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Extracellular Enzyme Activity (extracellular + enzyme_activity)
Selected AbstractsExtracellular Enzyme Activities and Carbon Chemistry as Drivers of Tropical Plant Litter DecompositionBIOTROPICA, Issue 3 2004Steven D. Allison ABSTRACT Litter quality parameters such as nitrogen and lignin content correlate with decomposition rates at coarse scales, but fine-scale mechanisms driving litter decomposition have proven more difficult to generalize. One potentially important driver of decomposition is the activity of extracellular enzymes that catalyze the degradation of complex compounds present in litter. To address the importance of this mechanism, we collected 15 Hawaiian plant litter types and decomposed them in fertilized and control plots for up to two years. We measured litter nutrient content and carbon chemistry prior to decomposition, as well as extracellular enzyme activities, mass loss, and litter nutrient content over time. We found that water-soluble carbon content, cellobiohydrolase activities, and polyphenol oxidase activities were significantly correlated with mass loss. Enzyme activities and decomposition rate constants both varied significantly by litter type, and fertilization increased mass loss rates in five litter types. Some litter types that decayed faster under fertilization also showed time-dependent increases in carbon-degrading enzyme activities, but others decayed faster independent of enzyme changes. These results suggest that extracellular enzyme activities partially determine litter decomposition rates, but high soluble carbon content may circumvent the requirement for enzyme-catalyzed decomposition. [source] Aminopeptidase and phosphatase activities in basins of Lake Hiidenvesi dominated by cyanobacteria and in laboratory grown AnabaenaFRESHWATER BIOLOGY, Issue 9 2002JAANA VAITOMAA 1.,Extracellular enzyme activities were examined in freshwater basins representing a transition from hypertrophy to mesotrophy and in axenic cyanobacterial cultures to evaluate the ecological role of extracellular enzyme activities of cyanobacteria. 2.,Aminopeptidase activity was related to the trophic status of the lake basins. The activity was highest in the most eutrophic basin and decreased in the less nutrient-rich basins. Cyanobacteria were the most important autotrophic organisms and aminopeptidase activity was positively associated with cyanobacterial biomass. 3.,In an axenic Anabaena batch culture, nitrogenase activity was several orders of magnitude higher than leucine aminopeptidase activity. Nitrate did not have an effect on aminopeptidase activity or growth, but significantly reduced the rate of nitrogen fixation. A high phosphorus concentration at the beginning of the Anabaena batch-culture experiment resulted in reduced phosphatase activity. 4.,In Lake Hiidenvesi, aminopeptidase activity probably originated mostly from attached bacteria and less so from cyanobacteria. [source] Community composition and activity of prokaryotes associated to detrital particles in two contrasting lake ecosystemsFEMS MICROBIOLOGY ECOLOGY, Issue 3 2006Charles Lemarchand Abstract The composition, distribution and extracellular enzyme activities of bacteria attached to small (2,50 ,m in size) transparent exopolymer and Coomassie-stained proteinaceous particles (TEP and CSP) were examined in two lakes of different trophic status located in the Massif Central of France. TEP concentrations (104,106 particle per L) were significantly higher in the more productive lake and were significantly related to chlorophyll a concentrations. The majority of TEP and CSP were colonized by bacteria that constituted 2.6% and 7.4% of the total 4,,6-diamidino-2-phenylindole-stained bacteria in lakes Pavin and Aydat, respectively. In both lakes, the composition of particle-associated bacteria was different from that of free-living bacteria, the Betaproteobacteria and Bacteroidetes (i.e. former Cytophaga,Flavobacteria group) being the dominant groups on particles. We also found that 2,5 ,m TEP were more colonized than 2,5 ,m CSP in the two lakes, and that TEP colonization was higher in the less productive lake. Measurements of Leucine aminopeptidase and ,-glucosidase activities in fractionated lake water (0.2,1.2, 1.2,5 and >5 ,m fractions) indicated that proteolytic activity was always higher and that particle-associated bacteria have higher enzymatic activities than free-living bacteria. The glycolytic activities in the 1.2,5 and >5 ,m fractions were related to the abundance of TEP. We conclude that small freshwater detrital organic particles constitute microhabitats with high bacterial activities in pelagic environments and, undoubtedly, present significant ecological implications for the prokaryotic community structure and function in aquatic ecosystems. [source] Aminopeptidase and phosphatase activities in basins of Lake Hiidenvesi dominated by cyanobacteria and in laboratory grown AnabaenaFRESHWATER BIOLOGY, Issue 9 2002JAANA VAITOMAA 1.,Extracellular enzyme activities were examined in freshwater basins representing a transition from hypertrophy to mesotrophy and in axenic cyanobacterial cultures to evaluate the ecological role of extracellular enzyme activities of cyanobacteria. 2.,Aminopeptidase activity was related to the trophic status of the lake basins. The activity was highest in the most eutrophic basin and decreased in the less nutrient-rich basins. Cyanobacteria were the most important autotrophic organisms and aminopeptidase activity was positively associated with cyanobacterial biomass. 