Seasonal variation in dimethylsulfoniopropionate related to microphytobenthos composition in intertidal estuarine sediments

Dimethylsulfoniopropionate (DMSP) and algal pigments were measured monthly over 1 yr (May 1997 to June 1998) in intertidal sediments at 2 sampling sites along the Wester- and Oosterschelde (Netherlands). Temperature, salinity and dissolved inorganic nitrogen (DIN) were measured in the pore water and qualitative microscopic observations were made on the microphytobenthos present in the sediment. Both DMSP and pigment content correlated positively with temperature and salinity. However, the chlorophyll a- or fucoxanthin-specific DMSP contents were not affected by temperature, salinity or DIN. Simultaneous peaks of DMSP and chlorophyll a and fucoxanthin were observed in spring and in summer, and at 1 station also in winter. These peaks coincided with increases in epipelic diatoms. The DMSP content correlated with chlorophyll a and fucoxanthin and this relationship improved by excluding samples with a low ratio of fucoxanthin to chlorophyll a (chl a) indicative of a low amount of diatoms relative to other microalgae. The sediment molar ratio of DMSP:chl a was 9.2 ± 5.6 and 5.1 ± 3.6 for the Wester- and Oosterschelde, respectively, values similar to the cellular ratio in cultured diatoms. These results suggest that diatoms were the most important source of DMSP in the sediment. In summer, cyanobacteria and green algae were also present. While cyanobacteria did not contribute to the DMSP content, the data suggest that the amount of DMSP produced by other algae (probably Euglenophytes) produced similar to that produced by diatoms. Hence, microphytobenthos biomass and community composition were the main factors determining the DMSP content in the intertidal sediments of the Schelde estuary. [KEYWORDS: Dimethylsulfoniopropionate ; DMSP ; Diatoms ; Microphytobenthos ; Intertidal sediments ; Pigments

Seasonal variation of dimethylsulfoniopropionate in related to microphytobenthos in estuarine intertidal sediments

Dimethylsulfoniopropionate (DMSP) and algal pigments were measured monthly over 1 yr (May 1997 to June 1998) in intertidal sediments at 2 sampling sites along the Wester- and Oosterschelde (Netherlands). Temperature, salinity and dissolved inorganic nitrogen (DIN) were measured in the pore water and qualitative microscopic observations were made on the microphytobenthos present in the sediment. Both DMSP and pigment content correlated positively with temperature and salinity. However, the chlorophyll a- or fucoxanthin-specific DMSP contents were not affected by temperature, salinity or DIN. Simultaneous peaks of DMSP and chlorophyll a and fucoxanthin were observed in spring and in summer, and at 1 station also in winter. These peaks coincided with increases in epipelic diatoms. The DMSP content correlated with chlorophyll a and fucoxanthin and this relationship improved by excluding samples with a low ratio of fucoxanthin to chlorophyll a (chl a) indicative of a low amount of diatoms relative to other microalgae. The sediment molar ratio of DMSP:chl a was 9.2 ± 5.6 and 5.1 ± 3.6 for the Wester- and Oosterschelde, respectively, values similar to the cellular ratio in cultured diatoms. These results suggest that diatoms were the most important source of DMSP in the sediment. In summer, cyanobacteria and green algae were also present. While cyanobacteria did not contribute to the DMSP content, the data suggest that the amount of DMSP produced by other algae (probably Euglenophytes) produced similar to that produced by diatoms. Hence, microphytobenthos biomass and community composition were the main factors determining the DMSP content in the intertidal sediments of the Schelde estuary. [KEYWORDS: Dimethylsulfoniopropionate ; DMSP ; Diatoms ; Microphytobenthos ; Intertidal sediments ; Pigments]

Production and consumption of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) in a diatom dominated intertidal sediment

