Effect of acidification on preservation of DMSP in seawater and phytoplankton cultures: Evidence for rapid loss and cleavage of DMSP in samples containing Phaeocystis sp. Daniela A. del Valle a,b, ⁎, Doris Slezak a,b,c , Casey M. Smith a,b , Alison N. Rellinger a,b , David J. Kieber d , Ronald P. Kiene a,b a Department of Marine Sciences, University of South Alabama, Mobile, AL 36688, USA b Dauphin Island Sea Lab, Dauphin Island, AL, 36528, USA c Department of Molecular Biology, University of Salzburg, 5020 Salzburg, Austria d Department of Chemistry, State University of New York, College of Environmental Science and Forestry, Syracuse, NY 13210, USA abstract article info Article history: Received 27 March 2010 Received in revised form 24 September 2010 Accepted 8 December 2010 Available online 15 December 2010 Keywords: Dimethylsulfoniopropionate Dimethylsulfide DMSP DMS DMSP lyase Emiliania huxleyi Phaeocystis The algal metabolite, dimethylsulfoniopropionate (DMSP), is known to be stable in acid solution and acidification of seawater samples to pH b 2 has been used previously to preserve samples for DMSP analysis. We, however, observed substantial (60–94%) DMSP losses in acidified seawater samples from a colonial Phaeocystis antarctica bloom in the Ross Sea, Antarctica, whereas little or no loss of DMSP occurred in other waters where Phaeocystis spp. were minor components of the phytoplankton community. Tests with cultures of colonial P. globosa showed that up to 68% of culture DMSP was lost during the first minutes after acid addition. After initial losses, DMSP remained constant, confirming the chemical stability of DMSP at pH b 2. Biological factors must therefore play a role in the initial acid-mediated DMSP loss in cultures or seawater. Dimethylsulfide (DMS) was produced immediately after acidification of P. globosa cultures suggesting that DMSP was degraded via lyase enzymes. Major acid-mediated DMSP losses were unique to colonial Phaeocystis spp., as no significant DMSP losses occurred with solitary P. globosa cells or other phytoplankton genera tested, although a small amount of DMS production (equivalent to b 3% of culture DMSP) was observed after acidification of a high DMSP lyase strain of Emiliania huxleyi (CCMP 373). Exogenous dissolved 35 S-DMSP was not lost during acidification of colonial P. globosa cultures indicating that intracellular rather than dissolved DMSP was cleaved during the time between acid addition and lyase enzyme inactivation. Experiments with the differentially-permeable DMSP lyase inhibitors, p-CMB and p-CMBS, showed that only the membrane permeable p-CMB stopped DMSP loss under acidified conditions, confirming that DMSP loss occurred intracellularly. These results highlight the remarkable potential activity of DMSP lyases in Phaeocystis spp. and suggest that acidification alone is inadequate for preservation of samples containing colonial Phaeocystis spp. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Dimethylsulfoniopropionate (DMSP; (CH 3 ) 2 S + CH 2 CH 2 COO - ) is an osmolyte and potential anti-stress compound produced in large amounts by a wide variety of marine phytoplankton and macroalgae (Keller et al., 1989; Stefels, 2000). The particulate pool of DMSP in seawater generally ranges from 10 to 100 nM in surface waters but even higher concentrations (200–1000 nM) can occur during major phytoplankton blooms (van Duyl et al., 1998). The biogeochemistry and physiological chemistry of DMSP are subjects of intense study, in part because DMSP contributes significantly to carbon and sulfur cycling within the microbial food web (Kiene et al., 2000; Simó et al., 2009), and may function as an antioxidant within phytoplankton cells (Sunda et al., 2002) and as a signaling compound (Fredrickson and Strom, 2009; Seymour et al., 2010). DMSP is also the principal precursor of dimethylsulfide (DMS), a volatile sulfur species that annually transfers between 0.5 and 1.0 Tmol of sulfur from the oceans to the atmosphere (Kettle and Andreae, 2000). Sea-air exchange of DMS affects the atmosphere in many important ways, particularly by serving as a source of acidic aerosol particles that scatter sunlight and contribute to formation and/or growth of cloud condensation nuclei (Ayers and Gillett, 2000; von Glasow, 2007). DMS derived aerosols can affect solar radiation reaching the Earth's surface leading to the possibility that biological DMS production could be involved in a feedback loop modulating regional and global climate (Charlson et al., 1987). Testing of such a Marine Chemistry 124 (2011) 57–67 ⁎ Corresponding author. Department of Oceanography, University of Hawaii, 1000 Pope Road, Honolulu, HI 96822, USA and Center for Microbial Oceanography: Research and Education, Honolulu, HI 96822, USA. Tel.: +1 808 956 0308; fax: +1 808 956 0300. E-mail address: dadv@hawaii.edu (D.A. del Valle). 0304-4203/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.marchem.2010.12.002 Contents lists available at ScienceDirect Marine Chemistry journal homepage: www.elsevier.com/locate/marchem