Uptake and excretion of dimethylsulphoniopropionate is driven by salinity changes in the marine benthic diatomCylindrotheca closterium

Abstract

Long-term ( 4 14 d) and short-term ( 4 9 h) effects of salinity on the dimethylsulphoniopropionate (DMSP) content of the marine benthic diatom Cylindrotheca closterium were investigated. When grown in batch cultures at various salinities, intracellular DMSP increased from 13.8 to 823 mmol g 71 protein at salinities of 11 and 44 psu, respectively, but increasing salinity further did not result in a higher content. Instead, the concentration of the amino acid proline increased from 17.5 to 149.6 mmol g 71 protein when salinity increased from 33 to 55, indicating that this compound is more important than DMSP as an osmoprotectant at higher salinities. In addition, another, hitherto unidentified, compound increased strongly in response to salinity. During salinity up-and down-shock experiments, changes in the DMSP content of C. closterium corresponded with the changes in salinity. DMSP was excreted into the medium after salinity down-shock, while salinity upshock induced a slow synthesis of DMSP. However, C. closterium was also able to take up DMSP from the medium; the amount depended on the salinity difference applied. This is the first report of uptake of DMSP by an alga. The results demonstrate that synthesis of DMSP is too slow to be important for short-term acclimation and that its contribution to the intracellular osmotic potential of C. closterium is probably small. However, the observation that uptake of DMSP was faster after salinity up-shock from 11 to 33 than from 11 to 22, indicates that DMSP does have an osmoprotective function in C. closterium. Uptake of DMSP and other organic osmolytes from the environment may serve as a mechanism of osmoacclimation for diatoms living under highly fluctuating salinities in intertidal sediments.

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

“…However, it matches nicely the ratios of 4.5 to 8.7 reported by Kasamatsu et al (2004) for isolates of psychrophilic diatoms. It also agrees with the ratio of 8.2 at a salinity of 33 reported for a culture of the benthic diatom Cylindrotheca closterium by van Bergeijk et al (2003). This can be taken as further evidence for the contribution of diatoms to the DMS(P) production in intertidal sediments.…”

“…intracellular concentration) by different groups or species of algae, or environmental factors influencing the specific DMSP content of algae, such as salinity or nitrogen availability (Turner et al 1988, Iverson et al 1989, Townsend & Keller 1996. DMSP has been suggested to serve as cryo-or osmoprotectant, because its content in marine micro-and macroalgae increases with decreasing temperature or increasing salinity (Sheets & Rhodes 1996, Yoch 2002, van Bergeijk et al 2003, Kasamatsu et al 2004. Furthermore, it has been hypothesized that nitrogen limitation might stimulate DMSP production, because it could replace nitrogencontaining osmolytes, such as glycine betaine or proline (Turner et al 1988).…”

Compatible solutes in three marine intertidal microphytobenthic Wadden Sea diatoms exposed to different salinities

“…The first phase is a very rapid change (seconds) in turgor pressure caused by water fluxes in or out of the cells following the osmotic gradient (van Bergeijk et al, 2003), which was not considered in the present investigation. The second phase is the relatively slow change (minutes to hours) in the cellular concentrations of osmotically active solutes (osmolytes) until a new steady state is achieved.…”

“…In algae, the osmoprotectants are restricted to four major classes of solutes: sugars and polyols, free amino acids and derivates, quaternary ammonium compounds (QUARCS), and tertiary sulphonium compounds (TSCS) (Bisson & Kirst, 1995;Erdmann & Hagemann, 2001). Among the compatible solutes, proline appears to be the most widely distributed osmolyte accumulated under osmotic stress (Kirst, 1990;van Bergeijk et al, 2003;Plettner, 2002;Krell, 2006). In eukaryotes, proline is synthesized from glutamate via D 1 -pyrroline-5-carboxylate (P5C) in two successive reductions catalysed by D 1 -pyrroline-5-carboxylate synthase (P5CS) and D…”

Assessment and Characteristics of DMSP Lyase Activity in Seawater and Phytoplankton Cultures

“…DMSP is an osmolyte, but its concentration is not directly related to salinity, and phytoplankton do not quickly adjust DMSP to sudden salinity changes (Kirst, 1996;Van Bergeijk et al, 2003). In addition, since salinity is relatively constant in offshore waters, it seems unlikely that DMSP lyase enzymes are used for osmotic adjustment alone.…”