Concentrations Of Total Hydrolysable Amino Acids Research Articles

Distribution and bioavailability of dissolved and particulate organic matter in different water masses of the Southern Yellow Sea and East China Sea

As the largest marginal seas, the Southern Yellow Sea (SYS) and the East China Sea (ECS) are important areas to study the biogeochemical cycles of organic matter from different sources. Seawater samples were collected from the SYS and ECS to determine the composition of organic carbon and major biochemicals (amino acids and carbohydrates) making up the dissolved (DOM) and particulate organic matter (POM). Concentrations of dissolved organic carbon (DOC) in the surface waters exhibited a latitudinal gradient, with high values appearing in the Yellow Sea Coastal Current Water (YSCCW). As the labile fraction of DOM, the concentrations of total hydrolysable amino acids (THAA) and total dissolved carbohydrates (TDCHO) were variable and tended to decrease from inshore to offshore sites. The DOC, THAA, and TDCHO concentrations were negatively correlated with salinity, suggesting that physical mixing and lateral transport played an important role in the distribution of DOM. In contrast, phytoplankton production directly affected the particulate amino acid (PAA) concentrations. High concentrations of PAA in the bottom water along a transect were probably due to resuspension by strong currents. DOC-normalized yields of THAA and TDCHO (THAA-C% and TDCHO-C%) were used to characterize the bioavailability of DOM in different water masses. Elevated THAA-C% values occurred in regions with high phytoplankton biomass, while high TDCHO-C% values were widespread in the Yellow Sea Warm Current Water (YSWCW) and the YSCCW. THAA-C% and TDCHO-C% had similar depth distributions, higher in the surface and middle layers than in the bottom layer, suggesting that organic matter undergoes diagenetic alterations as it sinks. The degradation index (DI) of DOM was lower than that of POM, which could be explained by their different sources and degradation states. The sporadic occurrence of hot spots likely represented important sites of biological activity. • Concentration, chemical composition, and bioavailability of OM were studied. • Physical mixing and lateral transport affect the distribution of DOM. • Amino acid and carbohydrate yields decreased with water depth. • Hot spots of bioavailable DOM occur sporadically in the surface water.

Source, distribution and degradation of sedimentary organic matter in the South Yellow Sea and East China Sea

Sedimentary organic matter (SOM) plays an important role in marine carbon and nitrogen cycling, but the sources, degradation states and fates of SOM are not well understood. In the present study, we determined the total organic carbon (TOC), total nitrogen (TN), stable carbon isotope (δ13C), and total hydrolysable amino acids (THAA) to elucidate the sources and degradation states of SOM in the South Yellow Sea (SYS) and the East China Sea (ECS). THAA concentrations ranged from 4.90 to 29.13 μmol/g, with a mean of 11.03 ± 5.06 μmol/g. The distribution pattern of THAA was similar to that of TOC (r = 0.782, P < 0.01) and TN (r = 0.865, P < 0.01), with higher THAA concentrations in the coastal areas. Based on the two end-member mixing model, the fraction of terrestrial organic matter (Ft) ranged from 12.11% to 51.34% (average: 30.17 ± 9.61%), with much higher variability at the nearshore stations compared to the offshore stations. The C/N ratios and the δ13C values showed the different distribution trend, and there was a negative correlation between them (r = −0.479, P < 0.05). Based on the C/N ratios and δ13C values, the SOM in the study area was a mixture of marine organic matter (OM) and soil-derived OM. In addition, our study showed that SOM was dominated by diatomaceous OM compared to carbonate-derived OM and that terrestrial inputs and primary production were the dominant factors controlling the distribution of OM in the study area. Carbon and nitrogen-normalized yields of THAA (THAA-C% and THAA-N%) showed that relatively fresh OM tended to occur in the coastal areas off the Shandong Peninsula. However, the generally low degradation index (DI) values revealed that all SOM in the study area had undergone significant degradation. Glycine increased in relative abundance as the SOM was degraded, while aromatic amino acids (Tyr and Phe) and neutral amino acids (Leu, Ile and Val) had consistently decreasing trends following SOM degradation.

