Enzymatic Activity, Bacterial Distribution, and Organic Matter Composition in Sediments of the Ross Sea (Antarctica)

Enzymatic activities of aminopeptidase and β-glucosidase were investigated in Antarctic Ross Sea sediments at two sites (sites B and C, 567 and 439 m deep, respectively). The sites differed in trophic conditions related to organic matter (OM) composition and bacterial distribution. Carbohydrate concentrations at site B were about double those at site C, while protein and lipid levels were 10 times higher. Proteins were mainly found in a soluble fraction (>90%). Chloropigment content was generally low and phaeopigments were almost absent, indicating the presence of reduced inputs of primary organic matter. ATP concentrations (as a measure of the living microbial biomass) were significantly higher at site B. By contrast, benthic bacterial densities at site C were about double those at site B. Bacterial parameters do not appear to be “bottom-up controlled” by the amount of available food but rather “top-down controlled” by meiofauna predatory pressure, which was significantly higher at site B. Aminopeptidase and β-glucosidase extracellular enzyme activities (EEA) in Antarctic sediments appear to be high and comparable to those reported for temperate or Arctic sediments and characterized by low aminopeptidase/β-glucosidase ratios (about 10). Activity profiles showed decreasing patterns with increasing sediment depth, indicating vertical shifts in both availability and nutritional quality of degradable OM. Vertical profiles of aminopeptidase activity were related to a decrease in protein concentration and/or to an increase in the insoluble refractory proteinaceous fraction. The highest aminopeptidase activity rates were observed at site C, characterized by much lower protein concentrations. Differences in EEA between sites do not seem to be explained by differences in the in situ temperature (−1.6 and −0.8°C at sites B and C, respectively). Aminopeptidase activity profiles are consistent with the bacterial biomass and frequency of dividing cells. Enzyme substrate affinity was generally dependent upon substrate concentrations. EEA, normalized to bacterial numbers, indicated specific activities comparable to those reported for equally deep sediments at temperate latitudes. Vertical patterns of specific enzymatic activity appeared to be controlled by chloroplastic pigment concentrations that accumulate in the deeper sediment layers. The overall conclusion from the analysis of EEA in Antarctic sediments is that enzyme-dependent transformations of OM proceed at rates similar to those measured in temperate environments. Protein carbon potentially liberated by aminopeptidase activities (12.597 to 26.190 mg of C m⁻² day⁻¹) indicates that the whole protein pool could be mobilized within 1.3 to 17 h. Carbohydrate carbon mobilization (773 to 2,552 mg of C m⁻² day⁻¹) is sufficient to turn over the carbohydrate pool within 16 to 20 h. Such rates are 6 to 45 times higher than fluxes of particulate organic proteins and carbohydrates, indicating an “uncoupled hydrolysis” by the Antarctic benthic assemblages, in which bacteria appear to be able to rapidly exploit episodic OM pulses.     

Extracellular enzyme activity associated with suspended matter in the River Rhine

SUMMARY. 1. Spatial and temporal variations in exoenzymatic proteolysis and alkaline phosphatase activity in the River Rhine were measured fluorometrically using L-leucyi (ß-naphthylamide and methylumbelliferyl phosphate (MUFP), respectively, as test substances.
2. Extracellular proteolytic activity measured in the lower 150-km reach of the river during 1988 followed the changes in the concentration of particulate nitrogen associated with the occurrence of phytoplankton blooms. Alkaline phosphatase activity was not related to the concentration of particulate phosphate and correlated weakly with particulate nitrogen and phytoplankton concentrations.
3. Seasonal observations (1989) in the lower River Rhine and transport studies in a 660-km-long reach of the river (1990) indicated that the variations in the exoenzyme activities were unrelated (or not closely related) to fluctuating bacterial numbers. Exoproteolytic activity correlated well with thymidine incorporation and algal density, confirming indications in the literature that the exoenzyme activity is related to the overall metabolic rate of the bacterial populations.
4. The exoproteolytic activities in the Rhine are similar to the highest observed in eutrophic freshwaters, indicating a rapid turnover of proteins in the river. Bacterial phosphatase activities, measured with MUFP, were similar to those in the few marine and inland waters studied so far. However, phosphate-limited algal blooms, such as reported for the plume of the Rhine in the North Sea, are likely to contribute substantially to hydrolysis of natural organic phosphates.     

