Ectoenzyme activity and bacterial secondary production in nutrient-impoverished and nutrient-enriched freshwater mesocosms

Abstract

This report presents results on relationships between the kinetics (Vmax and Km) of β-glucosidase (GLCase) and aminopeptidase (AMPase) activity, and dissolved organic carbon (DOC) and bacterial secondary production in freshwater mesocosms of differing degrees of eutrophication. These relationships varied in different mesocosms and depended on the trophic status of water and the exudation rates of organic carbon (EOC) by phytoplankton. Close coupling of bacterial production to Vmax of GLCase activity was observed only in nutrient-enriched mesocosms. The relationship between GLCase and DOC content was also significant in enriched water. There was no correlation between the Vmax, of GLCase and DOC and bacterial production in nutrient-impoverished and control (mesotrophic) enclosures. However, the Vmax of AMPase correlated well to DOC and bacterial production in these mesocosms. AMPase activity did not correlate with DOC and bacterial production in nutrient-impoverished mesocosms. There was no relationship between bacterial biomass and enzyme activity in all studied mesocosms. Comparison of the rates of phytoplankton production of EOC and rates of the bacterial organic carbon demand (BOCD) in nutrient-impoverished mesocosms showed that EOC flux constituted, on average, 90% of BOCD. However, in nutrient-enriched mesocosms EOC contributed only, on average, 27% to the BOCD; thus, in these mesocosms, bacteria were probably organic-carbon limited. It is hypothesized that to bypass substrate limitation, bacteria produced GLCase and AMPase. These enzymes had a high specific activity and high affinity to their substrates and efficiently hydrolyzed polysaccharides and proteins, thereby supplying microorganisms with readily utilizable products of enzyme catalysis.

Bottom up effects on bacterioplankton growth and composition during summer-autumn transition in the open NW Mediterranean Sea

“…It is then worthwhile considering in some detail the relationships between ectoenzyme activities and bacterial abundance and production. For instance in mesocosms experiments, the strong dependence between ectoenzymatic activity and BP as been attributed to substrate-limited conditions (Chrost and Rai, 1993). During our survey, the correlation coefficients between ectoenzymatic activities and production, or between ectoenzymatic activities and total abundance were very close (0.85 versus 0.81, 0.89 versus 0.91, 0.68 versus 0.60 for phosphatase, aminopeptidase and lipase, respectively, Table 3).…”

Storm-stimulated enzymatic decomposition of organic matter in benthic/pelagic coastal meso-cosms

“…2) that degraded proteins and polysaccharides. Combined processes of enzymatic depolymerisation of organic matter and subsequent release and utilization of directly transportable substrates (Hoppe et al 1988) Sampling date (July) can result in higher rates of bacterial secondary production (Chrost 1989, 1993a, Chrost & Rai 1993a, b, Hoppe et al 1993. It was interesting that bacterial assemblages reacted very rapidly to the influx of organic matter.…”

“…GLCase and AMPase activity were measured fluorometrically (Chrost & Rai 1993a). GLCase activity was measured as an increase in fluorescence as the nonfluorescent substrate 4-methylumbelliferyl-P-D-glucopyranoside (MUF-GLC; Sigma) was hydrolyzed to the fluorescent product, 4-methylumbelliferone (MUF).…”

Cell-free extracellular enzymatic activity is linked to seasonal temperature changes: a case study in the Baltic Sea

“…cell-free) in the surrounding waters (Hoppe et al, 2002). Until recently, most EEA in the marine environment was believed to be associated with cells (Hoppe, 1983;Hoppe et al, 2002) leading to the perception that only cellassociated EEs were of ecological significance (Chrost and Rai, 1993;Rego et al, 1985;Someville and Billen, 1983). However, other reports suggested a major contribution of dissolved EEA to the total oceanic EEA pool (Baltar et al, 2010;Baltar et al, 2013Baltar et al, , 2010Karner and Rassoulzadegan, 1995;Keith and Arnosti, 2001;Obayashi and Suzuki, 2008a).…”