Dissolved Free Amino Acids Research Articles

Benthic decomposition of Zostera marina roots: a controlled laboratory experiment

The initial benthic decomposition of Zostera marina roots was studied in a controlled flow-through chamber experiment for 23 days. Sediment chambers without added roots served as controls. The inflowing and outflowing artificial seawater (ASW) was analyzed for O 2, ΣCO 2, urea-N, NH 4 + and NO 2 −+NO 3 −. Sediment profiles of Eh, particulate organic carbon (POC) and nitrogen, dissolved organic nitrogen (DON), dissolved free amino acids (DFAA), urea-N, NH 4 +, DFAA and urea turnover rates, sulfate reduction and counts of total anaerobic heterotrophic bacteria and different functional groups were determined. Fluxes of O 2, ΣCO 2, urea-N and NH 4 + were stimulated during root decomposition compared to the unamended control. There were indications of stimulated bacterial growth based on counts of total anaerobic heterotrophic bacteria, anaerobic phosphatase utilizers, ammonifyers and sulfate reducers. Independent estimates of nitrogen and carbon incorporation into bacterial biomass during root decomposition indicate that a major fraction of the nitrogen for microbial growth was mobilized from the indigenous particulate organic nitrogen (PON) pool, whereas the energy source for bacterial growth was mainly obtained from the added eelgrass roots. Most of the nitrogen mineralized during root decomposition was incorporated into the bacterial biomass resulting in a low efflux of urea-N and inorganic nitrogen from the sediment to the water column.

Microbial uptake of dissolved organic and inorganic nitrogen in Randers Fjord

Uptake of 15N labeled NH 4 +, NO 3 −, urea and dissolved free amino acids (DFAA) was measured in April and August 2001 at 6 stations along the salinity gradient of Randers Fjord (Denmark) in order to clarify the relative importance of dissolved organic and inorganic nitrogen (DON and DIN) as N sources for the estuarine planktonic microbial community. Although microbial N uptake was generally dominated by DIN (especially NH 4 +), DON (both urea and DFAA) also served as an important N source and occasionally dominated uptake. Uptake of 15N labeled algal derived DON was measured in an attempt to mimic uptake of the complex ambient DON pool. Uptake rates for the algal derived DON in April were similar to those for NH 4 + and even higher than the summed uptake of NH 4 +, NO 3 −, urea and DFAA in August, suggesting that DON other than urea and DFAA, likely dissolved combined amino acids (DCAA), also served as an important N source. In addition, the relative contributions of heterotrophic bacteria and phytoplankton to total microbial N uptake was estimated from bacterial productivity and measured by inhibiting bacterial N uptake with antibiotics.

A comparison of N and C uptake during brown tide ( Aureococcus anophagefferens) blooms from two coastal bays on the east coast of the USA

Blooms of the brown tide pelagophyte, Aureococcus anophagefferens, have been reported in coastal bays along the east coast of the USA for nearly two decades. Blooms appear to be constrained to shallow bays that have low flushing rates, little riverine input and high salinities (e.g., >28). Nutrient enrichment and coastal eutrophication has been most frequently implicated as the cause of A. anophagefferens and other blooms in coastal bays. We compare N and C dynamics during two brown tide blooms, one in Quantuck Bay, on Long Island, NY in 2000, and the other in Chincoteague Bay, at Public Landing, MD in 2002, with a physically similar site in Chincoteague Bay that did not experience a bloom. We found that the primary forms of nitrogen (N) taken up during the bloom in Quantuck Bay were ammonium and dissolved free amino acids (DFAA) while the primary form of N fueling production at both sites in Chincoteague Bay was urea. At both Chincoteague sites, amino acid carbon (C) was taken up while urea C was not. Even though A. anophagefferens has the ability to take up organic C, during the bloom at Chincoteague Bay, photosynthetic uptake of bicarbonate was the dominant pathway of C acquisition by the >1.2 μm size fraction during the day. C uptake by cells <5.0 μm was insufficient to meet cellular C demand based on the measured N uptake rates and the C:N ratio of particulate material. While cells >1.2 μm did not take up much organic C during the day, smaller cells (>0.2 μm) did. Peptide hydrolysis appeared to play an important role in mobilizing organic matter in Quantuck Bay, where amino acids contributed substantially to N and C uptake, but not in Chincoteague Bay. Dissolved organic N (DON), dissolved organic C (DOC) concentrations and the DOC/DON ratio were higher and total dissolved inorganic N (DIN) concentrations were lower at the bloom site in Chincoteague Bay than at the nonbloom site in the same bay. We conclude that A. anophagefferens is capable of using a wide variety of N and C compounds, and that nutrient inputs, biotic interactions and the dominant recycling pathways determine which compounds are available and which metabolic pathways are active at a particular site.