Organic matter composition in coastal sediments at Terra Nova Bay (Ross Sea) during summer 1995

We illustrate the spatial and vertical distribution of sediment phytopigments and organic matter biochemical composition at Terra Nova Bay (Ross Sea) during summer 1995. Coastal sediments displayed high phytopigments concentrations associated with huge amounts of labile organic matter largely dominated by proteins. This result was opposite to previous observations in the same area. Such comparison suggested that whilst organic matter quantity in the sediments depended upon the vertical input from the water column, temporal changes in its biochemical composition were related to benthic processes. As considerably high concentrations of biopolymeric organic carbon were found even at 6-cm depth and according to the “loss type” functioning of the coastal waters of the Ross Sea, we stress the summer time occurrence in coastal sediments of an important organic matter burial. Accepted: 24 October 1999     

Extracellular Hydrolytic Enzyme Activities of the Heterotrophic Microbial Communities of the Rouge River: An Approach to Evaluate Ecosystem Response to Urbanization

The potential effects of urbanization on the bioavailability of dissolved organic carbon (DOC) were tested by determining the extracellular enzyme activities of the heterotrophic microbial communities of the Rouge River. The activities of 19 enzymes were monitored across two water samples (river water and groundwater) at different spatial and temporal scales. High phosphatase, esterase, and aminopeptidase activities was observed in site 9 (site most exposed to anthropogenic sources) showed higher concentrations of DOC compared to sites 1 and 8 (sites exposed to less anthropogenic sources), where moderate activities of diverse range of enzymes were observed. High relative contributions of phosphatase, esterase, and aminopeptidase activities to the overall enzyme activity as observed in site 9 stressed the increased importance of peptides as C source for heterotrophic communities and high in-stream carbon processing, which account for high nonspecific extracellular enzyme activities. In contrast, high contribution of glycosyl hydrolases occurred consistently across all sites, which highlights the significance of microbial detrital and plant biomass as carbon sources. Majority of the enzymes showed evidence of activity at various extents during spring and summer. However, higher activities of leucine aminopeptidase, valine aminopeptidase, β-glucosidase, and α-mannosidase were observed in the summer; and alkaline phosphatase and α-glucosidase in the spring. The results presented here suggest a shift in organic carbon bioavailability across all sites of contrasting urbanization, despite similarities in DOC concentrations. Hence, API ZYM technique can be used as an effective indicator of river water and groundwater system health across an urban gradient.     

Nematode biomass and allometric attributes as indicators of environmental quality in a Mediterranean harbour (Ligurian Sea,Italy)

Nematode biomass and allometric attributes (size spectra, body length and width, morphotypes) were measured and related to the environmental quality of sediments of the Genoa-Voltri commercial harbour (Ligurian Sea, NW Mediterranean) to investigate their possible use as ecological indicators. The sediment quality was defined by measuring the level of organic enrichment (quantity and biochemical composition of sedimentary organic matter) and oxygen stress (redox potential).Nematode biomass spectra (NBS) proved to be extremely valuable in determining differences in the environmental quality of sediments on a hundred-metre spatial scale. High peaks of the NBS were observed in the more organic-rich and oxygen-stressed stations probably in relation to a lower diversity of the nematode communities in these stations, with the predominance of tolerant genera such as Paracomesoma and Sabatieria. Among allometric variables, the length was found to be negatively correlated with oxygen concentrations and positively with TOM percentages, whilst the morphotype length/width ratio (L/W) resulted negatively related to oxygen concentrations and organic matter quality (protein:carbohydrate ratio), suggesting that these allometric attributes represent indicators of the functional adaptation of nematodes to the changing environmental conditions.We suggest that in contrast to time-consuming and expertise-requiring nematode taxonomic analysis, biomass and allometric attributes analysis can provide a simpler but comparable tool to assess sediment quality and environmental heterogeneity of harbour ecosystems.     

