Eiichiro Tanoue

Chemical characterization of protein-like fluorophores in DOM in relation to aromatic amino acids

A systematic survey of the protein-like fluorescence intensities was conducted at 11 stations along the 137°E transect from bay to oceanic areas in the northwestern Pacific using three-dimensional excitation emission matrix (3DEEM) spectroscopy and the concentrations of aromatic amino acids obtained by high-performance liquid chromatography (HPLC) in dissolved organic matter (DOM). The 3DEEM patterns of tyrosine-like and tryptophan-like peaks in protein-like fluorophores were variable across different marine environments. The tyrosine-like peak was observed at all stations and depths, while the tryptophan-like peak was only distinguishable as a clear peak in bay and coastal surface waters. These distribution patterns were similar to those of actual concentrations of tyrosine and tryptophan in total hydrolyzable amino acids (THAA) in DOM. Consequently, the tyrosine- and tryptophan-like fluorescence intensities were interpreted to be correlated to the concentrations of tyrosine and tryptophan, respectively, indicating that tyrosine and tryptophan were responsible for the protein-like fluorescence intensities of DOM. The protein-like fluorescence intensities were also correlated to the concentrations of THAA, suggesting that the dynamics of aromatic amino acids were similar to those of THAA. In addition, protein-like fluorescence intensities may be useful indicators as to the dynamics of not only aromatic amino acids but of THAA in bulk DOM as well. Comparison of the tyrosine- and tryptophan-like fluorescence intensities with the concentrations of aromatic amino acids and THAA suggests that the dissolved amino acids were components of relatively small peptides and not protein molecules.

Dissolved Organic Matter in Oceanic Waters

The amount of information on oceanic dissolved organic matter (DOM) has increased dramatically in the last decade thanks to the advances in chemical characterization. This information has supported the development of some novel and important ideas for DOM dynamics in the ocean. Consequently, we have a better understanding of the importance of DOM in oceanic biogeochemical cycles. Here we review studies published mainly during 1995–2001, synthesize them and discuss unsolved problems and future challenges. The measurement, distribution and turnover of dissolved organic carbon (DOC) are presented as the bulk dynamics of the oceanic DOM. The size spectrum, elemental composition, and chemical compositions at molecular and functional group levels are described. The mechanisms proposed for the survival of biomolecules in DOM are discussed.

Distribution and alteration of amino acids in bulk DOM along a transect from bay to oceanic waters

Abstract A systematic survey of the concentrations and composition of total hydrolyzable amino acids (THAA) in bulk dissolved organic matter (DOM) was conducted at 11 stations along the 137°E transect from bay to oceanic areas in the northwestern Pacific. Concentrations of THAA and their contributions to dissolved organic carbon were high in the bay and coastal areas, declined toward the oceanic area and decreased with depth in the water columns. From the distribution patterns of the relative abundances of amino acids along the transect, individual amino acids were divided into four groups. One group included tyrosine, valine, isoleucine, phenylalanine, leucine and tryptophan, and was considered to represent easily degradable THAA, while glycine and alanine belonged to a more biorefractory group of THAA. Principal components analysis (PCA) was conducted to quantitatively differentiate patterns of amino acid composition. Amino acid groups based on PCA agreed with the groups classified by distribution patterns, indicating that first principal component scores reflected the degree of degradation of THAA in DOM, and were defined as a degradation index (DI). Two amino acids, glycine and alanine, increased in relative abundance with increasing DI, while valine, isoleucine, phenylalanine and leucine decreased with decreasing DI. The agreement indicated that the degradation process was the key factor controlling the quantity and quality of THAA in bulk DOM.

