Extracellular enzyme activities in benthic cyanobacterial mats: comparison between nutrient- enriched and control sites in marshes ofnorthern Belize

Abstract

Cyanobacterial mats, an important component of the oligotrophic alkaline wetland ecosystems of the Caribbean, are sensitive to nutrient enrichment. In order to elucidate their role in nutrient cycling, we measured extracellular enzyme activities in cyanobacterial mats and underlying sediment exposed to a long-term effect of different salinities and nutrient enrichment. Activities of alkaline phosphatase, leucine-aminopeptidase, arylsulphatase, and β-glucosidase were measured fluorometrically. The distribution of phosphatase activity among different groups of microorganisms in the vertical structure of the mat was visualized using ELF ® 97 phosphate. The activity of all enzymes, except arylsulphatase, was localized mainly in the mat itself and was several times higher than in the underlying sediment. Phosphatase always exhibited the highest activity, followed by leucine-aminopeptidase, arylsulphatase and β-glucosidase. Phosphatase activity was significantly suppressed in P-addition plots under all salinity levels. The remaining enzymes were not significantly influenced by nutrient addition. Cyanobacteria, which formed most of the mat biomass, exhibited no phosphatase activity, with the exception of Chroococcus spp. Hence, we presume that the main sources of extracellular enzymes are different species of bacteria distributed in the mat and the mucilaginous sheaths of cyanobacteria. Sediment type, rather than salinity, seems to have an important influence on the extracellular enzyme production strategies.KEY WORDS: Alkaline phosphatase · Leucine-aminopeptidase · β-glucosidase · Arylsulphatase · Extracellular polymeric substances · Phosphorus Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 44: [11][12][13][14][15][16][17][18][19][20] 2006 located, are characterized by rather extreme conditions in terms of hydrology, nutrient availability and salinity (Rejmánková et al. 1996). These harsh conditions allow the development of thick cyanobacterial mats, harboring great diversity of cyanobacterial species (Rejmánková et al. 2004). Mats are an important component of northern Belizean marshes, constituting a major part of biomass and primary production coupled with both nitrogen fixation and production of large amounts of polysaccharide-rich extracellular polymeric substances (EPS). The production of EPS may be an important direct source of carbon for associated communities of heterotrophic bacteria (Bell et al. 1983, Espeland et al. 2001, while the nitrogen fixed in mats is utilized by non nitrogen-fixing bacteria and macrophytes (Rejmánková & Komárková 2000). Cyanobacterial mats also influence sediment formation in these systems in that large amounts of calcium carbonate are precipitated during photosynthesis forming marl deposits.Little is known about the role of cyanobacterial mats in nutrient cycling. This has become an increasingly important question as these unique wetlands are threatened by accelerated land use and a consequent increase in nutrient loadin...

Importance of Extracellular Enzymes for Biogeochemical Processes in Temporary River Sediments during Fluctuating Dry–Wet Conditions

“…6.6). The high activity levels measured at the beginning of rewetting in both environments, especially those for enzymes involved in polymer degradation (bglucosidase, peptidase and lipase), can be taken as an indication of outlasting of extracellular enzymes during drought, confirming previous findings on the preservation of enzymes during drying (Sirová et al 2006;Fazi et al 2008;Zoppini 2007). Their activities can play an important role in fuelling the bacterial metabolism as they supply organic substrates rich in energy (glucose and fatty acids) and amino acids ready to use for synthesising new biomass.…”

“…Similarly the hydrolyzing capacity of polymers like polysaccharides and lipids (b-glucosidase and lipase activities) was preserved under drought conditions without showing any significant trend. This enzyme activity survival capacity recalls mechanisms found in desiccation-tolerant bacterial cells capable of accumulating proteins, of which many are able to remain stable (Billi and Potts 2002), or the capacity of polysaccharides-rich extracellular polymeric substances (EPS) to favor enzyme preservation (Sirová et al 2006).…”

“…Benthic cyanobacterial mats from marshes of northern Belize, an oligotrophic environment, are exposed to extreme conditions in terms of hydrology, nutrient availability and salinity (Sirová et al 2006). In the cyanobacterial mats alkaline phosphatase exhibited the highest extracellular enzyme activity, followed by leucineaminopeptidase, arylsulphatase, and b-glucosidase.…”

Oxygen evolution in a hypersaline crust: in situ photosynthesis quantification by microelectrode profiling and use of planar optode spots in incubation chambers

“…P limitation, in contrast, was indicated by a high phosphatase activity visualised by ELF-Phosphate hydrolysis (cf. Sirová et al 2006) in the gypsum crusts (data not shown).…”

Mechanisms of Diatom Assembly in a Hydrologically-Managed Subtropical Wetland

“…Mastogloia calcarea , or are dependent on cyanobacterial EPS as substrates for colonization and protection from desiccation and excess UV (Rejmánková and Komárková 2000, Elasri and Miller 1999, Sirová et al 2006, Thomas et al 2006, as well as the nitrogen fixed by cyanobacteria (Paerl et al 2000). In sites with abundant calcareous periphyton, environmental factors explain relatively more variation than spatial factors because dispersal from suitable habitat is not necessary.…”