Variation and Reactivity of Organic Matter in the Surface Sediments of the Changjiang Estuary and Its Adjacent East China Sea

AbstractThe Changjiang Estuary and its adjacent sea make up a highly dynamic ecosystem where the processes influencing the sources and degradation of organic matter (OM) in sediments are still not well understood. In this study, we analyzed the total organic carbon (TOC), total nitrogen (TN), stable carbon isotope (δ13C), and total hydrolysable amino acids (THAA) to investigate the distribution and degradation of sedimentary organic matter (SOM). TOC and TN contents ranged from 0.13% to 0.93% and 0.03% to 0.15%, respectively, with elevated values occurring in the muddy areas near the estuary. The δ13C of SOM became increasingly enriched from inshore (−23.5‰) to offshore (−20.5‰), and the TOC/TN molar ratios (C/N ratios) decreased from 8.16 to 5.84, indicating increasing contributions of marine OM. As the labile fraction of bulk OM, THAA concentrations ranged from 1.36 to 11.76 μmol/g and the distribution of THAA was influenced by terrestrial inputs along with the complex hydrography. The δ13C values and C/N ratios indicated that the SOM in the study area was mainly from marine and terrestrial origins (soil derived). The relatively low degradation index (DI) of SOM (mean: −0.57 ± 0.36) indicated that the OM had already undergone extensive degradation. Consistent with previous findings, our results indicated that the degraded OM was adsorbed by fine‐grained particles and selectively transported southward along the coast. The fresh SOM in the sandy area was mainly from in situ production. Additionally, diatoms appeared to be the primary source of the fresh OM buried in the sediments of the study area.

The use of amino acid indices for assessing organic matter quality and microbial abundance in deep-sea Antarctic sediments of IODP Expedition 318

The Adélie Basin, located offshore of the Wilkes Land margin, experiences unusually high sedimentation rates (~2cmyr−1) for the Antarctic coast. This study sought to compare depthwise changes in organic matter (OM) quantity and quality with changes in microbial biomass with depth at this high-deposition site and an offshore continental margin site. Sediments from both sites were collected during the International Ocean Drilling (IODP) Program Expedition 318. Viable microbial biomass was estimated from concentrations of bacterial-derived phospholipid fatty acids, while OM quality was assessed using four different amino acid degradation proxies. Concentrations of total hydrolysable amino acids (THAA) measured from the continental margin suggest an oligotrophic environment, with THAA concentrations representing only 2% of total organic carbon with relative proportions of non-protein amino acids β-alanine and γ-aminobutyric acid as high as 40%. In contrast, THAA concentrations from the near-shore Adélie Basin represent 40%–60% of total organic carbon. Concentrations of β-alanine and γ-aminobutyric acid were often below the detection limit and suggest that the OM of the basin as labile. DI values in surface sediments at the Adélie and margin sites were measured to be +0.78 and −0.76, reflecting labile and more recalcitrant OM, respectively. Greater DI values in deeper and more anoxic portions of both cores correlated positively with increased relative concentrations of phenylalanine plus tyrosine and may represent a change of redox conditions, rather than OM quality. This suggests that DI values calculated along chemical profiles should be interpreted with caution. THAA concentrations, the percentage of organic carbon (CAA%) and total nitrogen (NAA%) represented by amino acids at both sites demonstrated a significant positive correlation with bacterial abundance estimates. These data suggest that the selective degradation of amino acids, as indicated by THAA concentrations, CAA% or NAA% values may be a better proxy for describing the general changes in sedimentary bacterial abundances than total organic matter or bulk sedimentation rates.

