzymaktivität von 10 unterschiedlichen extrazellulären Enzymen) untersucht. Gelöste und partikuläre Stoffe zeigten ein voneinander deutlich unterschiedliches Verhalten (Verdünnungs-bzw. allochthone Eintragsdynamik), wobei biologische Parameter bedingt durch ihre Bioaktivität partiell abweichende Muster aufwiesen. Für alle untersuchten Enzymkategorien konnte eine hydrolytische Aktivität nachgewiesen werden, wobei für leucin-, arginin-und tyrosinhaltige Proteine besonders hohe Abbauraten bestimmt wurden. Die Gesamtaktivitäten aller untersuchten mikrobiellen extrazellulären Enzyme wurden von den mit partikulärem Material (Partikel, Aggregate, Bakterienzellaußenwände) assoziierten Ektoenzymen ((62.8 ± 13.6) %) dominiert. Die sich hieraus ergebenden ökologischen Implikationen bezüglich mikrobieller Selbstreinigungsprozesse in Flüssen werden diskutiert.

Free and Particle‐associated Extracellular Enzyme Activity and Bacterial Production in the Lower Elbe Estuary, Germany

“…With the exception of aminopeptidase (leucine) activity, which was unexpectedly low, all other peptidases (arginine, glycine, and tyrosine) showed higher values for the Elbe estuary than for the unaffected part of the river Elbe. Moreover, compared to the results from [9] and (Karrasch et al, in prep.) unusually high hydrolysis rates were determined for α-and β-D-galactosidase and phosphatase activity.…”

“…Compared to the investigations carried out in the spring [9] and autumn in the tidally unaffected part of the river Elbe as well as for the river Havel (Karrasch et al, in prep. ), the results of the enzyme activities from the Elbe estuary exhibit in some cases sharp differences.…”

“…Discussion of the high lipase (stearate) activity is not possible because these measurements represent the first publication of this enzyme activity. The difference of the extracellular enzyme activities compared to the tidally unaffected part of the river [9] reflects the particular abiotic and biotic conditions within the estuarine region.…”

“…A more particle-related degradation of organic material is subject to a higher sedimentation probability, leading to a reduced self-purification capability under less turbulent conditions while dissolved free enzymes remain more or less unaffected by the hydrographical situation, representing as it were the dissolved behavior of the first step of biological selfpurification capacity. A different size fraction pattern of the extracellular enzyme activity (exoenzyme < 0.2 µm vs. ectoenzymes Ն 0.2 µm) was determined in a tidally unaffected stretch of the river Elbe during a spring flood [9] and also during autumn for an investigation of the Saale and Elbe (Karrasch et al, in prep.). In both cases the activity of the ectoenzymes clearly dominated the breakdown of OM.…”

“…Some authors have dealt with free dissolved and particle-associated microbial extracellular enzyme activities in rivers, for instance for various rivers in south-eastern Australia [7], the Elbe estuary [8], and the Elbe and other rivers ( [9] and literature cited therein).…”