CSIRO PUBLISHING Environ. Chem. 2019, 16, 303–311 Rapid Communication https://doi.org/10.1071/EN19135

Origin of arsenolipids in sediments from Great Salt Lake

Ronald A. Glabonjat, A,D Georg Raber,A Kenneth B. Jensen,A Florence Schubotz,B Eric S. Boyd C and Kevin A. FrancesconiA

AInstitute of Chemistry, NAWI Graz, University of Graz, 8010 Graz, Austria. BMARUM – Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, 28359 Bremen, Germany. CDepartment of Microbiology and Immunology, Montana State University, Bozeman, MT 59717, USA. DCorresponding author. Email: [email protected]

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. 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 g1 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.

Received 10 May 2019, accepted 17 June 2019, published online 19 July 2019

Lipid-soluble arsenic compounds (arsenolipids) are natural environments rich in these two life forms. Here, we report an products found in many marine organisms. They contain arsenic investigation using high-performance liquid chromatography bound into common lipids such as fatty acids (Rumpler et al. (HPLC)–mass spectrometry to examine the arsenolipid content 2008; Sele et al. 2014), hydrocarbons (Taleshi et al. 2008; Sele in sediments from Great Salt Lake (GSL), Utah, USA. Archaea et al. 2014), fatty alcohols (Amayo et al. 2013) and phospholi- are abundant components of GSL sediments (Tenchov et al. pids (Garcı´a-Salgado et al. 2012; Viczek et al. 2016; Yu et al. 2006; Boyd et al. 2017) and abundant halophilic algae, including 2018). An intriguing addition to natural arsenolipids was Dunaliella species, have also been reported (Stephens 1973; recently found in the marine microalga Dunaliella tertiolecta Brock 1975; Meuser et al. 2013). (Glabonjat et al. 2017). This organism contained an Surface sediments (0–2 cm) were sampled from the GSL on arsenosugar-phytol in which the arsenic is bound to a 2-O- 7–14 November 2010 from four locations (Fig. 1): GSL1, methyl ribose moiety. A methoxy group in the 2-O-position of North Basin; GSL2, Gunnison Island; GSL3, South Shore; and the ribose ring is a configuration found in major classes of GSL4, Farmington Bay. Details of the collection, storage and ribonucleic acid (RNA) (Poole et al. 2000; Birkedal et al. 2015), preparation of the samples are reported in Boyd et al. (2017) but has never before been reported for simple carbohydrates, an and further details relevant to the analyses in the current study observation relevant to the hypothesised evolutionary link are presented in the Supplementary Material. In brief, the between RNA and DNA in early life’s ancient metabolism lipids were extracted from lyophilised sediments by a modified (Poole et al. 2000; Rana and Ankri 2016; Glabonjat et al. 2017). Bligh and Dyer method using a mixture of dichloromethane/ A second interesting aspect of the new arsenolipid is the ether- methanol/aqueous buffer (2 phosphate buffer at pH 7.2; and bound phytyl group. Such ether linkages to isoprenoid hydro- 2 trichloroacetic acid at pH 2.0). The dry extracts were carbons are characteristic for membrane lipids of Archaea; stored at 20 8C, and later redissolved in absolute ethanol however, similar phytyl moieties are also found attached to (300 mL) before analysis by using HPLC-elemental mass chlorophylls anchoring them to the chloroplast membrane in spectrometry (inductively coupled plasma mass spectrometry, photoautotrophs, including phytoplankton. ICPMS), and HPLC-electrospray ionisation high-resolution Guided by these two observations, we hypothesised that the mass spectrometry (HR-ESMS), following the method of new arsenosugar-phytol could be produced by planktonic algae Glabonjatetal.(2018). An aliquot of the total lipid extract or Archaea and might therefore be abundant in extreme wasanalysedonaBrukermaXisPlus ultra-high-resolution

Journal Compilation CSIRO 2019 Open Access CC BY-NC-ND303 www.publish.csiro.au/journals/env R. A. Glabonjat et al.

GSL2

GSL1 GSL4

GSL3

Fig. 1. Sediment sampling sites in Great Salt Lake (GSL) for the determination of arsenolipids (from Google Earth, accessed on 20 September 2018).