Sources, behaviors and degradation of dissolved organic matter in the East China Sea

Concentrations of dissolved organic carbon (DOC), dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON) and its major compound classes—total hydrolysable amino acids (THAA) were measured at 4 cross-shelf transects of the East China Sea in July 2011. Surface concentrations of DOC, DIN, DON and THAA at the nearshore stations were mostly in excess of those found at the offshore sites, indicating either substantial autochthonous production or allochthonous inputs from the Changjiang River. The vertical distributions of DOC, DON and THAA showed similar trends with higher values in the surface layer, whereas the elevated concentrations of DIN were observed in the bottom layer. Major constituents of THAA presented in the study area were glycine, serine, alanine, glutamic acid, aspartic acid and valine. The mole percentages of neutral amino acids increased from surface water to bottom water, whereas acidic and hydroxy amino acids decreased with the water depth. Concentrations of DOC and THAA were negatively correlated to the ΔDIN values (the difference between the real concentration and theoretical concentration), respectively, indicating the coupling relation between dissolved organic matter (DOM) remineralization and nutrient regeneration in the water column. The C/N ratios in the water column exhibited different characteristics with elevated values appearing in the surface and bottom layers. Box and whisker plots showed that both degradation index (DI) values and THAA yields displayed a decreasing trend from the surface layer to the bottom layer, implying increasing degradation with the water depth. Our data revealed that glycine and alanine increased in relative abundance with decreasing DI, while tyrosine, valine, phenylalanine and isoleucine increased with increasing DI.

Concentrations and distributions of amino acids in black and white smoker fluids at temperatures over 200 °C

The distribution of amino acids in seafloor hydrothermal systems was investigated through the determination of the concentrations of total hydrolysable amino acids (THAAs), dissolved free amino acids (DFAAs) and cell density in>200°C black and white smoker fluids sampled from the Mariana Trough. THAA concentrations of>10μM were detected in the black and white smoker fluids, which are higher than those of low temperature (< 53°C) fluids and ambient seawater (< 1μM). 1.4×104–8.6×105cell/ml of microbe was detected from low temperature hydrothermal fluids (< 100°C) and ambient seawater. The concentration of THAAs increased with increasing temperature, although the cell density decreased in high temperature fluid (> 150°C). The bioactivity would be restricted under the high temperature condition.Levels of DFAAs (< 0.7μM) were very low, suggesting that the amino acids existed mainly as polymers in these hydrothermal fluids. The amino acid polymers plausibly derive from biological protein and dissolve during the reaction of hydrothermal fluids along flow paths around the hydrothermal vents.Amino acids are considered to be unstable under hydrothermal condition (> 200°C). However, labile amino acids (e.g., Asp and Ser) were abundant in high temperature fluids. These amino acids would be protected by reaction with inorganic compounds. The behavior of the amino acids derived from organisms around hydrothermal vents would be constrained more by abiotic physico-chemical reactions than biological activities in hydrothermal systems.

Amino acid biogeochemistry and bacterial contribution to sediment organic matter along the western margin of the Bay of Bengal

Six sediment cores collected from various water depths and sampling locations along the western margin of the Bay of Bengal (BOB) were investigated for the total hydrolysable amino acids (THAA) and d-amino acids (d-AA) to understand their distribution, digenetic alteration and bacterial contribution to organic matter (OM). Irrespective of their location, THAA concentrations and yields generally decreased and mol% glycine increased with increasing water depth indicating that OM was degraded during its transit through the water column. Amino acid based degradation index (DI) indicated that OM of the surface sediments of shallow stations, BOB-1 to BOB-3 was relatively fresher than that of deeper stations, BOB-4, BOB-5 and BOB-6. The concentrations and mol% of the d-AA varied from 0.04 to 0.76µmolgdw−1 and 0.3 to 8.5mol%, respectively. Contribution of bacterial peptidoglycan amino acids to THAA (% THAApep/THAA) ranged between 4.0% and 55.0%. Both % THAApep/THAA and mol% d-AAs were significantly (p<0.01) higher in the surface sediments and decreased with sediment core depth. Based on the d-AA yields, bacterial OM accounted for 1.5–15.6% of TOC, and 3.7–50.0% of TN of the sediments of BOB.

