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

Abstract

Dimethylsulfoniopropionate (DMSP) is produced by a wide variety of marine phytoplankton, and it can be enzymatically cleaved to dimethylsulfide (DMS) and acrylate by DMSP lyases. DMS formation in the sea plays an important role in the global sulfur cycle, yet the factors regulating production of DMS are poorly understood. We evaluated various procedures used for in vitro assays of DMSP lyase activity (DLA) of cells captured on filters. We also compared in vitro DLA from plankton material collected from diverse water samples, as well as from cultures of different phytoplankton species. The type of filter used to collect plankton material affected the apparent in vitro DLA, with glass fiber filters (Whatman GF/F) yielding higher rates than polycarbonate filters. Treatment of filtered plankton with Tris buffer (200 mM in 500 mM NaCl), with vigorous mixing, appeared to permeablize cells allowing maximal DLA. We found that buffer pH and dithiothreitol (DTT) affected DLA positively or negatively depending on the phytoplankton species or water sample tested. In general, natural seawater plankton and cultured dinoflagellates had higher DLA with higher pH buffers (pH range 6.5 -8.5). In contrast, the prymnesiophytes Emiliania huxleyi and Phaeocystis antarctica had higher in vitro DLA at lower pH (pH range 6.5 -8.5), and DTT and Triton X-100 significantly increased the apparent enzyme activities. Not all phytoplankton contained detectable DLA, and DLA varied greatly among strains of the same species. DLA was however, detectable in all samples of particulate materials collected from a wide range of marine surface waters, including those from the coastal Gulf of Mexico, North Atlantic and Southern Ocean, and these samples showed patterns of high Chl a normalized DLA where high irradiances and low nutrients occur. Consistent with this observation, the phytoplankton cultures isolated from such environments also showed high DLA. Thus, light and nutrients may be important factors determining DLA. However, not all the variations in DLA were explained by light and nutrients, and these variations may be due to the different functions of DMSP lyases such as osmotic regulation, anti-grazing, and antioxidant activity.

Comparative functional characteristics of DMSP lyases extracted from polar and temperate Phaeocystis species

“…Thus, > 98% of the DMSP lyase activity was associated with the phytoplankton cells. This finding is consistent with previous studies that have shown that the majority of DMSP lyase activity is associated with phytoplankton size classes in seawater and phytoplankton cultures (Steinke et al 2002, Yost & Mitchelmore 2009, Harada & Kiene 2012. While some bacteria may have been attached to the Phaeocystis cells, our preliminary studies on the de novo peptide sequencing of the partially purified Phaeocystis DMSP lyases indicated lack of homology with the 6 known proteins of bacterial DMSP lyases (B. R. Mohapatra et al unpubl.…”

“…The extraction of DMSP lyase was performed as reported previously with some modifications (Harada & Kiene 2012). Briefly, algal pellets from each flask were resuspended in 5 ml of ice-cold 200 mM TrisHCl buffer (pH 7.5) containing 500 mM NaCl, 2 mM dithiothreitol (DTT) and 0.1% (v/v) Triton X-100, followed by vigorous vortex mixing and centrifugation at 3500 × g (4°C) for 15 min.…”

Salinity and growth effects on dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) cell quotas of Skeletonema costatum, Phaeocystis globosa and Heterocapsa triquetra

“…In addition, these molecules take part of an intracellular antioxidant cascade as ROS scavengers (Sunda et al, 2002). Phytoplankton cells may probably use DMSP and derivatives for different functions, they are not necessarily exclusive (Harada and Kiene, 2011). Indeed, multifunctional osmolytes like DMSP are more likely to be selected by phytoplankton species (Welsh, 2000).…”

“…4). In the late exponential phase of P. globosa and H. triquetra which possess DLA, DMSPp of senescent cells was quickly cleaved into DMS and then oxidized into DMSO whereas only DMSP can be oxidized into DMSO in DMSP-producing diatoms which do not possess DLA (Harada and Kiene, 2011). DMSP-lyase may be used to regulate DMSP concentration either for the greater efficiency of its by-products (DMS and acrylate) as antioxidants (Sunda et al, 2002) and grazing deterrents, or as a disposal of the over-accumulated DMSP for osmotic regulation and overflow mechanism (Stefels and van Leeuwe, 1998).…”

Annual cycle of dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) related to phytoplankton succession in the Southern North Sea

“…DMSP is also a source of carbon (C) and S for heterotrophic organisms (Kiene and Linn, 2000a) and acts as a chemical cue for higher trophic level organisms (Steinke et al, 2002). These physiological functions are not necessarily exclusive (Harada and Kiene, 2011) and phytoplankton cells may use several of them.…”