Dissolved Free Amino Acids Concentrations Research Articles

Spatial distribution of dissolved free amino acids in three Iberian Atlantic estuaries

Rivers and estuaries are the main link between land and ocean, transferring significant amounts of dissolved organic carbon. These ecosystems receive large amount of dissolved organic matter (DOM) from diverse sources, both allochthonous and autochthonous. Within this pool, dissolved free amino acids (DFAA) represent the most labile fraction, offering valuable insights into DOM composition and diagenetic processes. Our study focused on three Iberian Atlantic estuaries—Guadalquivir, Guadiana, and Tinto-Odiel— that differ in hydrology, land use and DOM sources. We studied the longitudinal distribution of DFAA and their response to tidal cycles across these estuaries. Despite similar DFAA concentrations between estuaries (176.6 nM to 1770 nM) were found, variations in specific amino acids like glutamic acid, taurine, and aspartic acid pointed to a substantial influence of terrestrial inputs in Guadalquivir and Guadiana estuaries and an anthropogenic influence in Tinto-Odiel. Predominant amino acids—serine, glycine, ornithine, and asparagine —comprised more than 50 mol% of the estuarine DFAA pool. The dominance of serine, glycine, and ornithine indicated substantial DOM degradation, possibly associated with the loss of labile DOM during estuarine transport. Concurrently, asparagine prevalence was linked to allochthonous DOM input particularly associated with terrestrial runoff, lateral input, and anthropogenic activities at estuarine margins. Our results underscore the impact of tidal cycles on DFAA distribution and emphasize the potential of DFAA in unraveling estuarine DOM dynamics and their role as indicators of reactivity and composition in estuarine biogeochemistry.

Spatial microheterogeneity and selective microbial consumption of dissolved free amino acids in an oligomesotrophic lake

AbstractWe studied the cm to m scale spatial distribution of dissolved free amino acids (DFAA) in the upper epilimnion of oligomesotrophic Lake Zurich in 14 sampling campaigns over > 3 years and at various periods of the growing season. During each campaign, 10 sets of 10 simultaneously drawn samples (10 mL, 2 cm distance) were collected from 5 m depth. DFAA concentrations varied by one to > 3 orders of magnitude within sets, providing field evidence for DFAA release from macroscopic point sources and for substantial variability of the in‐situ growth conditions of bacterioplankton metacommunities. There was a tight relationship between the median DFAA concentration per sampling campaign and the compositional heterogeneity of the 15 most common AA: their composition was similar in samples from campaigns with high median DFAA concentrations, indicating that spatial distribution patterns were mainly a result of physical mixing. By contrast, AA composition was spatially variable in campaigns with low median DFAA concentrations, and serine, aspartate, and glycine were disproportionally high in the 10% samples with highest DFAA concentrations. We hypothesized that pelagic bacteria would preferably target pulses of such locally overrepresented AA. Short‐term incubations with radiolabeled tracers revealed substantially higher microbial uptake of serine and, to a lesser extent, aspartate, than of two amino acids with consistently low in situ concentrations (leucine, isoleucine). This illustrates a “preparedness” of the bacterioplankton to preferably incorporate those AAs that are more available in DFAA hotspots.

Variations in concentrations and sources of bioavailable organic compounds in the Indian estuaries and their fluxes to coastal waters

Estuarine organic matter (EOM) supports heterotrophic carbon demand in the estuaries. However, the fraction of bioavailable organic compounds, which are easily assimilated by biological organisms, in the EOM is unclear. We hypothesize that a significant fraction of dissolved EOM is bioavailable and supports heterotrophic activity in the Indian estuaries. In order to test this hypothesis, 26 major, medium and minor Indian estuaries were sampled during wet and dry periods (2011–2012) for dissolved bioavailable organic compounds and dissolved organic carbon (DOC). The mean concentration of total dissolved carbohydrates (TDCHO) and total dissolved proteins (TDPRO) were higher during wet than dry period in contrary to the observations of dissolved free Amino Acids (DFAA). TDPRO:TDCHO and statistical analysis revealed that terrestrial oganic matter contributed significantly to the EOM in the major and medium estuaries during wet period whereas fresh organic matter derived from in situ production contributed in all estuaries during dry period and minor estuaries during wet period. The lower concentrations of TDCHO and DFAA and their contribution to DOC were observed in the Indian than global estuaries suggesting that either efficient utilization of bioavailable organic compounds or less inputs (autochthonous/allochthonous) in the Indian estuaries. Indian estuaries transported an order of magnitude higher concentration of bioavailable organic compounds to the coastal Bay of Bengal (490 × 109 gC y−1) than to the Arabian Sea (50 × 109 gC y−1). The contribution of bioavailable organic compounds to the DOC export was 25% and 7% in the Bay of Bengal and Arabian Sea respectively. This study suggests that EOM contains a significant fraction of bioavailable organic compounds, as hypothesized, which might support heterotrophic carbon demand in the Indian estuaries as well as adjacent coastal waters.