Degradation of Macromolecular Organic Compounds in a Tropical Lagoon (Ciénaga Grande,Colombia) and its Ecological Significance

Primary production and decomposition of organic substances were investigated in a tropical lagoon during the rainy season. Production and mineralization were measured using the oxygen method. Total bacteria numbers and biomasses were estimated with epifluorescence microscopy, and the enzymatic degradation capacity of model substrates was determined photometrically. These parameters were measured in the water and sediment of the lagoon itself and also in its effluents and incoming waters. The aim of the study was to determine the sites of highest microbial activity in the lagoon and to compare its activity with other coastal water bodies. Since the shallow water lagoon contains a large amount of particulate matter, it was of special interest to study the degradation of this material and its influence on the microbial population. It was found that up to 14 % of the bacteria colonized the particles and that 62 % of the respiration originated in the particle fraction >8 μm. Highest exoenzymatic activities were measured in the sediment and water of the mangrove belt. It is concluded that decomposition and conditioning of particulate organic matter play dominant roles in the recycling of organic carbon in the lagoon.     

Biochemical characteristics of surface sediments on the eastern Weddell Sea continental shelf, Antarctica: is there any evidence of seasonal patterns?

Biochemical characteristics of seafloor sediment off Austasen in the southeastern Weddell Sea were assayed in samples recovered in the early autumn and late spring of 2000 and 2003, respectively. Sediment was separated in the grain-size fractions >200 μm and <200 μm to distinguish biochemical characteristics in the fraction available for benthic suspension feeders (<200 μm). In the bulk sediment, the lipid (LPD) and carbohydrate (CHO) contents were significantly different between seasons with higher LPD content in the early autumn and higher CHO content in the late spring. In the grain-size fractions <200 μm, the LPD and protein (PRT) contents were significantly higher in the early autumn meaning that in this season the fraction available for benthic suspension feeders presented higher nutritive value. The relatively higher CHO concentrations observed in each fraction in the late spring were attributed to refractory matter, whereas the higher PRT and LPD concentrations found during the early autumn were associated with planktonic material settled after the summer phytoplankton bloom. Our results suggest that there is seasonal variation in the composition of organic matter in the sediment, with better nutritive quality in the early autumn, especially in the grain-size fraction available for benthic suspension feeders. These variations also suggest that the benthic community exploits the fresh organic matter accumulated after the summer throughout the Antarctic dark months leaving the sediment almost exhaust of LPD and with higher CHO contents, presumably of refractory nature, at the onset of the seasonal phytoplankton bloom of the following year.     

Particulate matter composition and bacterial distribution in Terra Nova Bay (Antarctica) during summer 1989–1990

Spatial distributions of particulate organic matter (POM) and microbes were investigated during the summer of 1989–1990 in the coastal waters of Terra Nova Bay (Antarctica). The elemental (organic carbon and nitrogen) and biochemical (lipids, proteins, carbohydrates, DNA and RNA) composition of organic matter was related to bacterioplankton abundance, and pico-phytoplankton density. The ATP concentrations were also measured to gather information about the relationships between particulate matter composition and microbial distribution in Antarctic waters. Total seston was characterized by little spatial variation and was unrelated to the distance from the coast. Suspended particulate matter included some terrestrial components but was mostly composed of autochthonous material. POM was characterized by a uniform distribution and homogeneous composition (mostly of phytoplanktonic origin), and was associated with a relatively scarce microbial community characterized at the surface by high picophytoplankton density. The increase with depth of the living carbon fraction suggested an increase in the microheterotrophic community in the deeper water layers. A significant positive relationship between total bacterioplankton density, and carbohydrate and RNA concentrations was found. Similar significant relationships between pico-phytoplankton abundance and lipids, proteins, carbohydrates and nucleic acids were observed. On the basis of the close coupling found between microbiological and chemical compartments, it seems that, in Terra Nova Bay, bacterial distribution depends on suspended matter and in particular to the labile fraction of the organic detritus.     