Composition and characterization of colloidal organic matter in the coastal surface waters of Qingdao, China

The composition and characterization of dissolved organic matter (DOM) and colloid organic matter (COM) in the coastal surface waters of Qingdao, China were examined. Water samples were collected in Spring 2008 from the Jiaozhou Bay and its adjacent area and fractionated into total dissolved (< 0.45 μm), colloidal (10 kDa–0.45 μm) and cutoff (< 10 kDa) fractions with the cross-flow ultrafiltration (CFF) system. The excitation–emission-matrix (EEM) spectral properties, the absorbance values at 254 nm ( A 254) and dissolved organic carbon (DOC) of the DOM were observed having the colloidal ratios of 8.7%, 6.2%, and 2.2%, respectively, and exhibiting a decreasing trend. Total dissolved carbohydrates (TCHO) and total hydrolysable amino acids (THAA) comprised 24% of the bulk DOC. Among them, the free monosaccharides (MCHO) and dissolved combined amino acids (DCAA）were the major fractions, followed by polysaccharides (PCHO) and dissolved free amino acids (DFAA). Colloidal TCHO and THAA concentrations were 3.2 µM C and 0.3 µM, respectively. They comprised ∼ 35% of the colloid organic carbon (COC), among which PCHO and DCAA were the dominating fractions. The dissolved carbohydrates and amino acids are mostly concentrated in the cutoff fraction. The A 254 values and DOC concentrations inside the Jiaozhou Bay were apparently higher than those outside, while pH and salinity were slightly lower, which might be due to the influence of terrestrial input and the semi-enclosed bay. The distribution pattern of TCHO was found having basically the same as the distributions of A 254 and DOC.

Amino acid biogeochemistry and organic matter degradation state across the Pakistan margin oxygen minimum zone

To assess whether the oxygen minimum zone (OMZ) across the Pakistan Margin causes differences in the lability of sedimentary organic matter, sediments were collected in the core of the OMZ, in the upper and lower transition zones and below the OMZ. Sediment samples were analysed for total nitrogen (TN) and organic carbon (OC) contents, mineral surface area (SA), and total hydrolysable amino acids (THAA) and enzymatically hydrolysable amino acids (EHAA). OC contents and organic carbon per unit of mineral surface area (OC/SA) values were clearly elevated in the core and lower OMZ transition zone. These sediments also contained more labile sedimentary organic matter, as discerned by higher concentrations of THAA and the contribution of N in THAA to TN. A protein amino acid-based degradation index revealed that all sedimentary organic matter has undergone significant degradation, but sediments in the upper OMZ transition zone and below the OMZ are more degraded than inside the OMZ. Changes in amino acid composition during diagenesis are attributed to a combination of factors: (1) selective preservation in which amino acids in cell walls are better preserved than amino acids in cell plasma, (2) formation and accumulation of bacterially derived organic matter; there were relatively more living bacteria in the core of the OMZ and an accumulation of peptidoglycan-derived amino acids in degraded sediments in the upper OMZ transition zone and below the OMZ, and (3) bacterial transformation, as the molar percentages of bacterial transformation products β-alanine (Bala), γ-amino butyric acid (Gaba), and ornithine (Orn), increased with increasing degradation.

Chemical characteristics of dissolved organic nitrogen in an oligotrophic subtropical coastal ecosystem

Water samples were collected from rivers and estuarine environments within the Florida Coastal Everglades (FCE) ecosystem, USA, and ultrafiltered dissolved organic matter (UDOM; <0.7 μm, >1 kDa) was isolated for characterization of its source, bioavailability and diagenetic state. A combination of techniques, including 15N cross-polarization magic angle spinning nuclear magnetic resonance ( 15N CPMAS NMR) and X-ray photoelectron spectroscopy (XPS), were used to analyze the N components of UDOM. The concentrations and compositions of total hydrolysable amino acids (HAAs) were analyzed to estimate UDOM bioavailability and diagenetic state. Optical properties (UV–visible and fluorescence) and the stable isotope ratios of C and N were measured to assess the source and dynamics of UDOM. Spectroscopic analyses consistently showed that the major N species of UDOM are in amide form, but significant contributions of aromatic-N were also observed. XPS showed a very high pyridinic-N concentration in the FCE–UDOM (21.7 ± 2.7%) compared with those in other environments. The sources of this aromatic-N are unclear, but could include soot and charred materials from wild fires. Relatively high total HAA concentrations (4 ± 2% UDOC or 27 ± 4% UDON) are indicative of bioavailable components, and HAA compositions suggest FCE–UDOM has not undergone extensive diagenetic processing. These observations can be attributed to the low microbial activity and a continuous supply of fresh UDOM in this oligotrophic ecosystem. Marsh plants appear to be the dominant source of UDOM in freshwater regions of the FCE, whereas seagrasses and algae are the dominant sources of UDOM in Florida Bay. This study demonstrates the utility of a multi-technique and multi-proxy approach to advance our understanding of DON biogeochemistry.