Chemical and Biological Studies of Particulate Organic Matter in the Ocean

This paper presents a review of the past decades highlights of research on the isolation and characterisation of particulate organic matter (POM) in the worlds oceans. The emphasis is on chemical studies but, in keeping with the growing interdisciplinary nature of marine science, advances in other disciplines are also discussed, particularly those in biological sciences. Increasing evidence for the importance of picoplankton, bacteria and viruses as POM constituents is highlighted, including the recent recognition of large populations of autotrophic bacteria able to harvest light for energy. The transport of POM to bottom waters was thought to be largely confined to large, rapidly sinking faecal pellets. However, recent studies have highlighted the importance of organic aggregates and flocs formed by diatoms such as Rhizosolenia and other microalgae. Ascending particles have also been discovered, many of which are lipid-rich. Several studies have shown that resuspension of bottom sediments and lateral advection of material from continental shelves can lead to anomalously high particle fluxes measured in sediment traps moored in deep water. Many new approaches for characterizing POM have emerged, such as pyrolysis gas chromatography-mass spectrometry and direct temperature-resolved mass spectrometry for analysis of higher molecular weight materials and biopolymers. Lipid biomarker techniques have also advanced, exciting new possibilities being raised by the ability to measure stable and radioactive carbon isotopes for individual compounds. The techniques of molecular biology, such as the polymerase chain reaction (PCR), are being increasingly applied to provide complementary information to more conventional microscopy and flow cytometry on the identity of organisms in the sea. The combination of these techniques with advanced chemical analysis methods promises to greatly increase our knowledge of the origins, transport and fate of organic matter in the oceans.

In situ production of chromophoric dissolved organic matter in coastal environments

[1] The horizontal and vertical distribution of marine humic-like fluorophore, namely, chromophoric dissolved organic matter (CDOM) fluorescence, was surveyed in Ise Bay, Japan. The distribution patterns of salinity and marine humic-like fluorescence intensity suggested that riverine humic-like fluorophore conservatively distributed along with fresh-sea water mixing in surface water at Ise Bay. However, analysis of mixing behavior of riverine CDOM implied that the 25.1 ± 10.6% in average of bulk marine humic-like fluorescence intensity of Ise Bay surface waters was derived not from a terrestrial origin but an in situ production. A degradation experiment using natural plankton demonstrated the rapid production of marine humic-like fluorophore within a day. The results consistently suggested that in situ production of marine humic-like fluorophore plays an important role in the dynamics of CDOM in coastal environments.

Detection of dissolved protein molecules in oceanic waters

Abstract A method for the extraction and detection of dissolved protein molecules in oceanic waters is described. The procedure involves three separate steps: (1) crude concentration of dissolved protein from seawater by tangential flow ultrafiltration, (2) further concentration and purification of dissolved protein by precipitation with trichloroacetic acid, and (3) separation and detection of dissolved proteins by sodium dodecylsulfate-polyacrylamide gel electrophoresis. Dissolved proteins were successfully extracted with this technique; a relatively limited number of protein molecules (less than 30) were separated and visualized on gels as major bands during the analysis of water from stations located from the subarctic to the tropical Pacific. The majority of proteins had molecular masses ranging from 14 to 66 kilodaltons (kDa). Electrophoretic patterns of dissolved proteins changed both horizontally and vertically in seawater, but some protein molecules were found in all the samples examined. The major proteins detected were relatively pure and were present at high levels. The accumulation of appreciable amounts of a relatively limited number of proteins leads to the hypothesis that particular proteins that make up the majority of the dissolved protein components in seawater are derived from specific sources and contribute quantitatively to the oceanic pool of organic nitrogen.

Close coupling between seasonal biological production and dynamics of dissolved inorganic carbon in the Indian Ocean sector and the western Pacific Ocean sector of the Antarctic Ocean

The distribution of total dissolved inorganic carbon (DIC) in surface sea water and the upper water column of the seasonal ice zone in the Antarctic Ocean between 30°E and 150°E was investigated in the austral summer 1992/1993. In February–March 1993, total DIC content of surface seawater in the seasonal ice zone showed large spatial variability, ranging from 2064 to 2166 μmol kg-1. Biological activity played an important role in the deficit of total DIC in Prydz Bay, in the marginal ice zones (MIZ) near Lutzow-Holm Bay and Casey Bay, and in the offshore regions near 63°S, 100°E, while the decrease in total DIC due to meltwater input from the receding sea ice was also significant in those MIZ and in the area off the West Ice Shelf. From the analyses of total DIC concentration in the coldest waters (t<−1.7°C) of the subsurface temperature minimum layer, we deduced a characteristic value of normalized total DIC concentration (2184.0±3.7 μmol kg-1 at S=34) for the winter mixed layer over the wide area we investigated. Seasonally integrated net community production (NCP) in summer and its ΔCT/ΔN/ΔP ratios were calculated on the basis of the difference in normalized total DIC and nutrients concentrations between the winter mixed layer and the Summer Surface Water. Large spatial variations in the NCP, ranging from 10 to 48 gC m-2, and different ΔCT/ΔN/ΔP consumption ratios, typically 58/9.2/1 and 84/9.0/1, suggest the high variability of organic matter production and of its impact on both the air-sea CO2 exchange and export of carbon from the photic layer to the deeper waters in the seasonal ice zone of the Antarctic Ocean.

