Production and neutral aldose composition of dissolved carbohydrates excreted by natural marine phytoplankton populations

Abstract

Natural populations of diatoms were incubated for 4-12 h with H 13 CO 3Ϫ1 . The production of particulate and dissolved fractions of organic carbon and neutral aldoses (NAld) was followed by gas chromatography/mass spectrometry. The extracellular production rate of dissolved organic carbon (DOC) ranged from 4.1% to 6.4% of total (particulate and dissolved) production rate. Glucose was a major component of the excreted dissolved neutral aldoses (DNAld), and galactose, rhamnose, fucose, xylose, and mannose were found as secondary components of the excreted DNAld. The comparison of NAld composition with cellular products suggests that glucose in the excreted DNAld is composed mainly of storage glucan. On the other hand, the high ratios of dissolved production to total (dissolved and particulate) production of galactose, rhamnose, fucose, xylose, and mannose probably reflect the active excretion of heteropolysaccharides by diatoms. By assuming steady-state concentrations, turnover rates of DOC and DNAld can be estimated from the phytoplankton production of 13 C-labeled material. The estimated turnover rates of DNAld through phytoplankton photosynthesis is 4.2-5.1 times higher than that of total DOC, which indicates the bioreactive nature of DNAld. This high turnover rate of DNAld mainly resulted from the high turnover rate of glucose, and it is likely that dissolved glucan is important as a carbon and energy carrier in the marine food web. The fact that the turnover rates of DNAld, which is considered to constitute heteropolysaccharides, are lower than that of glucose, would suggest that heteropolysaccharides are more resistant to biological degradation than glucan.

Sources and accumulation of organic carbon in the Pearl River Estuary surface sediment as indicated by elemental, stable carbon isotopic, and carbohydrate compositions

“…It is interesting to note that GLU had the same source with RHA and FUC. At the same time, GLU is the dominant neutral sugar in storage polysaccharides, like glucan, which appear to be degraded faster than heteropolysaccharides (Hama and Yanagi, 2001). These authors also suggest that GLU may be the dominant neutral sugar in highly degraded and biorefractory DOM (Hama and Yanagi, 2001).…”

“…At the same time, GLU is the dominant neutral sugar in storage polysaccharides, like glucan, which appear to be degraded faster than heteropolysaccharides (Hama and Yanagi, 2001). These authors also suggest that GLU may be the dominant neutral sugar in highly degraded and biorefractory DOM (Hama and Yanagi, 2001). The similar origin of GLU and deoxysugars (RHA and FUC) in the Pearl River Estuary might suggest the highly degraded organic carbon therein.…”

“…In addition, neutral sugars are proposed as indicators of the bioactivity and diagenetic status of natural samples (Amon and Benner, 2003;Skoog and Benner, 1997). For example, GLU and GAL are abundant as cellular storage products (β-glucan and galactan polymers) in vascular plants and phytoplankton (Kerherve (Cowie and Hedges, 1992;Hama and Yanagi, 2001;Hernes et al, 1996). Another hexose, MAN, is rich in the high molecular weight fraction of dissolved organic matter derived from a marine diatom Thalassiosira weissflogii in culture, and is preferentially removed during heterotrophic decomposition (Aluwihare et al, 1997).…”

Diatom Polysaccharides: Extracellular Production, Isolation and Molecular Characterization

“…The molecular-level characterization of dissolved polysaccharides may provide basic information on the origin, the bioreactivity and the fate of these biopolymers. For example, after monosaccharide analysis Hama and Yanagi reported that the turnover rate of dissolved glucose was the highest among dissolved neutral aldoses, while turnover rates of galactose, mannose, xylose, rhamnose and fucose were similar to each other and markedly lower than glucose [29]. This was a significant finding suggesting that the degree of degradability of autotrophic DOM depends mainly on the relative percentage of glucose with respect to other monosaccharides.…”

Dynamics and Origin of Transparent Exopolymer Particles in the Oyashio Region of the Western Subarctic Pacific during the Spring Diatom Bloom

“…In our study, TIC concentrations were determined with a total alkalinity analyzer (ATT-05, Kimoto Electric Co., Ltd., Japan). DOC production was estimated according to Hama and Yanagi (2001) with a few modifications. The frozen samples were thawed at room temperature (25 • C) and were desalinated using an electro dialyzer (Micro Acilyzer S3, ASTOM Corp., Japan) equipped with AC-220-550 cartridge (CMX-SB/AMX-SB, ASTOM Corp., Japan).…”