Organic matter composition in sediments of the Oman Margin

The quantity and biochemical composition of organic matter (OM) in the sediments underlying and below oxygen minimum zone (OMZ) in the Arabian Sea were studied to provide information on the diagenetic processes of organic carbon under different environmental conditions. Concentrations of total organic carbon (TOC), total nitrogen (TN) and total hydrolysable amino acids (THAA) were significantly higher in sediments within rather than below OMZ, while those of total carbohydrates (TCHO) were slightly lower in the latter, suggesting the presence of a larger supply of labile compounds into the sea bottom at the shallower site (i.e. within OMZ). Hydrolysable amino acid and carbohydrate contribution to TOC were even lower (about 10% in surficial sediments) than the values obtained from the abyssal oligotrophic North Pacific, suggesting that OM food availability in the Oman Margin sediments within OMZ was lower than that observed at abyssal depths. The presence of the highest THAA and TCHO concentrations in the top 40 mm of the sediment core at both sites reflected the presence of bioturbation processes. In contrast with the general view of the deep sea as a stable and constant system, below OMZ in the Arabian Sea sediments, some differences were observed in the two investigated cores indicating the presence of a certain spatial variability in OM content and diagenesis.

Determination of protein for studies of marine herbivory: a comparison of methods

Abstract In this study we compared techniques for the estimation of protein for studies of marine herbivory. As an example we use gut fluid from the temperate marine herbivorous fish Kyphosus sydneyanus. There were two components to this work: (1) to compare the ability of spectrophotometric methods to estimate protein in gut fluid; and (2) to determine the effect of freezing digesta samples on the extraction of gut fluid for the measurement of total hydrolysable amino acids (THAA). The Bradford, Lowry, deoxycholate/trichloroacetic acid (DOC/TCA) Lowry and the bicinchoninic acid (BCA) spectrophotometric protein assays were compared for their ability to estimate protein in pooled gut fluid and compared with protein determined by quantitative amino acid analysis using an automated procedure. The spectrophotometric assays all gave differing estimates of protein content and none correlated well with quantitative amino acid analysis. The Lowry and BCA methods gave similar estimates of protein, which were higher than those measured in the same samples by amino acid analysis. Both the DOC/TCA Lowry and the Bradford assay substantially underestimated protein in pooled gut fluid. Internal standard recovery experiments for the protein assays showed interference of colour formation in the Bradford method but not the other spectrophotometric protein assays. This suggested the low values in the Bradford assay were due to gut fluid interfering with colour formation. Therefore, five algal species known to occur in the diet of Kyphosus sydneyanus were selected to test for their interference in the Bradford assay. The algae included three species of phaeophytes, one rhodophyte and one chlorophyte. Extracts from all five algal species interfered with this protein assay to significant but varying degrees. Two methods of extracting gut fluid were compared: (i) method A, which involved removing the gut fluid from the digesta immediately post capture; and (ii) method B, in which samples of digesta were frozen and gut fluid removed later. The fluid from method B gave significantly higher levels of THAA in some gut segments. Freeze–thawing of digesta in method B was thought to be the basis of the increased THAA. This finding suggests that method A more accurately reflects in vivo gut fluid THAA concentrations. The above methodology provides a framework to compare the ability of different herbivorous species at extracting THAA from their diet. These results highlight that the estimation of protein can be affected by methodology and by sample composition, and shows that methods must be optimized for a particular application.