Concentration and distribution of dissolved amino acids in a shallow hydrothermal system, Vulcano Island (Italy)

Hydrothermal systems are known to harbor a large number of microorganisms, but the organic chemical composition of the solution that comprises their potential substrate is largely unknown. Concentrations and distributions of dissolved free amino acids (DFAA) and dissolved combined amino acids (DCAA) were determined in fluids from the moderate-temperature (42–89 °C), shallow hydrothermal system on the volcanically active island of Vulcano, Italy. The seven samples represent three different geological settings on the island; shallow (∼1 m) submarine vents, geothermal wells, and seeps in heated beach sediments, in addition to ambient local seawater from the bay, Baia di Levante. All hydrothermal sites, with one exception, had TDAA concentrations that were 3–114 times higher than local seawater in Baia di Levante. There were large similarities in amino acid concentration and composition among samples from the same geological setting. The highest amino acid concentrations were found at sites with acidic and reducing conditions, which also had the largest freshwater component. An unusually high fraction of the TDAA pool was represented by DFAA (33–87%), possibly due to in situ acid hydrolysis of DCAA to DFAA. Both DFAA and DCAA concentrations were correlated to DOC, indicating similar source and sink functions for these pools. The yield of TDAA (TDAA-carbon as fraction of organic carbon) ranged from 2% to 25%, which is high compared with non-hydrothermal settings, and indicates high biological lability. The mole fraction of β-alanine plus γ-aminobutyric acid (%BALA + GABA) was 2–2.7% of TDAA, also indicating high biological lability. Owing to the high over-all amino acid concentrations, the high fraction of DFAAs, and the high biological lability of the organic matter, organic matter in general and amino acids specifically could represent significant carbon and energy sources for archaea and bacteria in this hydrothermal system. The clear delineation of three different groups of sites with distinct AA composition and concentrations indicates that the different geological settings within this system have the potential for harboring different microbial communities.

Utilization of marine sedimentary dissolved organic nitrogen by native anaerobic bacteria

Bioavailability and chemical composition of dissolved organic nitrogen (DON) in marine pore water were followed and related to bacterial activity in a 14–d anoxic decomposition experiment. For the experiment 0.2–µm filtered pore water from a coastal marine sediment was inoculated with native sediment bacteria. The initial composition of DON was characterized by a high contribution of dissolved free amino acids (DFAA), dissolved combined amino acids (DCAA), and urea, which together accounted for 82% of the DON pool. During the experiment, 54% of the DON was used by bacteria, indicating that DON was readily available to bacterial degradation. The consumption of DFAA and DCAA accounted for more than half of the DON consumed. The unidentified DON pool accounted for 33% of the net DON consumption, and the unidentified DON pool was fully depleted by the end of the experiment. Systematic changes in the amino acid composition occurred with time of incubation, as demonstrated by use of a principal component analysis based on the mole percent contribution of amino acids. The results indicated that amino acids of both the DFAA and the DCAA pools were useful indicators of the diagenetic state of DON. The present study presents the first direct evidence of short‐term (within 14 d) changes in DFAA and DCAA of the DON pool. These changes were similar to decompositional changes in the molecular composition of amino acids observed in traditional studies of bulk sediment diagenesis.