Determination of picomolar dissolved free amino acids along a South Atlantic transect using reversed-phase high-performance liquid chromatography

Abstract Dissolved free amino acids (DFAA) in seawater are a form of nitrogen (N) available for marine microbes. In oligotrophic environments where N-containing nutrients are the limiting factor for microbial growth, N nutrition from DFAA could be crucial, but as yet it is poorly resolved. Measurements of individual DFAA are challenging as concentrations are typically in the low nmol L − 1 range. Here we report modifications to methodology using o-phthaldialdehyde (OPA) derivatization and reversed phase high performance liquid chromatography (HPLC) that provide a 30-fold improvement in sensitivity enabling the detection of 15 amino acids in seawater with a limit of detection as low as 10 pmol L − 1 with accuracy and precision of better than 10%. This analytical methodology is now suitable for the challenging quantitation of DFAA in oligotrophic seawaters. The method was successfully applied to a suite of seawater samples collected on a cruise crossing the South Atlantic Ocean, where concentrations of DFAAs were generally low (sub nmol L − 1 ), revealing basin-scale features in the oceanographic distributions of DFAA. This unique dataset implies that DFAAs are an important component of the N cycle in both near-coastal and open oceans. Further calculations suggest that the proportions of organic N originating from DFAA sources were significant, contributing between 0.2 and 200% that of NH 4 + and up to 77% that of total inorganic nitrogen in the upper 400 m in some regions of the transect.

Spatiotemporal variation of dissolved carbohydrates and amino acids in Jiaozhou Bay, China

Surface seawater samples were collected from Jiaozhou Bay, China, during six cruises (March–May 2010, September–November 2010) to study the distribution of dissolved organic matter including dissolved organic carbon (DOC), total dissolved carbohydrates, namely monosaccharides (MCHO) and polysaccharides (PCHO) and total hydrolysable amino acids. These included dissolved free amino acids (DFAA) and combined amino acids (DCAA). The goal was to investigate possible relationships between these dissolved organic compounds and environmental parameters. During spring, the concentrations of MCHO and PCHO were 9.6 (2.8−22.6) and 11.0 (2.9−42.5) μmol C/L, respectively. In autumn, MCHO and PCHO were 9.1 (2.6−27.0) and 10.8 (2.4−25.6) μmol C/L, respectively. The spring concentrations of DFAA and DCAA were 1.7 (1.1−4.1) and 7.6 (1.1−31.0) μmol C/L, respectively, while in autumn, DFAA and DCAA were 2.3 (1.1−8.0) and 3.3 (0.6−7.2) μmol C/L, respectively. Among these compounds, the concentrations of PCHO were the highest, accounting for nearly a quarter of the DOC, followed by MCHO, DCAA and DFAA. The concentrations of the organic compounds exhibited a decreasing trend from the coastal to the central regions of the bay. A negative correlation between concentrations of DOC and salinity in each cruise suggested that riverine inputs around the bay have an important impact on the distribution of DOC in the surface water. A significant positive correlation was found between DOC and total bacteria count in spring and autumn, suggesting bacteria play an important role in the marine carbon cycle.