Intertidal sediments usually contain a high amount of dimethylsulfoniopropionate (DMSP) and therefore represent environments with a potentially high emission of dimethylsulfide (DMS). However, knowledge on production and release of DMSP in intertidal sediments is limited. Here, we present data on the diel variation of the total DNIS and DMSP content (DMS[P](total)) and the DMS(P) concentration in the porewater (DMS[P](porewater)) in an intertidal sediment covered by diatoms. Measurements were made at low tide during the day and during the night. Both DNIS(P)(total) and DMS(P)(porewater) were constant and did not respond to the changing conditions of light and oxygen in the sediment, indicating that production and consumption processes were in equilibrium. Incubation of diatoms under light/oxic, dark/oxic and dark/anoxic conditions suggested that no large amounts of DMSP were excreted under the different conditions applied. DMS(P)(porewater) was around 100 nM, which was about 3 orders of magnitude lower than DMS(P)(total). Only after the onset of a heavy rainfall DMS(P)porewater in the sediment suddenly increased above 1 muM, which was explained by excretion of DMSP by DMSP-containing microorganisms in response to the osmotic shock. Both DMSP and DMS were rapidly degraded in sediment slurries, especially under oxic conditions, and degradation closely followed first order kinetics. We conclude that although intertidal sediments contain high total amounts of DMSP, a relatively low amount of DMSP is released by the microphytobenthos under naturally fluctuating light and oxygen conditions, and once released, DMSP and DNIS are rapidly degraded in the upper oxygenated sediment. This explains the low flux of DNIS from intertidal sediments to the atmosphere reported in the literature. [KEYWORDS: dimethylsulfoniopropionate (DMSP) dimethylsulfide (DMS), intertidal sediment, diatoms, degradation rates, Diel variation]

Marine Ecology Progress Series 231:37

ABSTRACT: Intertidal sediments usually contain a high amount of dimethylsulfoniopropionate (DMSP) and therefore represent environments with a potentially high emission of dimethylsulfide (DMS). However, knowledge on production and release of DMSP in intertidal sediments is limited. Here, we present data on the diel variation of the total DMS and DMSP content (DMS[P] total ) and the DMS(P) concentration in the porewater (DMS[P] porewater ) in an intertidal sediment covered by diatoms. Measurements were made at low tide during the day and during the night. Both DMS(P) total and DMS(P) porewater were constant and did not respond to the changing conditions of light and oxygen in the sediment, indicating that production and consumption processes were in equilibrium. Incubation of diatoms under light/oxic, dark/oxic and dark/anoxic conditions suggested that no large amounts of DMSP were excreted under the different conditions applied. DMS(P) porewater was around 100 nM, which was about 3 orders of magnitude lower than DMS(P) total . Only after the onset of a heavy rainfall DMS(P) porewater in the sediment suddenly increased above 1 µM, which was explained by excretion of DMSP by DMSP-containing microorganisms in response to the osmotic shock. Both DMSP and DMS were rapidly degraded in sediment slurries, especially under oxic conditions, and degradation closely followed first order kinetics. We conclude that although intertidal sediments contain high total amounts of DMSP, a relatively low amount of DMSP is released by the microphytobenthos under naturally fluctuating light and oxygen conditions, and once released, DMSP and DMS are rapidly degraded in the upper oxygenated sediment. This explains the low flux of DMS from intertidal sediments to the atmosphere reported in the literature

The intracellular sensor NOD2 induces microRNA-29 expression in human dendritic cells to limit IL-23 release.

NOD2 is an intracellular sensor that contributes to immune defense and inflammation. Here we investigated whether NOD2 mediates its effects through control of microRNAs (miRNAs). miR-29 expression was upregulated in human dendritic cells (DCs) in response to NOD2 signals, and miR-29 regulated the expression of multiple immune mediators. In particular, miR-29 downregulated interleukin-23 (IL-23) by targeting IL-12p40 directly and IL-23p19 indirectly, likely via reduction of ATF2. DSS-induced colitis was worse in miR-29-deficient mice and was associated with elevated IL-23 and T helper 17 signature cytokines in the intestinal mucosa. Crohn's disease (CD) patient DCs expressing NOD2 polymorphisms failed to induce miR-29 upon pattern recognition receptor stimulation and showed enhanced release of IL-12p40 on exposure to adherent invasive E. coli. Therefore, we suggest that loss of miR-29-mediated immunoregulation in CD DCs might contribute to elevated IL-23 in this disease