SUMMER INPUTS OF RIVERINE NUTRIENTS TO THE BALTIC SEA: BIOAVAILABILITY AND EUTROPHICATION RELEVANCE

Most nitrogen and phosphorus transported by world rivers to the oceans is associated with dissolved organic matter. However, organic matter as a potential source of N and P has hitherto been largely neglected in studies of coastal microbial food webs. We examined 50 rivers, draining a major part of the Baltic Sea watershed, with respect to summer concentrations, chemical composition, and biological availability of N and P. The broad spectrum of rivers studied enabled us to assess whether the input of terrigenous organic matter can be an important nutrient source, at various levels of anthropogenic loading of inorganic N and P. Concentrations of total N and P ranged from 9 to 220 μmol/L and from 0.14 to 5.56 μmol/L, respectively, with the highest concentrations in the southern part of the Baltic Sea drainage area and in several rivers on the Finnish western coast. Urea and dissolved combined amino acids (DCAA) each constituted 4–20% of dissolved organic nitrogen (DON), while dissolved free amino acids (DFAA) made up <3% of DON. The contribution of urea and amino acids to the DON pool was inversely correlated with DON concentration. Bacterial regrowth bioassays in selected rivers demonstrated that ∼30% of DON and ∼75% of dissolved organic phosphorus (DOP) was potentially available to the indigenous bacterial assemblage of the Baltic Sea, and hence susceptible to mineralization within the pelagic food web. Our study is among the first to demonstrate that bacterioplankton are able to utilize a major part of DON and DOP from a broad spectrum of natural waters. The C:N ratio, absorbance spectra, and fluorescence properties of the organic matter suggest that the observed high bioavailability of DON and DOP was due to a large contribution of organic matter from riverine primary production compared to the humic matter derived from terrestrial vascular plants. In addition, algal and bacterial cells dominated the transport of particulate organic material, further enhancing productivity of coastal waters. No correlations were found between DON bioavailability and the fraction of DON bound in urea and amino acids, indicating a utilization of other N compounds (e.g., amides) by the bacteria. We estimate that the input of summer riverine N to the Baltic Sea consists of 48% dissolved inorganic N, 41% DON, and 11% particulate N. Corresponding values for phosphorus are 46%, 18%, and 36% of dissolved inorganic P, DOP, and particulate P, respectively. During the thermal summer stratification, when freshwater inputs are trapped in the surface layer, rivers contribute ∼30% of N and ∼5% of P needed to support the export production (plankton sedimenting out of the photic layer) in the Baltic Sea. The high availability to bacteria suggests that DOP is a major stimulator of pelagic productivity in the P-limited northern part of the Baltic Sea. Based on reported concentrations in other areas, we suggest that the global contribution of riverine organic N and P to the primary production of coastal waters is comparable to the contribution of inorganic nutrients.

Bacterial influence on amino acid enantiomerization in a coastal marine sediment

The contribution of Dߚisomers of aspartate (Asp), glutamate (Glu), alanine (Ala), and serine (Ser) to the total concentrations of dissolved free amino acids (DFAA), dissolved combined amino acids (DCAA), and total hydrolyzable amino acids (THAA) was studied in a &lt;2,300ߚyrߚold coastal sediment. Concentrations of the different amino acid pools were typically 5 (DFAA), 100 (DCAA), and 20,000 nmol cmߚ3 (THAA), but variable amounts occurred, especially in the surface layer. Dߚamino acids were identified in all three amino acid fractions. The highest concentration of Dߚisomers occurred in the THAA fraction at a depth of 10 cm, where the maximum bacterial density has been observed (Jørgensen et al. 1990; Mar. Ecol. Prog. Ser. 59: 39–54). This coincidence suggests that the Dߚamino acids originated in peptidoglycan of bacterial cell walls. The proportion of DߚAsp, DߚGlu, DߚAla, and DߚSer increased through the pools of DFAA and DCAA to THAA, suggesting a selective removal of Lߚamino acids to Dߚamino acids. The percentage of the four Dߚamino acids in the THAA pool increased with sediment depth to at least 4.3 m (∼2,150 yr). This most likely indicated that peptidoglycan THAA were retained for a longer period of time in a particulate form compared to other proteinaceous material. The contribution of THAA from peptidoglycan to the THAA pool was estimated to range from &gt;9% at the surface to at least 18% at 4.3 m deep, depending on the assumptions used in the calculation. The distribution of amino acid isomers in Aarhus Bay sediment demonstrated that bacterial peptidoglycan contributed to the pool of organic nitrogen (the four analyzed Dߚamino acids made up about 3% of particulate organic nitrogen [PON]). Although the peptidoglycan concentration increased with sediment depth, our observations do not indicate a longߚterm accumulation of peptidoglycanߚderived amino acids.