3.,In an axenic Anabaena batch culture, nitrogenase activity was several orders of magnitude higher than leucine aminopeptidase activity. Nitrate did not have an effect on aminopeptidase activity or growth, but significantly reduced the rate of nitrogen fixation. A high phosphorus concentration at the beginning of the Anabaena batch-culture experiment resulted in reduced phosphatase activity. 4.,In Lake Hiidenvesi, aminopeptidase activity probably originated mostly from attached bacteria and less so from cyanobacteria. [source] Belowground carbon allocation by trees drives seasonal patterns of extracellular enzyme activities by altering microbial community composition in a beech forest soilNEW PHYTOLOGIST, Issue 3 2010Christina Kaiser Summary ,Plant seasonal cycles alter carbon (C) and nitrogen (N) availability for soil microbes, which may affect microbial community composition and thus feed back on microbial decomposition of soil organic material and plant N availability. The temporal dynamics of these plant,soil interactions are, however, unclear. ,Here, we experimentally manipulated the C and N availability in a beech forest through N fertilization or tree girdling and conducted a detailed analysis of the seasonal pattern of microbial community composition and decomposition processes over 2 yr. ,We found a strong relationship between microbial community composition and enzyme activities over the seasonal course. Phenoloxidase and peroxidase activities were highest during late summer, whereas cellulase and protease peaked in late autumn. Girdling, and thus loss of mycorrhiza, resulted in an increase in soil organic matter-degrading enzymes and a decrease in cellulase and protease activity. ,Temporal changes in enzyme activities suggest a switch of the main substrate for decomposition between summer (soil organic matter) and autumn (plant litter). Our results indicate that ectomycorrhizal fungi are possibly involved in autumn cellulase and protease activity. Our study shows that, through belowground C allocation, trees significantly alter soil microbial communities, which may affect seasonal patterns of decomposition processes. [source] Extracellular Enzyme Activities and Carbon Chemistry as Drivers of Tropical Plant Litter DecompositionBIOTROPICA, Issue 3 2004Steven D. Allison ABSTRACT Litter quality parameters such as nitrogen and lignin content correlate with decomposition rates at coarse scales, but fine-scale mechanisms driving litter decomposition have proven more difficult to generalize. One potentially important driver of decomposition is the activity of extracellular enzymes that catalyze the degradation of complex compounds present in litter. To address the importance of this mechanism, we collected 15 Hawaiian plant litter types and decomposed them in fertilized and control plots for up to two years. We measured litter nutrient content and carbon chemistry prior to decomposition, as well as extracellular enzyme activities, mass loss, and litter nutrient content over time. We found that water-soluble carbon content, cellobiohydrolase activities, and polyphenol oxidase activities were significantly correlated with mass loss. Enzyme activities and decomposition rate constants both varied significantly by litter type, and fertilization increased mass loss rates in five litter types. Some litter types that decayed faster under fertilization also showed time-dependent increases in carbon-degrading enzyme activities, but others decayed faster independent of enzyme changes. These results suggest that extracellular enzyme activities partially determine litter decomposition rates, but high soluble carbon content may circumvent the requirement for enzyme-catalyzed decomposition. [source] Bacterial quorum sensing and nitrogen cycling in rhizosphere soilFEMS MICROBIOLOGY ECOLOGY, Issue 2 2008Kristen M. DeAngelis Abstract Plant photosynthate fuels carbon-limited microbial growth and activity, resulting in increased rhizosphere nitrogen (N) mineralization. Most soil organic nitrogen is macromolecular (chitin, protein, nucleotides); enzymatic depolymerization is likely rate limiting for plant nitrogen accumulation. Analyzing Avena (wild oat) planted in microcosms containing sieved field soil, we observed increased rhizosphere chitinase and protease-specific activities, bacterial cell densities, and dissolved organic nitrogen (DON) compared with bulk soil. Low-molecular-weight (MW) DON (<3000 Da) was undetectable in bulk soil but comprised 15% of rhizosphere DON. Extracellular enzyme production in many bacteria requires quorum sensing (QS), cell-density-dependent group behavior. Because proteobacteria are considered major rhizosphere colonizers, we assayed the proteobacterial QS signals N -acyl-homoserine lactones (AHLs), which were significantly increased in the rhizosphere. To investigate the linkage between soil signaling and nitrogen cycling, we characterized 533 bacterial isolates from Avena rhizosphere: 24% had chitinase or protease activity and AHL production; disruption of QS in seven of eight isolates disrupted enzyme activity. Many Alphaproteobacteria were newly found with QS-controlled extracellular enzyme activity. Enhanced specific activities of nitrogen-cycling enzymes accompanied by bacterial density-dependent behaviors in rhizosphere soil gives rise to the hypothesis that QS could be a control point in the complex process of rhizosphere