High-throughput determination of dissolved free amino acids in unconcentrated freshwater by ion-pairing liquid chromatography and mass spectrometry

We developed a procedure for the direct determination of dissolved free amino acids (DFAAs) in freshwater samples employing ion-pairing liquid chromatography and mass spectrometry. Our approach allowed accurate quantification of subnanomolar concentrations of DFAAs without prior concentration, derivatization or sample clean-up steps, achieving a throughput of three samples per hour. DFAAs were separated on a C-18 resin using tridecafluoroheptanoic acid as an ion-pairing agent controlling the overall retention. The relative standard deviation of DFAA measurements was <10% in samples from the mesotrophic Lake Zurich (Switzerland), and across concentrations of 0.5–500nM. Recoveries of DFAAs ranged from 94 to 102% within the range of 0.2–10nM. The limits of quantification for individual DFAAs varied between 50pM to 2nM (median, 0.5nM). The new method was employed to compare the spatial variability of DFAA concentrations in samples obtained by two devices. Epilimnetic samples of different size (ml, l) were collected at various spatial scales (cm, m, km) with a traditional 5l Friedinger sampler and with a custom-made multi-syringe sampling apparatus. Concentrations of total DFAAs ranged from 30 to 330nM. Alanine, serine, glutamic acid, arginine and glycine constituted 65% of the total pool, while methionine and tryptophan occurred at sub-nM concentrations only. Concentrations of individual DFAAs varied spatially over 2 orders of magnitude. Their spatial distribution was positively skewed, as characterized by rare peaks, most strongly so for glutamate, glycine and asparagine. The composition of DFAAs significantly differed at all examined spatial scales, and this could be mainly attributed to alanine, aspartic acid, and glycine. Our new method equals or outperforms existing ones in terms of sensitivity and reproducibility, while its procedural simplicity renders it superior for the high-throughput analysis of freshwater samples.

Dissolved organic nitrogen bioavailability indicated by amino acids during a diatom to dinoflagellate bloom succession in the Changjiang River estuary and its adjacent shelf

This study investigates the bioavailability and potential nutritional role of dissolved organic nitrogen (DON) in the development and progression of a large-scale dinoflagellate bloom that occurred in the Changjiang River estuary and its adjacent shelf (CJREAS) in the East China Sea (ECS). Three cruises were conducted during the late spring and early summer following the bloom progression, i.e., the termination phase of the diatom bloom, and the initiation/growth and peak phases of the dinoflagellate bloom. Concentrations of dissolved organic carbon (DOC), DON, dissolved inorganic nitrogen (DIN), dissolved free amino acids (DFAA) and dissolved combined amino acids (DCAA) were measured. The degradation index (DI), based on the relative abundance of total dissolved amino acids (TDAA) and amino acids yields was applied to indicate the diagenetic alteration of dissolved organic matter (DOM). During the succession from a diatom to dinoflagellate bloom, a decrease in DON co-occurred with a decrease in DIN. Concentrations of DFAA and DCAA also clearly decreased. The yields of DFAA and the DCAA and DI values decreased concomitantly with an increase in the DOC/DON, indicating that bioavailability of DON was relatively higher during the end stage of the diatom bloom than during the peak of the dinoflagellate bloom. These results indicated that DON may provide a significant portion of the total N demand throughout the duration of the large-scale dinoflagellate bloom under conditions of low DIN availability in the CJREAS.

Temporal dynamics and depth variations of dissolved free amino acids and polyamines in coastal seawater determined by high-performance liquid chromatography

Short-chained aliphatic polyamines (PAs) are a class of labile dissolved organic nitrogen (DON) that has biogeochemical similarities to dissolved free amino acids (DFAAs). Here we investigated the relative contributions of DFAAs and PAs to the total DON pool and their diurnal dynamics at different depths at the Gray's Reef National Marine Sanctuary (GRNMS) in the spring and fall of 2011. A high-performance liquid chromatography (HPLC) method that uses pre-column fluorometric derivatization with o-phthaldialdehyde, ethanethiol, and 9-fluorenylmethyl chloroformate was optimized to measure 20 DFAAs and 5 PAs in seawater simultaneously. The concentrations of DFAAs and PAs varied over 5-fold during individual diurnal cycles and between seasons; and concentrations of the former (tens to hundreds nM) were typically at least one order of magnitude higher than the latter (a few nM). An exception was noted in fall surface water samples when the total PAs reached 159nM and the ratio of PAs to DFAAs was about 2:3. Compositions of individual DFAAs and PAs also exhibited temporal dynamics, with glycine and spermidine consistently the most abundant compound in each pool, respectively. DFAA concentrations appeared to track chlorophyll a, whereas, total PA concentrations were strongly correlated with bacterial cell abundance. Our results indicate that, at least occasionally, PAs may serve as an important DON pool at the GRNMS. This view is in accordance with recent molecular data but contrasts to measurements made in some other marine environments.