Molecular mass distribution and fluorescence characteristics of dissolved organic ligands for copper(II) in Lake Biwa, Japan

Abstract Molecular mass distribution and fluorescence characteristics of organic ligands for copper(II) in freshwater were, for the first time, investigated using ultrafiltration, immobilized metal ion affinity chromatography (IMAC) and three-dimensional excitation-emission matrix spectroscopy (3DEEM). Two types of humic-like fluorescence (Peaks A and B) were found in all molecular ligand fractions, while an additional type of protein-like fluorescence (Peak C) was only observed in the 0.1 μm-GF/F molecular ligand fractions. The Ex/Em maxima of Peak A in the

Fluorescence and amino acid characteristics of molecular size fractions of DOM in the waters of Lake Biwa

Dissolved organic matter (DOM) in the waters from Lake Biwa, Japan was fractionated using tangential flow ultrafiltration, and subsequently characterized by fluorescence properties and amino acids. While major dissolved organic carbon (DOC), UV absorbance (Abs), humic-like fluorescence (Flu) and total hydrolyzed amino acids (THAA) occurred in the less than 5 kDa molecular size fraction, they were not evenly distributed among various molecular size fractions. Flu/Abs ratios increased, and THAA/DOC ratios decreased with decreasing molecular size. Humic-like fluorescence occurred in all molecular size fractions, but protein-like fluorescence only occurred in the 0.1 μm-GF/F fraction. Subtle differences in amino acid compositions (both individuals and functional groups) were observed between various molecular size fractions, this may indicate the occurrence of DOM degradation from higher to lower molecular weight. The results reported here have significance for further understanding the sources and nature of DOM in aquatic environments.

Iron(III) hydroxide solubility and humic-type fluorescent organic matter in the deep water column of the Okhotsk Sea and the northwestern North Pacific Ocean

Abstract Vertical distributions of Fe(III) hydroxide solubility were studied in the Okhotsk Sea and the northwestern North Pacific Ocean during May and June 2000. Fe(III) solubility minima (0.35– 0.45 nM ) were present in a narrow depth range (80– 100 m ) below the surface mixed layer at all stations. In general, the Fe(III) solubility levels in intermediate and deep waters are characterized by mid-depth maxima (0.76– 0.86 nM ) at 800– 1250 m depth and, below that, a slight decrease to 0.4– 0.6 nM with depth in association with increase in nutrient, apparent oxygen utilization (AOU) and humic-type fluorescence intensity. The most significant correlation between the Fe(III) solubility and humic-type fluorescence in intermediate and deep waters suggests that the distribution of humic-type fluorescent organic matter may control the distribution of Fe(III) solubility in deep ocean waters. The solubility profiles reveal that dissolved Fe concentrations in deep ocean waters may be controlled primarily by Fe(III) complexation with natural organic ligands, such as marine dissolved humic substances released through the oxidative decomposition and transformation of biogenic organic matter in intermediate and deep waters. In addition, high Fe(III) hydroxide solubility values (1.0– 1.6 nM ) were observed in the surface mixed layer at a station in the northwestern North Pacific Ocean where a phytoplankton bloom was observed. The higher Fe(III) solubility in the surface waters was probably due to a higher concentration or stronger affinity of natural organic Fe(III) chelators, which may be released by dominant phytoplankton and/or bacteria during the spring bloom and probably have a different chemical composition from those found in intermediate and deep waters.