nitrogen mineralization. [source] Turnover of labile and recalcitrant soil carbon differ in response to nitrate and ammonium deposition in an ombrotrophic peatlandGLOBAL CHANGE BIOLOGY, Issue 8 2010PAULINE M. CURREY Abstract The effects of 4 years of simulated nitrogen deposition, as nitrate (NO3,) and ammonium (NH4+), on microbial carbon turnover were studied in an ombrotrophic peatland. We investigated the mineralization of simple forms of carbon using MicroRespÔ measurements (a multiple substrate induced respiration technique) and the activities of four soil enzymes involved in the decomposition of more complex forms of carbon or in nutrient acquisition: N -acetyl-glucosaminidase (NAG), cellobiohydrolase (CBH), acid phosphatase (AP), and phenol oxidase (PO). The potential mineralization of labile forms of carbon was significantly enhanced at the higher N additions, especially with NH4+ amendments, while potential enzyme activities involved in breakdown of more complex forms of carbon or nutrient acquisition decreased slightly (NAG and CBH) or remained unchanged (AP and PO) with N amendments. This study also showed the importance of distinguishing between NO3, and NH4+ amendments, as their impact often differed. It is possible that the limited response on potential extracellular enzyme activity is due to other factors, such as limited exposure to the added N in the deeper soil or continued suboptimal functioning of the enzymes due to the low pH, possibly via the inhibitory effect of low phenol oxidase activity. [source] Interactive effects of elevated CO2, N deposition and climate change on extracellular enzyme activity and soil density fractionation in a California annual grasslandGLOBAL CHANGE BIOLOGY, Issue 10 2005Hugh A. L. Henry Abstract Elevated CO2, N deposition and climate change can alter ecosystem-level nutrient cycling both directly and indirectly. We explored the interactive effects of these environmental changes on extracellular enzyme activity and organic matter fractionation in soils of a California annual grassland. The activities of hydrolases (polysaccharide-degrading enzymes and phosphatase) increased significantly in response to nitrate addition, which coincided with an increase in soluble C concentrations under ambient CO2. Water addition and elevated CO2 had negative but nonadditive effects on the activities of these enzymes. In contrast, water addition resulted in an increase in the activities of lignin-degrading enzymes (phenol oxidase and peroxidase), and a decrease in the free light fraction (FLF) of soil organic matter. Independent of treatment effects, lignin content in the FLF was negatively correlated with the quantity of FLF across all samples. Lignin concentrations were lower in the aggregate-occluded light fraction (OLF) than the FLF, and there was no correlation between percent lignin and OLF quantity, which was consistent with the protection of soil organic matter in aggregates. Elevated CO2 decreased the quantity of OLF and increased the OLF lignin concentration, however, which is consistent with increased degradation resulting from increased turnover of soil aggregates. Overall, these results suggest that the effects of N addition on hydrolase activity are offset by the interactive effects of water addition and elevated CO2, whereas water and elevated CO2 may cause an increase in the breakdown of soil organic matter as a result of their effects on lignin-degrading enzymes and soil aggregation, respectively. [source] Characterization of Tissue Transglutaminase in Human Osteoblast-like CellsJOURNAL OF BONE AND MINERAL RESEARCH, Issue 8 2001Deborah J. Heath Abstract Tissue transglutaminase (tTG) is a calcium-dependent and guanosine 5,-triphosphate (GTP) binding enzyme, which catalyzes the post-translational modification of proteins by forming intermolecular ,(,-glutamyl)lysine cross-links. In this study, human osteoblasts (HOBs) isolated from femoral head trabecular bone and two osteosarcoma cell lines (HOS and MG-63) were studied for their expression and localization of tTG. Quantitative evaluation of transglutaminase (TG) activity determined using the [1,414C]-putrescine incorporation assay showed that the enzyme was active in all cell types. However, there was a significantly higher activity in the cell homogenates of MG-63 cells as compared with HOB and HOS cells (p < 0.001). There was no significant difference between the activity of the enzyme in HOB and HOS cells. All three cell types also have a small amount of active TG on their surface as determined by the incorporation of biotinylated cadaverine into fibronectin. Cell surface-related tTG was further shown by preincubation of cells with tTG antibody, which led to inhibition of cell attachment. Western blot analysis clearly indicated that the active TG was tTG and immunocytochemistry showed it be situated in the cytosol of the cells. In situ extracellular enzyme activity also was shown by the cell-mediated incorporation of fluorescein cadaverine into extracellular matrix (ECM) proteins. These results clearly showed that MG-63 cells have high extracellular activity, which colocalized with the ECM protein fibronectin and could be inhibited by the competitive primary amine substrate putrescine. The contribution of tTG to cell surface/matrix interactions and to the stabilization of the ECM of osteoblast cells therefore could by an important factor in the cascade of events leading to bone differentiation and mineralization. [source] | ||||||||||