Uptake of dissolved free amino acids by four cold-water coral species from the Mediterranean Sea

Dissolved organic matter, which contains many compounds such as lipids, sugars and amino acids, is an important source of carbon and nitrogen for several symbiotic and asymbiotic tropical coral species. However, there is still no information on its possible uptake by cold-water coral species. In this study, we demonstrated that dissolved organic matter, in the form of dissolved free amino acids (DFAA), is actively absorbed by four cold-water coral species from the Mediterranean Sea. Although the uptake rates observed with 3µM DFAA concentration were one order of magnitude lower than those observed in tropical species, they corresponded to 12–50% of the daily excreted-nitrogen, and 16–89% of the daily respired-carbon of the cold-water corals. Consequently, DFAA, even at in situ concentrations lower than those tested in this study, can supply a significant amount of carbon and nitrogen to the corals, especially during periods when particulate food is scarce.

Phytoplankton species‐specific release of dissolved free amino acids and their selective consumption by bacteria

Despite representing only a small fraction of the ocean's dissolved organic matter pool, dissolved free amino acids (DFAA) have high turnover rates and are major nitrogen and carbon sources for bacterioplankton. Both phytoplankton and bacterioplankton assimilate and release DFAA, but their consumption and production are difficult to quantify in nature due to their short residence times (min) as dissolved monomers. We segregated DFAA production by phytoplankton and bacterial consumption by measuring individual DFAA concentrations in four axenic phytoplankton cultures during the exponential growth phase, and also after 4 d incubations in the presence of a natural bacterioplankton community. The amounts and composition of the DFAA pool varied widely among phytoplankton species. The proportion of dissolved organic carbon attributed to DFAA varied among cultures. The picoeukaryotic prasinophyte, Micromonas pusilla, released higher amounts of DFAA than the other species tested (diatoms and dinoflagellate), especially alanine, which has been reported as the dominant individual DFAA in some oligotrophic environments. Community structure of heterotrophic prokaryotes responded to differences in the quality of organic matter released among microalgal species, with Roseobacter‐related bacteria responding strongly to exudate composition. Our results demonstrate the specificity of DFAA extracellular release among several algal species and their preferential uptake by members of bacterial communities.

Release of dissolved free amino acids from biofilms in stream water

We investigated the origin of dissolved free amino acids (DFAA) in stream water focusing on biofilms in the river bed by means of incubation experiments in the laboratory. Stones were placed in the Toyohira River, Hokkaido, Japan, for 3 months, allowing formation of biofilms, and then incubated for 24 h in the laboratory at stream water temperature. After incubation, the composition and concentrations of DFAA in the incubation solution and total hydrolyzed amino acids (THAA) in biofilms were measured by high-performance liquid chromatography. The amount of chlorophyll a (Chl. a) and the number of bacteria were also measured. The DFAA concentration increased greatly in the biofilm incubation solution, but the DFAA composition (mol %) did not change relative to the inception of incubation, where it was similar to stream water. There was no correlation between the increase in DFAA concentration and the THAA concentration, Chl. a amount, or the number of bacteria in biofilms. These results suggest that biofilms are one of the major sources of DFAA in stream water.

Uptake of dissolved free amino acids by the scleractinian coral Stylophora pistillata

This study was designed to assess the importance of dissolved free amino acids (DFAA) as a nitrogen source for the scleractinian coral Stylophora pistillata. For this purpose, experiments were performed using (15)N-enriched DFAAs, and %(15)N enrichment was measured both in animal tissue and zooxanthellae at different DFAA concentrations, incubation time and light levels. As previously observed for urea, which is another source of organic nitrogen, DFAA uptake exhibited a biphasic mode consisting of an active carrier-mediated transport for concentrations below 3 micromol l(-1) and a linear uptake for higher concentrations. The value of the carrier affinity (K(m)=1.23 micromol l(-1) DFAA) indicated good adaptation of the corals to the low levels of DFAA concentrations measured in most oligotrophic waters. DFAA uptake was also correlated with light. The DFAA contribution to the nitrogen requirements for tissue growth was compared to the contribution of ammonia, nitrate and urea, for which uptake was also measured in S. pistillata. Inorganic sources (NH(4)(+) and NO(3)(-)) contributed 75% of the daily nitrogen needs against 24% for organic sources. Taken altogether, dissolved organic and inorganic nitrogen can supply almost 100% of the nitrogen needs for tissue growth.