Characterisation of dissolved combined amino acids in marine waters.

Dissolved combined amino acids (DCAA) are important constituents of the dissolved organic nitrogen (DON) pool in marine environments, although little is known about their sources, dynamics and sinks. The DCAA pool consists of various compounds including proteins and peptides, proteins linked to sugars and amino acids adsorbed to humic and fulvic acids, clays and other materials. The proportions of each of these components and the extent to which they are used by microplankton living within the photic zone are not known. An investigation was carried out, using (15)N isotope dilution techniques, to determine the concentration and composition of dissolved amino acid pools in the marine environment. A near-shore seawater sample was collected and split into fractions to determine the concentrations of dissolved free amino acids (DFAA), DCAA and a <3 kDa dissolved peptide fraction (DPEP; obtained by ultrafiltration). DCAA and DPEP fractions were hydrolysed to yield free amino acids and all samples were analysed by gas chromatography/mass spectrometry (GC/MS) as isobutyloxycarbonyl/tert-butyldimethylsilyl derivatives. The DFAA was the smallest fraction representing approximately 1% of total dissolved amino acids. The majority of DCAA was contained in the low molecular weight DPEP fraction (90%) and was probably as a result of release from phytoplankton and degradation by heterotrophic bacteria.

Sources and sinks of dissolved free amino acids and protein in a large and deep mesotrophic lake

We studied the microbial cycling of dissolved free amino acids (DFAAs) and protein in mesotrophic Lake Constance, Germany, by examining their release by phytoplankton and various heterotrophic organisms and incorporation by heterotrophic bacterioplankton. Release processes of both substrate classes, measured by an isotope dilution approach, comprised, as an annual mean, 15% of primary production and as much as 64% during the clear‐water phase. DFAAs accounted for ~70% of total release during the spring bloom, in the early phase predominantly as photosynthetic extracellular products of rapidly growing algae and toward the end as a result of copepod grazing. Thereafter, during the clear‐water phase, when daphnids were most abundant, release was dominated by protein. At this time, and again in late summer, lysis of grazing‐damaged and senescent algae, including as well the hydrolytic activity of attached bacteria was one of the most important sources of protein. Rotifers, protozoans, and release processes in the fraction &lt;1 ³m were minor sources of DFAA + protein. Concentrations of dissolved combined amino acids (DCAAs) and protein ranged between 750−1,900 and 1−280 nM, respectively, and peaked duringphytoplankton blooms in spring and summer. As an annual mean, concentrations of labile protein constituted 8% of DCAAs, and the ratio of DFAAs to DCAAs was 0.16. About 50% of the DCAAs occurred in the molecular weight fraction between DFAA and 3 kDa and 30% in that &gt;30 kDa. Concentrations of DCAAs &gt;3 kDa were closely correlated to chlorophyll a, suggesting their phytoplankton origin and thus a ready availability. Protein was the preferred bacterial substrate. As an annual mean, its incorporation supported 45% of bacterial biomass produc­tion, compared with 13% by DFAAs. During winter and spring, when DFAA concentrations were highest, DFAA incorporation constituted up to 40% of bacterial production. Annually, the sum of DFAA + protein supported 58% and 80% of the bacterial C and N demand, respectively, indicating that they were the most important bacterial C and N sources.

Benthic fluxes and pore water distributions of dissolved free amino acids in the open Skagerrak