Water quality,substrate, and distribution of macroinvertebrates in the Patuxent River,Maryland

The distribution of benthic macroinvertebrates in the Patuxent River, Maryland, was analyzed for the period between June 1975 and February 1976. Numerical diversity was analyzed using data collected from seven sampling stations along the nontidal portion of the Patuxent River. Both natural and artificial substrates were examined. Dissolved oxygen, temperature, soil texture, and amount of organic matter were also measured to determine their correlation with the invertebrate distribution measurements. A 2-way ANOVA revealed significant interaction between site and collecting period in the diversity measurements of the natural substrates. This site by collecting period interaction was not observed in the collections made from the artificial substrates. Dissolved oxygen and temperature did not change significantly with distance along the river. Soil texture and organic matter varied significantly with distance. The distribution of benthic macroinvertebrates was more closely correlated to substrate than to water quality. this finding contradicts previous work on this portion of the Patuxent River.     

Physical and chemical characteristics of the sediment in the estuarine region of Cananéia (SP), Brazil

Physical and chemical characteristics of sediment were analyzed at eight sampling areas in the estuarine region of Cananéia (SP), Brazil. The samples were collected in 1995 during four periods; summer, autumn, winter and spring. Total nitrogen and phosphorus concentrations, redox potential, water and organic matter percentage, sand and silt percentage and grain size were determined in six different layers of 20 cm deep columns of sediment. In general, the nutrient concentration and the percentage of organic matter decreased with depth and greater variations were observed in the first centimeter of the samples. Differences in nutrient concentration and organic matter were also observed during the study period. The highest concentrations were recorded during the rainy season (February) as a consequence of an accumulation of organic matter brought into the system by rivers and adjacent flooded areas. In general, the sediments had oxidized characteristics until the 5 or 10 cm depth in areas near the rich coastal vegetation. However, in areas open to the ocean, the entire sediment columns were almost completely oxidized.     

Ecological advantages from light adaptation and heterotrophic-like behavior in Synechococcus harvested from the Gulf of Trieste (Northern Adriatic Sea)

A preliminary study was carried out on a picocyanobacterial mixed culture harvested from the Gulf of Trieste (Northern Adriatic) and identified as Synechococcus spp. both by transmission electron microscopy observations, biliprotein composition and molecular analyses. Absorption and fluorescence spectra revealed phycourobilin and phycoerythrobilin chromophores, suggesting the presence of both CU- and C-phycoerythrin, besides phycocyanobilin chromophores typical for phycocyanins and allophycocyanins. Both biliprotein analyses and molecular identification indicated the presence of at least two Synechococcus subgroups presumably differing either in phycoerythrin type or in physiological traits. Among the exoenzymatic activities acting on different substrates, only aminopeptidase showed high hydrolysis rates and the uptake of organic molecules was positive for leucine but not for thymidine. The protein carbon mobilized was high compared with the leucine incorporation rates, resulting in low percentages of newly mobilized carbon utilized by cultures. The organic carbon incorporated as leucine was compared with the photosynthetically produced one, and the balance between the phototrophic- and heterotrophic-like processes was c. 3 : 1. Our findings suggest that the Synechococcus heterotrophy plays an important role in cell's metabolism, and that the photoheterotrophic behavior, together with their chromatic adaptation capability, might represent the key for the absolute dominance of this genus in the Adriatic Sea.     

Hydrolytic enzymatic activity in deep-sea sediments

Abstract Hydrolytic activities of five enzymes were measured in deep-sea sediment cores at three stations under in situ temperature and pressure in the NE-Atlantic in March/April and July/August 1992. Generally, activity profiles declined vertically in the upper 10 cm of the cores. Experiments under in situ pressure were not significantly different from measurements under surface conditions. The ranking of potential activity rates in the top sediment horizon was: aminopeptidase > esterase > chitobiase > β-glucosidase > α-glucosidase with ratios of 687/174/11/3/1. This is similar to ratios obtained in marine aggregates from the upper mixed layer, thus supporting the idea of pelagic-benthic coupling in the open ocean. The vertical activity profiles show that the biochemical composition, and thereby the nutritive quality of the degradable material, changed with depth in the sediment cores. About 518 mg carbon was potentially mobilized in the 0–1 cm sediment horizon per square meter per day. This contrasts with the input of particulate organic carbon to the sea floor in this area of only 2.74 mg C m² d⁻¹, determined by sediment traps, which indicates that the deep-sea benthic community can rapidly utilize sedimenting particulate organic material and highlights the importance of extracellular enzyme activity in the sediment biogeochemical loop.     