Behavioral responses to food odor in juvenile marine fish: Acuity varies with species and fish length

This study tested the hypothesis that acuity of behavioral responses to food odor in three commercially important species of marine fish would increase as juvenile length increased. Swimming activity among two size groups of fish was measured in the presence of a series of squid extract dilutions. Increased swimming activity in juvenile Pacific halibut Hippoglossus stenolepis Schmidt, walleye pollock Theragra chalcogramma Pallas, and sablefish Anoplopoma fimbria Pallas was stimulated above threshold concentrations of squid extract, expressed as dilution from full strength. Maximum chemosensory acuity was observed in smaller (8–14 cm total length, TL) Pacific halibut and walleye pollock, while larger sablefish (15–23 cm TL) continued to develop acuity. Response thresholds were highest (10 − 3 dilution) in Pacific halibut, at intermediate levels (10 − 4–10 − 6 dilution) in walleye pollock and smaller sablefish and reached the lowest levels (10 − 13 dilution) in larger sablefish. The widely held view that dissolved free amino acids (DFAA) are the primary chemosensory stimulants for fish food searching may not be valid for sablefish, as they detected squid extract at dilutions containing DFAA that appeared to be far below ambient sea water DFAA concentrations.

Free amino acids in marine aerosols over the western North Pacific Ocean

Abstract Atmospheric input of fixed nitrogen species to the ocean has attracted considerable attention from the viewpoint of the oceanic biogeochemical cycle of nitrogen, although few measurements of organic nitrogen compounds in atmospheric aerosols have been extensively conducted over remote ocean areas. In this study, we report the geographical distribution of dissolved free amino acids (DFAA) in the water-soluble fraction of two size-segregated marine aerosols over the western North Pacific. The concentrations of DFAA showed higher values over the region north of 30°N, whereas they clearly decreased south of 30°N. Approximately 59–96% of DFAA was found in fine-mode particles. Long-range transport from continental sources could largely contribute to DFAA in marine aerosols over the remote North Pacific.

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.

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.

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.

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.

Seasonal variation of dissolved and adsorbed amino acids and ammonium in a near-shore marine sediment

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 170:67-84 (1998) - doi:10.3354/meps170067 Seasonal variation of dissolved and adsorbed amino acids and ammonium in a near-shore marine sediment Angela Landén*, Per O. J. Hall Department of Analytical and Marine Chemistry, Göteborg University, S-412 96 Göteborg, Sweden *E-mail: angela@amc.chalmers.se ABSTRACT: Dissolved free amino acids (DFAA) and ammonium in the pore water of a coastal sediment at a water depth of 40 m were investigated monthly for more than a year, to improve knowledge on how the concentrations and distributions of these dissolved compounds varied during an annual cycle. Seasonal changes in adsorbed amino acids and ammonium were also studied and adsorption coefficients were calculated. Ammonium distribution in the pore water showed clear seasonal trends. In the warmer period (August and September) there were high concentrations in the pore water, and in winter the lowest concentrations were measured. Pore water concentrations of DFAA were in general low, but showed seasonal trends during the year. At the end of summer when the bottom water temperature reached its maximum (about 14°C), the concentrations of DFAA were also at their maxima. However, a response to the input of organic matter to the sediment was also observed as increased pore water DFAA concentrations. The seasonal response was not strong, which probably was due to several processes (e.g. adsorption, degradation and bacterial assimilation) removing DFAA and thereby preventing large pools of DFAA from being built up in the pore water. Adsorption of ammonium followed the concentration of dissolved ammonium in the pore water and there was neither a relation with input of organic matter nor with temperature in the bottom water. The adsorption coefficient (the dimensionless K) for ammonium was 1.07 ± 0.11 and did not vary during the year. The adsorption coefficients for amino acids, which were all higher than K for ammonium, did show seasonal trends and the periods with high concentrations of adsorbed amino acids were related not only to high concentrations of DFAA, but also to recent input of organic matter and probably also to the stimulation of bioturbation as a result of high temperature in the bottom water at the end of summer. The results demonstrated a seasonal variation in K of amino acids, but not ammonium, indicating that the processes controlling dissolved concentrations were substantially different for these compounds. KEY WORDS: Seasonality · Amino acids · Ammonium · Pore water · Coastal sediment · Adsorption · Adsorption coefficients Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 170. Publication date: September 03, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.