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Environmental context: Arsenic is a globally distributed element, occurring in various chemical forms with toxicities ranging from harmless to highly toxic. We examined sediment samples from Great Salt Lake, an extreme salt environment, and found a variety of organoarsenic species not previously recorded in nature. These new compounds are valuable pieces in the puzzle of how organisms detoxify arsenic, and in our understanding of the global arsenic cycle. Arsenic-containing lipids are natural products found predominantly in marine organisms. Here, we report the detection of known and new arsenolipids in sediment samples from Great Salt Lake, a hypersaline lake in Utah, USA, using high-performance liquid chromatography in combination with both elemental and molecular mass spectrometry. Sediments from four investigated sites contained appreciable quantities of arsenolipids (22–312 ng As g−1 sediment) comprising several arsenic-containing hydrocarbons and 20 new compounds shown to be analogues of phytyl 2- O -methyl dimethylarsinoyl riboside. We discuss potential sources of the detected arsenolipids and find a phytoplanktonic origin most plausible in these algal detritus-rich salt lake sediments. Environmental context. Arsenic is a globally distributed element, occurring in various chemical forms with toxicities ranging from harmless to highly toxic. We examined sediment samples from Great Salt Lake, an extreme salt environment, and found a variety of organoarsenic species not previously recorded in nature. These new compounds are valuable pieces in the puzzle of how organisms detoxify arsenic, and in our understanding of the global arsenic cycle. [ABSTRACT FROM AUTHOR]

Lipid-soluble arsenic compounds, also called arsenolipids, are ubiquitous marine natural products of currently unknown origin and function. In our search for clues about the possible biological roles of these compounds, we investigated arsenic metabolism in the unicellular green alga Dunaliella tertiolecta, and discovered an arsenolipid fundamentally different from all those previously identified; namely, a phytyl 5-dimethylarsinoyl-2- O-methyl-ribofuranoside. The discovery is of particular interest because 2- O-methylribosides have, until now, only been found in RNA. We briefly discuss the significance of the new lipid in biosynthesis and arsenic biogeochemical cycling. [ABSTRACT FROM AUTHOR]

Primary production in Mono Lake, a hypersaline soda lake rich in dissolved inorganic arsenic, is dominated by Picocystis strain ML. We set out to determine if this photoautotrophic picoplankter could metabolize inorganic arsenic and in doing so form unusual arsenolipids (e.g., arsenic bound to 2-O-methyl ribosides) as reported in other saline ecosystems and by halophilic algae. We cultivated Picocystis strain ML on a seawater-based medium with either low (37 µM) or high (1000 µM) phosphate in the presence of arsenite (400 µM), arsenate (800 µM), or without arsenic additions (ca 0.025 µM). Cultivars formed a variety of organoarsenic compounds, including a phytyl 2-O-methyl arsenosugar, depending upon the cultivation conditions and arsenic exposure. When the cells were grown at low P, the organoarsenicals they produced when exposed to both arsenite and arsenate were primarily arsenolipids (~88%) with only a modest content of water-soluble organoarsenic compounds (e.g., arsenosugars). When grown at high P, sequestration shifted to primarily water-soluble, simple methylated arsenicals such as dimethylarsinate; arsenolipids still constituted ~32% of organoarsenic incorporated into cells exposed to arsenate but < 1% when exposed to arsenite. Curiously, Picocystis strain ML grown at low P and exposed to arsenate sequestered huge amounts of arsenic into the cells accounting for 13.3% of the dry biomass; cells grown at low P and arsenite exposure sequestered much lower amounts, equivalent to 0.35% of dry biomass. Extraction of a resistant phase with trifluoroacetate recovered most of the sequestered arsenic in the form of arsenate. Uptake of arsenate into low P-cultivated cells was confirmed by X-ray fluorescence, while XANES/EXAFS spectra indicated the sequestered arsenic was retained as an inorganic iron precipitate, similar to scorodite, rather than as an As-containing macromolecule. Samples from Mono Lake demonstrated the presence of a wide variety of organoarsenic compounds, including arsenosugar phospholipids, most prevalent in zooplankton (Artemia) and phytoplankton samples, with much lower amounts detected in the bottom sediments. These observations suggest a trophic transfer of organoarsenicals from the phytoplankton (Picocystis) to the zooplankton (Artemia) community, with efficient bacterial mineralization of any lysis-released organoarsenicals back to inorganic oxyanions before they sink to the sediments. [ABSTRACT FROM AUTHOR]

The As concentrations, along with 34 other elements, and the As speciation were investigated in wild-grown samples of the parasitic mushroom Tolypocladium ophioglossoides with inductively coupled plasma mass spectrometry (ICPMS) and high performance liquid chromatography coupled to ICPMS. The As concentrations were 0.070–3.44 mg kg−1 dry mass. More remarkable was the As speciation, where up to 56% of the extracted As were found to be an unknown As species, which was marginally retained under anion- and also cation-exchange conditions. After testing several different chromatographic settings, the compound was finally isolated and identified as 2-(sulfoxyethyl) trimethylarsonium ion (in short: arsenocholine- O -sulfate) with high resolution mass spectrometry. The compound was synthesized and further quantified in all investigated samples via ion-pair chromatography coupled to ICPMS. In addition to the high abundance of arsenocholine- O -sulfate in T. ophioglossoides , small amounts of this As species were also detected in one sample of the host mushroom, Elaphomyces asperulus. In a sample of another parasitic mushroom, Ophiocordyceps sinensis , arsenocholine- O -sulfate could not be detected, but the main species was another unknown compound that was oxidized to inorganic As(V) with hydrogen peroxide. This is the first discovery of arsenocholine- O -sulfate in nature. It is possible that it is present in many other organisms, at least in low concentrations, and just has not been detected there yet because of its unusual chromatographic behavior. The existence of arsenocholine- O -sulfate brings up questions again about the biotransformation pathways of As in the environment and the specific behavior of fungi. Image 1 • Arsenocholine- O -sulfate was discovered for the first time in nature. • Arsenocholine- O -sulfate was the main As species in Tolypocladium ophioglossoides. • Concentrations of As species and 35 elements were determined in T. ophioglossoides. • Hosts, Elaphomyces spp., show different elemental profiles than T. ophioglossoides. [ABSTRACT FROM AUTHOR]