Organic Carbon Degradation in Arctic Marine Sediments,Svalbard: A Comparison of Initial and Terminal Steps

Degradation of marine organic matter under anoxic conditions involves microbial communities working in concert to remineralize complex substrates to CO ₂ . In order to investigate the coupling between the initial and terminal steps of this sequence in permanently cold sediments, rates of extracellular enzymatic hydrolysis and sulfate reduction were measured in parallel cores collected from 5 fjords on the west and northwest coast of Svalbard, in the high Arctic. Inventories of total dissolved carbohydrates were also measured in order to evaluate their potential role in carbon turnover. Polysaccharide hydrolysis rates exhibited substrate-related and, to a lesser extent, depth-related differences (p < 0.0001); laminarin hydrolysis was consistently most rapid at nearly all depths and sites, and fucoidan hydrolysis was least rapid. Although there was a high degree of variability in parallel cores, sulfate reduction rates also exhibited statistically significant depth-and station-related differences. A comparison with data from previous investigations in Svalbard sediments suggests that this variability is linked to substrate availability rather than to organism distribution. Total dissolved carbohydrate concentrations were comparable to those measured in more temperate sediments, and likely comprise a considerable fraction of porewater dissolved organic carbon. A comparison of dissolved carbohydrate inventories with hydrolysis and sulfate reduction rates suggests that the turnover of carbon through the dissolved pool occurs quite rapidly, on the order of a few days to weeks. The transformation of particulate to dissolved organic matter must also be sufficiently rapid to maintain the measured rates of terminal remineralization.     

Redox processes in recent sediments of the river Meuse, The Netherlands

Pore-water concentrations of inorganic solutes were measured at four locations in a recent sedimentation area of the river Meuse in The Netherlands. The pore-water concentration profiles were interpreted using the steady state one-dimensional reaction/transport model STEADYSED1. This model explicitly accounts for the organic matter degradation pathways and secondary redox reactions. Results show that the model reproduces the measured pore-water profiles of redox species reasonably well, although significant divergence is observed for pH. The latter is due to the absence of pH buffering by CaCO₃ in the model. At all locations, methanogenesis is the major pathway of organic matter degradation below 3 cm from the sediment-water interface. However, organic matter degradation rates by methanogenesis may be overestimated, because methane ebullition is not included. Differences in profiles of redox-sensitive ions among the four locations are explained by differences in depositional conditions, in particular the sediment accumulation rate and supply of organic matter.     

Role of Prokaryotic Biomasses and Activities in Carbon and Phosphorus Cycles at a Coastal,Thermohaline Front and in Offshore Waters (Gulf of Manfredonia,Southern Adriatic Sea)

The Western areas of the Adriatic Sea are subjected to inputs of inorganic nutrients and organic matter that can modify the trophic status of the waters and consequently, the microbiological processes involved in the carbon and phosphorus biogeochemical cycles, particularly in shallow coastal environments. To explore this topic, a survey was carried out during the spring of 2003 in a particular hydrodynamic area of the Gulf of Manfredonia, where the potential (P) and real (R) rates of four different microbial exoenzymatic activities (EEA) (α [αG] and ß glucosidases [ßG], leucine aminopeptidase [LAP], and alkaline phosphatase [AP]) as well as the P and R rates of prokaryotic heterotrophic production (PHP), AP as well as the P and R rates of PHP, primary production (PPnet), the prokaryotic and phototrophic stocks and basic hydrological parameters were examined. Three different water masses were found, with a thermohaline front (THF) being detected between the warmer and less saline coastal waters and colder and saltier offshore Adriatic waters. Under the general oligotrophic conditions of the entire Gulf, a decreasing gradient from the coastal toward the offshore areas was detected, with PHP, PPnet, stocks and EEA (αG, ßG, AP) being directly correlated with the temperature and inversely correlated with the salinity, whereas opposite relationships were observed for LAP activity. No enhancement of microbiological activities or stocks was observed at the THF. The use of P or R rates of microbiological activities, which decrease particularly for EEA, could result in discrepancies in interpreting the efficiency of several metabolic processes.     

