Characteristics of DMSP-lyase in Phaeocystis sp. (Prymnesiophyceae)

Abstract

The marine phytoplankton species Phaeocystis sp. is one of the few microalgae known to be able to convert dimethylsulfoniopropionate (DMSP) enzymatically into dimethyl sulfide (DMS) and acrylic acid. The function of this enzymatic process for the organism is not known. From experiments with crude extracts and whole cells of axenic cultures of Phaeocystis it was concluded that DMSP-lyase is membrane-bound and located extracellularly because: (1) the enzyme activity in extracts and in whole cells varied in a simllar manner with pH; (2) between 50 and 80% of the DhdSPlyase activity was associated w~t h the membrane fraction, (3) lyase activity in whole cells was inhibited by the nonpermeable thiol-reagent p-chloromercuribenzenesulfonic acid @CMBS). The pH optimum was 10.5 or higher, which is in contrast with available data for the enzyme from other organisms. The pH profile, the requirement for reduced thiol groups in extracts and the inhibition by pCMBS suggest the involvement of cysteine residues a t the active site. Production of DMSP as well as its cleavage by DMSP-lyase are apparently not involved in the short term regulation of the osmot~c potential of cells upon changes in salinity.

Environmental constraints on the production and removal of the climatically active gas dimethylsulphide (DMS) and implications for ecosystem modelling

“…This is particularly relevant for organisms with a thick boundary layer such as Phaeocystis colonies. The idea of such a role for DMSP-lyase was instigated by the observations that Phaeocystis exhibits high in vivo lyase activities when dissolved DMSP is added to the culture medium and that extracellular inhibitors can repress this activity (Stefels and Dijkhuizen 1996). In addition, it has been observed that acrylate, one of the products of DMSP degradation, accumulates in the mucus layer of Phaeocystis colonies (Noordkamp et al 2000), which is in agreement with an extracellular location of the enzyme.…”

Production and consumption of dimethylsulfide (DMS) in North Atlantic waters

“…The cleavage of DMSP to DMS and acrylate is accomplished enzymatically via DMSP-lyase which has been shown to exist in marine bacteria , de Souza & Yoch 1995a, Yoch et al 1997. There are also a few species of phytoplankton which are known to possess DMSPlyase (Stefels & Dijkhuizen 1996, Steinke et al 1998, and it is speculated that there may be others. The relative contribution of phytoplankton to marine DMS production is presently unknown, but may be significant in regions where DMSP-lyase-containing algal species are abundant.…”

Dynamics of dimethylsulphoniopropionate and dimethylsulphide under different CO<sub>2</sub> concentrations during a mesocosm experiment

“…Once in solution, DMSP can be utilized by many bacteria as a sulfur, carbon or energy source via catabolic demethylation to 3-methylmercaptopropionate and 3-mercaptopropionate (Kiene and Linn, 2000;Howard et al, 2006). Bacteria have also been shown to enzymatically cleave DMSP to DMS and acrylate (Kiene, 1993;Ledyard and Dacey, 1996;Stefels and Dijkhuizen, 1996;Steinke and Kirst, 1996) and novel evidence suggests DMSP-dependent DMS-production without the release of acrylate (Todd et al, 2007). DMS can be used as a metabolite by bacteria (Vila-Costa et al, 2006), photochemically degraded at the sea surface (Brimblecombe and Shooter, 1986;Kieber et al, 1996), or transferred to the atmosphere (Liss and Slater, 1974).…”