Benthic fluxes of dissolved free amino acids (DFAA) and ammonium were measured at 11 stations with water depths of 112–682 m in the open Skagerrak (north-eastern North Sea). Sediment was incubated together with ambient overlying water at in-situ temperature in a darkened flux incubator on-board ship during three cruises in 1992, 1993 and 1994. The magnitude and direction of the benthic DFAA fluxes were related to parameters characteristic for the stations such as dissolved inorganic nitrogen fluxes, and abundance of meio and macrofauna . Fluxes of DFAA into the sediment correlated to very low effluxes or influxes of ammonium, influxes of nitrate and low abundance of meio and macrofauna. Effluxes of DFAA correlated to effluxes of ammonium and nitrate, and relatively high abundances of fauna. The most common DFAA in the benthic fluxes were aspartic and glutamic acid , serine , glycine, alanine and valine . Pore water concentrations of DFAA were measured at five of the 11 stations. Those DFAA for which the fluxes were large were also the most common in the pore water. Benthic fluxes were also calculated from pore water gradients. For most of the DFAA, the calculated fluxes were underestimated relative to the measured ones, which probably was due to either a too coarse vertical resolution of the pore water gradients in the uppermost part of the sediment, or because the reactions responsible for the net production of DFAA from organic matter took place predominantly on the sediment surface rather than in the sediment. However, the direction of the calculated fluxes was the same as the measured ones. Benthic fluxes of total DFAA (TDFAA; the sum of the nine most abundant individual DFAA) were between −20 and 13 μmol m −2 day −1 with influxes (i.e. negative fluxes) at the deepest stations. TDFAA fluxes across the sediment–water interface were approximately zero to 2.6% of the total dissolved nitrogen flux, 1–20% of the dissolved inorganic nitrogen flux and approximately zero to 12% of the dissolved organic nitrogen (DON) flux. TDFAA in the pore water constituted 1–13% of the pore water DON, similar to the TDFAA/DON ratio in the fluxes.

Amino acids in interstitial waters from ODP Sites 689 and 690 on the Maud Rise, Antarctic Ocean.

Biogenic calcareous and siliceous sediments were drilled at ODP Sites 689 and 690 on the Maud Rise, Antarctic Ocean. We analyzed dissolved combined amino acids (DCAA) and dissolved free amino acids (DFAA) in interstitial waters in order to characterize the amino acids in dissolved organic matter. The DFAA was predominant over the DCAA in interstitial waters at Sites 689 and 690, which contradicted the previous results from interstitial water and seawater studies. The DCAA in the interstitial waters probably originated from calcareous biogenic debris with less amounts of siliceous debris. Although glutamic acid constituted 41% of the total concentration of DCAA, it accounted for only 1% of the total concentration of DFAA due to the adsorption and/or reaction with biogenic carbonate. Ornithine, a nonprotein amino acid, is a decomposed product of arginine and made up 17 mol% of the total DFAA and. The total hydrolyzable amino acids (=DCAA + DFAA) accounted for 5 to 28% of the dissolved organic carbon (DOC) concentration, which implied that high molecular weight organic matter was a major contributor for the DOM (dissolved organic matter) in interstitial waters. Fairly positive correlation between the dissolved manganese and the total DCAA values suggested that the redox condition plays a significant role in controlling the total DCAA content. A small decrease in the sulfate concentration in the interstitial waters from both sites suggested fairly low microbial activity by sulfate-reducing bacteria.

Coupling of biological and physical regimes across the Antarctic Polar Front as reflected by nitrogen production and recycling

Oceanographic samples were collected across the Antarctic Polar Front (APF) region in the vicinity of ∼60°S, 170°W during the US JGOFS program from December 1997 to March 1998. This paper reports the uptake rates of new (nitrate) and regenerated (ammonium and urea) nitrogen measured by 15N tracer techniques together with the levels of ammonium, urea-N and dissolved free amino acids (DFAAs) during December and mid-February–March. The APF was an important biological boundary, and in December rates of new (nitrate) uptake were greatest south of the APF, exceeding 10 mmol m −2 d −1 near the retreating ice edge. In February, nitrate uptake rates were an order of magnitude lower. Rates of ammonium uptake in both periods were greater in the warmer water north of the front. Nitrogen f-ratios varied from 0.50 to less than 0.05, with larger values associated with the >5 μm size fraction at the ice edge and generally lower values north of the APF. Urea was an important nitrogen source north of the APF, and lowered f-ratios there by 22% on average when included as part of total nitrogen uptake. Urea uptake was less important south of the APF. Ammonium concentrations increased dramatically south of the APF later in the season, suggesting a system dominated by regeneration. Seasonal changes in the concentrations of regenerated organic compounds such as urea and DFAAs were less obvious, although DFAAs exhibited consistent maxima in the high flow regions of the APF. A mass balance based of ammonium fluxes suggests that nitrification was significant at locations south of the APF in February. In these nitrate-replete waters, light/mixing conditions in the surface water (the Sverdrup criterion) accounted for over 50% of the variance in nitrate uptake rates. The stability responsible for higher new production south of the APF is due both to the separation of this region from the maximum zonal wind field to the north as well as to melt-water contribution from the retreating ice field. Estimated new production and exportable carbon production exceeded 500 mmol nitrate m −2 yr −1 and 40 g C m −2 yr −1, respectively, south of the APF. Thus, new production in the marginal ice zone of the Southern Ocean rivals that in coastal systems and indicates that this is an important region for export production.