The role of sediment organic matter composition in larval habitat selection by the polychaete Capitella sp. I

The role of sediment organic matter composition in larval habitat selection by the polychaete Capitella sp. I was investigated using a still water multiple-choice experiment. Specifically, the following question was addressed: what are the roles of sediment labile organic compounds in larval habitat selection? A replicated Latin-square design was used to test larval preferences among sediments collected from five sites (TLC—Tung Lung Chau; VHE—Victoria Harbor east; VH—Victoria Harbor; VHW—Victoria Harbor west; PC—Peng Chau) in the vicinity of Victoria Harbor, Hong Kong. Although mean grain size was not different among sites, water content and the total organic matter were higher in VH Mud but were similar among other sites. Carbohydrate, lipid, and biopolymeric fractions followed the same trend. According to protein content, sites were ranked as: VH > VHW > TLC = VHE > PC. PC Mud had the highest carbohydrate/protein ratio, due to low concentration of protein. According to larval preference, sites were ranked as: TLC = VH = VHW = VHE > PC. Our study shows a precise relationship between sediment biochemical properties and larval habitat selection. Larvae tend to choose sediments with low carbohydrate/protein ratio. Results suggest that types of sediment organic matter may play more important role in the larval habitat selection process of Capitella sp. I than concentration of organic matter alone.     

Impact of environmental factors on couplings between bacterial community composition and ectoenzymatic activities in a lacustrine ecosystem

This study examined the effects of temporal changes in bacterial community composition (BCC) and environmental factors on potential ectoenzymatic activities (α-glucosidase, β-glucosidase, alkaline phosphatase and leucine aminopeptidase) in a lacustrine ecosystem (Sep reservoir, France). BCC was assessed by terminal restriction fragment length polymorphism. Physical parameters, and inorganic and organic nutrient concentrations (dissolved carbohydrates and proteins) were measured in lakes and tributaries. According to the multivariate statistics (redundancy analysis), physical and chemical factors explained the largest part of leucine aminopeptidase activity, whereas the temporal changes of other ectoenzymatic activities were partly dependent on the variations in the BCC. In particular, the occurrence of occasional bacterial populations seemed to explain a lot of the variation in rates and patterns of polymer hydrolysis. The relation observed in this study between the bacterial structure and activity is discussed within the framework of biodiversity–ecosystem functioning.     

An applied ecological approach for the assessment of anthropogenic disturbances in urban wetlands and the contributor river

An applied ecological approach was used to assess the anthropogenic disturbances on the aquatic systems of the Sorocaba river and its wetlands in the Sorocaba-SP municipality (Southeastern Brazil). Two samplings of water, sediment, macroinvertebrates, and macrophytes were performed in 2017, during the rainy season (February) and dry season (June). Traditional limnological methods were applied to the biological material (macrophytes and macroinvertebrates) and limnological variables. In 2017, domestic wastewater and diffuse pollution were the main anthropogenic impacts on the aquatic ecosystems of the Sorocaba municipality. The used approach allowed the verification of the human disturbances on aquatic systems, sediment, biological communities, and landscape. We found that biochemical oxygen demand, thermotolerant coliforms, total phosphorus, dissolved oxygen, and turbidity are above reference concentrations from the Brazilian guideline CONAMA Resolution 357/05. Four macroinvertebrates orders (Diptera, Oligochaeta, Hirudinea, and Gastropoda) and three macrophytes species (Eichhornia crassipes, Salvinia auriculata and Pistia stratiotes) allowed inferring that Sorocaba river and associated wetlands suffer water quality loss due to organic pollution. The major land use classes were anthropogenic agricultural and non-agricultural (75.42%) disturbances, contributing to limnological alterations and low quality of riparian vegetation. Urban wetlands were similar (e.g. sediment properties, limnological variables, bioindicators) and differed from the contributor river, a situation probably related to the wetlands bimodal pulse. Considering the hydric network of tropical countries in the same geographic region, the similar dynamics of the water bodies, and the context of urbanization, the approach can be applied to assess the human disturbances in the region.