The effect of eelgrass decomposition on sediment carbon and nitrogen cycling: A controlled laboratory experiment

The initial benthic degradation of senescent Zostera marina leaves was studied in controlled flowthrough microcosm chambers for 33 d. Sediment chambers without added eelgrass leaves served as control chambers. The in‐flowing artificial seawater and ouflowing seawater were analyzed for dissolved organic carbon and nitrogen (DOC and DON), total acid‐hydrolyzable amino acids (THAA), dissolved free amino acids (DFAA), urea, NH4+, NO3−, CO2, and O2 during the 33 d of incubation. Sediment profiles of particulate organic carbon and nitrogen, sediment acid‐hydrolyzable amino acids, DON, DFAA, urea, NH4+ and the turnover rate of urea were measured at four different times during the 33 d of incubation. There was an immediate increase in carbon oxidation and the effluxes of DOC, DON, and NH4+ after the addition of eelgrass leaves to the sediment surface. During the course of incubation, 24.3% of the DON efflux was identified as acid‐hydrolyzable amino acids, dissolved free amino acids, and urea in the chambers with eelgrass addition, whereas these compounds accounted for 33.8% of the DON efflux in the control chambers. There were indications of a stimulated bacterial growth on the eelgrass leaves during the first 7 d after leaf addition that was measured as an increase in acid‐hydrolyzable amino acids. Further, there was a gradual increase in acid‐hydrolyzable amino acids in the sediment throughout the incubation that could only be explained as bacterial growth (and/or protein synthesis). Most of the nitrogen for microbial growth was mobilized from the indigenous particulate organic nitrogen pool, whereas it could be inferred that the energy source for bacterial growth was mainly supplied from the added eelgrass leaves. Most of the nitrogen mineralized within the sediment was incorporated into the microbial biomass with a resultant low efflux of inorganic nitrogen from the sediment to the water column.

Bacterioplankton turnover of dissolved free monosaccharides in a mesotrophic lake

Concentrations and bacterioplankton uptake of dissolved free monosaccharides (DFCHO) in relation to bacter‐ioplankton production and phytoplankton biomass were studied in mesotrophic Lake Constance, Germany, from August 1995 to December 1996. Concentrations of total DFCHO, measured by high‐performance liquid chroma‐tography (HPLC) and pulsed amperometric detection, ranged from &lt;20 to 440 nM and exhibited pronounced spatiotemporal variations. Enhanced concentrations of DFCHO were often associated with the breakdown of phy‐toplankton blooms and periods of low phytoplankton growth. Bacterial uptake rates of DFCHO were also enhanced during such events, as well as at peaks of bacterioplankton production (BP). Ratios of uptake of DFCHO/BP, however, indicated that DFCHO concentrations were relatively more important as substrates during periods of low bacterial growth than during phases of intense bacterial growth. Ratios of bacterial uptake of DFCHO/BP from spring to fall ranged from 0.22 to 0.39 in the layer 0–10 m, from 0.17 to 0.56 at 20 m, and from 0.22 to 0.46 at 50 m, respectively. Glucose, galactose, and mannose dominated the DFCHO pool and constituted ∼55 to ∼70 mol%. The analysis of individual turnover times of five DFCHO concentrations from August to November 1995 at 3, 10, and 50 m revealed that the glucose pool turned over most rapidly, followed by galactose and mannose. Glucosamine and fructose always exhibited substantially longer turnover times. Comparisons to previous studies show that DFCHO concentrations are of similar significance for bacterioplankton growth as dissolved free amino acids (DFAA), even though temporal uptake patterns of both substrates are different.

Régulation de l'activité exoprotéolytique bactérienne aux concentrations naturelles en matière organique dissoute dans un marais maritime

The regulation of the bacterial exoproteolytic activity, at natural substrate concentrations, was studied during the survey of an Atlantic coastal marine pond (France). The regulation of this activity occurs at two different levels: on the one hand, at the cellular level, the ectoenzyme synthesis is regulated by hydrolysis substrates, dissolved combined amino acids (DCAA), and end products, dissolved free amino acids (DFAA), in terms of the relative amounts available to the cell, and on the other hand, at the ecosystem level, i.e. the hydrolytic activity, by the total amounts of DCAA and DFAA in situ. The DFAA acts as an inhibitor in enzymatic synthesis; in contrast, dissolved proteins induce the enzymatic synthesis and the exoproteolytic activitiy. These results, obtained in natural concentration conditions, confirm the functioning in situ of the ectoenzymatic activity regulation model of Chróst, until now only validated in an enriched experimental medium.

REGULATORY EFFECTS OF ENVIRONMENTAL CHEMICAL SIGNALS ON SEARCH BEHAVIOR AND FORAGING SUCCESS

To appreciate the mechanisms governing olfactory-mediated behavior, pro- cesses of chemical signal production and transmission in fluid media (air or water) must be understood. With new tools becoming available in analytical chemistry and fluid dy- namics, investigators can now quantitatively address the processes governing chemical signals in field habitats. This study identifies the role of amino acids as signal molecules regulating search behavior and foraging success by estuarine mud snails (Ilyanassa ob- soleta). For the first time, methods are described for measuring chemical signal production, release, and transport in field habitats, over temporal and spatial scales consistent with olfactory information processing. Rates of advection and turbulent mixing were determined, and shear velocities and roughness Reynolds numbers were estimated to characterize bottom boundary layer flows. Nearly instantaneous chemical measurements were made using a computerized microprobe system and conservative tracer to establish the environmental distributions of signal molecules at rates similar to those sampled by olfactory receptor neurons. In addition, we determined the dissolved free amino acid (DFAA) compositions (up to 18 amino acids), concentrations, and effluent release rates for live intact and injured fiddler crabs (Uca pugilator) and hard clams (Mercenaria mercenaria), which are common prey from mud snail habitats. The field site populated by mud snails was found to be more conducive at broadcasting stronger chemical signals over longer distances than most other estuarine and ocean habitats. Live fiddler crabs released amino acids at very low fluxes (0.1 nmol-min-'-g (wet tissue aiass)-V), while live intact clams took up amino acids from seawater. Once injured, hard clams and fiddler crabs released DFAAs at 88 and 6804 nmol-min-1-g-1, respectively. Mud snails were significantly attracted to injured clams and crabs, but not to intact prey, as compared with controls. Synthetic mixtures of amino acids, simulating fluids leaking from injured prey, were also highly attractive. When we tested for effects of amino acid composition, concentration, mean volume flow rate (of chemical input), and flux, in separate experiments, only flux directly correlated with the number of mud snails attracted. The attraction of mud snails is thus more tightly coupled to the physical transport of chemical stimuli than to the molecular properties of specific amino acids.

Net uptake of dissolved free amino acids by the giant clam, Tridacna maxima : alternative sources of energy and nitrogen?

The role of dissolved free amino acids (DFAA) in nitrogen and energy budgets was investigated for the giant clam, Tridacna maxima, growing under field conditions at One Tree Island, at the southern end of the Great Barrier Reef, Australia. Giant clams (121.5-143.7 mm in shell length) took up neutral, acidic and basic amino acids. The rates of net uptake of DFAA did not differ between light and dark, nor for clams growing under normal or slightly enriched ammonium concentrations. Calculations based on the net uptake concentrations typical of the maximum concentrations of DFAA found in coral reef waters (similar to 0.1 mu M)revealed that DFAA could only contribute 0.1% and 1% of the energy and nitrogen demands of giant clams, respectively. These results suggest that DFAA does not supply significant amounts of energy or nitrogen for giant clams or their symbionts.

Seasonal variations of dissolved organic matter in the northern Adriatic Sea

Abstract Concentrations and seasonal variability of dissolved organic carbon (DOC), total dissolved carbohydrates (TDCHO), and dissolved free amino acids (DFAA), were measured in two frontal regions of the northern Adriatic Sea during two surveys (June, 1996 and February, 1997). Colloidal (>1 kDa) and truly dissolved (

Amino acid uptake by the toxic dinoflagellate Alexandrium fundyense

A toxic axenic strain of Alexandrium fundyense is shown to be capable of removing dissolved free amino acids (DFAAs) until concentrations are similar (low nM) to those found in natural waters. Uptake is greatest during exponential growth, rather than during C and/or N-stress as is usual in diatoms and other flagellates. A wide range of amino acids can be taken up, their concentration being decreased within a few hours to the levels observed prior to DFAA addition. The maximum rate of DFAA-N uptake, during early exponential phase, was 0.8 pmol-N cell−1 h−1, equivalent to ≃20% of the total N requirement. More typically, the contribution of DFAA-N was only ≃5%. However, these uptake rates are not sustainable. It is apparent that this organism cannot use amino-N to support significant growth, even though it can take up DFAAs. This, and the fact that the composition of the internal amino acid pool differed from that externally, is further evidence that the N-physiology of this genus is abnormal (differences to other dinoflagellates include an abnormally high concentration of glutamine and arginine, an effective absence of amine X, and release of nitrite during the␣concurrent assimilation of nitrate and ammonium in␣darkness). There is no evidence that the use of DFAAs enhance toxin content, except when cells are supplied with very high (unnatural) concentrations of arginine.

Induction of larval attachment and metamorphosis in the serpulid polychaete Hydroides elegans by dissolved free amino acids:mode of action in laboratory bioassays

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 190:167-178 (1999) - doi:10.3354/meps190167 Induction of larval attachment and metamorphosis in the serpulid polychaete Hydroides elegans by dissolved free amino acids: mode of action in laboratory bioassays Manfred Beckmann*, Tilman Harder, Pei-Yuan Qian** Department of Biology, Hong Kong University of Science and Technology, Clearwater Bay, Kowloon, Hong Kong *Present address: Cardiff School of Biosciences, Cardiff University, PO Box 915, Cardiff CF10 3TL, Wales, UK **Corresponding author. E-mail: boqianpy@ust.hk ABSTRACT: Larval settlement in the serpulid polychaete Hydroides elegans (Haswell) reportedly occurs in response to both an attractive bacterial film and polar, aliphatic dissolved free amino acids (DFAA). In this study, we tested whether the larval metamorphic response was caused by direct DFAA perception or by induction of DFAA-utilizing bacteria in assay dishes. Still-water laboratory assays were performed with sterile measures in the presence and absence of an antibiotic mixture (2.5 x 10-4 M streptomycin, 1.0 x 10-4 M penicillin). In the absence of these antibiotics our results revealed a significant correlation between DFAA decrease rates, bacterial film development and larval metamorphosis within a 24 h assay period. After 12 h, DFAA concentrations decreased below the detection limit of 0.013 µM, the attached bacterial density in assay dishes was approx. 2 x 104 cells mm-2, and larval metamorphosis was insignificantly low (20%). After 24 h, DFAA were no longer detectable, the attached bacterial density was unchanged, and larval metamorphosis was significantly high (50%). In contrast, naturally biofilmed dishes showed a significant metamorphic response of 50% after 12 h. In analogous experiments in the presence of antibiotics, the percentage of larval metamorphosis varied between 3 and 34% after 24 h while the number of attached bacteria was low (0.5 to 5 x 103 cells mm-2). We assume that the metamorphic response in these treatments was caused by inductive, antibiotic-resistant bacteria. Our results suggest that larval metamorphosis was exclusively triggered by an inductive bacterial film rather than by direct larval perception of DFAA. Despite most sterile measures at the set-up of bioassays, bacteria were inevitably inoculated into test dishes as they were found associated with the larva and suspended in the larval culture water. Therefore, our results point to a systematic error in this established assay procedure. If putative signaling compounds serve as a nutrition source for larval settlement inducing marine bacteria, we conclude that an explicit investigation of a chemical metamorphic cue's efficacy is unreliable. The ecological significance of the transformation of DFAA into an attractive bacterial film for larval attachment and metamorphosis in H. elegans is discussed. KEY WORDS: Hydroides elegans · Polychaete · Amino acids · Antibiotics · Biofilm · Bacteria · Metamorphosis · Settlement induction Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 190. Publication date: December 14, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.