quadrupole time-of-flight mass spectrometer coupled to a in the present study are shown in Table S2 (Supplementary Dionex Ultimate 3000RS ultra-high-performance liquid chro- Material); in all cases, the obtained molecular mass agreed with matography system with an electrospray ionisation source the calculated value to within 2 ppm or less. after Woermer et al. (2013). The longest side chain we found in GSL sediments was All four sediment samples from GSL showed the presence equivalent to a phytyl moiety. A likely biosynthetic pathway of lipid-soluble arsenic (22–312 ng As g1 extracted sediment) towards the corresponding arsenolipid compound 12 was pro- comprising many arsenolipids (Table 1 and Fig. 2). Five known posed by Glabonjat et al. (2018), and comprises the substitution (1–5) and three newly discovered (6–8) arsenic hydrocarbons of methionine by dimethylarsinous acid in S-adenolsylmethio- (AsHCs), the main ones being the frequently reported AsHC332 nine, followed by 2-O-methylation of the riboside by methio- (1) and AsHC360 (3), were present in all samples (see Fig. S1 in nine, hydrolytic adenine removal, and finally, condensation of the Supplementary Material for structures of the eight AsHCs the 2-O-methylriboside with phytyl diphosphate. Shorter side found). The major arsenolipids, however, comprised a group of chains could be explained by v-hydroxylation with subsequent 21 ether terpenoids containing an arsenosugar moiety, of which alcohol oxidation to the corresponding aldehyde (both interme- only one (phytyl 2-O-methylriboside 12) has previously been diate products were detected in GSL samples; Figs 3–5 and reported (Glabonjat et al. 2017; Glabonjat et al. 2018). Struc- Fig. S4, Supplementary Material) and finally to carboxylic acid tures for these compounds were assigned based on their mass as previously described for phytanic acid (Xu et al. 2006). This spectral data as described below, and with analogy to naturally v-terminal carboxylated isoprenoid can then undergo a-or occurring non-arsenic terpenoids. b-oxidation (Jansen and Wanders 2006; Watkins et al. 2010), The various compounds separated well during chromato- as typically found in phytol degradation pathways (Fig. 6), graphy (Fig. 3 and Fig. S2, Supplementary Material). They resulting in shorter-C-chain products (e.g. pristanal, pristanic produced fragmentation patterns homologous to the pattern acid, phytone), which were also present in the sediment samples obtained for 12 (Fig. 4, Fig. S3 and Table S1, Supplementary from GSL (Figs 3–5). Material). In conjunction with the measured masses of the Quantification of arsenolipids can be performed when protonated molecular ions, [M þ H]þ, the various compounds ICPMS is used as the detector for HPLC, but only when the could be assigned distinct molecular formulae. These data compounds have been adequately separated. When many strongly indicated the presence of similar isoprenoyl 2-O-methyl- arsenolipids are present, as in these sediment samples, it is not riboside moieties in 12 of the newly discovered arsenolipids; for possible to confidently quantify the individual compounds. another eight isoprenoyl compounds, the data corresponded to a Nevertheless, we were able to estimate that in the four sediment non-methylated ‘normal’ riboside moiety. Although the identities samples, compound 12, the phytyl 2-O-methyl arsenoriboside of the lipophilic portions of the molecules could not be estab- previously found in D. tertiolecta, accounted for 5–20 % of the lished by mass spectrometry, likely structures can be proposed total arsenolipids present. Despite traces of arsenic eluting in the (Fig. 5) based on naturally occurring non-arsenic lipids and what region of arsenosugar phospholipids, neither these compounds is known of phytol metabolism (Fig. 6) in aquatic systems nor their possible O-methyl-analogues could be detected by (Rontani and Volkman 2003; Sturt et al. 2004; Rontani and means of accurate mass measurements. The absence of these Bonin 2011). The mass spectral data for all compounds identified compounds in GSL sediment extracts can be explained by rapid

304 Arsenolipids in sediments from Great Salt Lake

Table 1. Sampling sites, amounts of sediment extracted and arsenolipid concentrations detected in lipid extracts from Great Salt Lake (GSL) habitats Concentrations determined by ICPMS are typed in bold, whereas italic type values were determined by HR-ESMS and represent an estimated concentration based on relative signal intensities of individual species (concentrations are given as ng As g1 sediment; n ¼ 1)

GSL1 GSL2 GSL3 GSL4 North Basin Gunnison Island South Shore Farmington Bay

Sediment extracted (g) 21 21 49 35 Total arsenolipids 312 43 22 50 1 (AsHC332) 1.1 0.1 1.9 1.9 1.0A 0.1A 1.7A 0.9A 2 (AsHC346) ,0.1 ,0.1 ,0.1 0.1–0.2 3 (AsHC360) 4.4 1.2 0.9 2.6 4.0A 1.1A 0.9A 2.8A 4 (AsHC388) ,0.1 ,0.1 ,0.1 0.1–0.2 5 (AsHC404) ,0.1 ,0.1 ,0.1 0.1–0.2 6 (AsHC406) ,0.1 ,0.1 ,0.1 0.1–0.2 7 (AsHC408) ,0.1 ,0.1 ,0.1 0.1–0.2 8 (AsHC410) ,0.1 ,0.1 ,0.1 0.3 9 35 8 2 2 10 3 ,11,1 11 25 4 1 4 12 65.4 2.8 2.8 2.3 75 3 6 1 13 2 ,1 ,1 ,1 14 1 ,1 ,12 15 2 ,1 ,1 ,1 16 1 ,1 ,1 ,1 17 1 ,1 ,1 ,1 18 4 ,1 ,1 ,1 19 ,1 ,1 ,1 ,1 20 45 9 2 13 21 2 ,1 ,1 ,1 22 21 4 ,15 23 42,14 24 77 8 3 7 25 ,1 ,1 ,15 26 5 ,1 ,1 ,1 27 4 ,1 ,11 28 ,1 ,1 ,1 ,1 29 ,1 ,1 ,1 ,1

AConcentrations based on external calibration with standard compounds AsHC332 and AsHC360 using HR-ESMS (for other arsenolipids, no standards were available). degradation of arsenosugar phospholipids in microbial-rich detritus derived from unicellular algae inhabiting the overlaying sediment environments (Glabonjat et al. 2019). In the four water column (Meuser et al. 2013). The arsenolipid abundance GSL sediment samples, we determined concentrations of three in the sediments with ether linkages and C20 isoprenoidal major arsenolipids – two hydrocarbons, 1 (0.1–1.9 ng g1) and hydrocarbon units intuitively suggest an archaeal origin because 3 (0.9–4.4 ng g1), and the phytyl 2-O-methylriboside, 12 (2.3– archaeal membrane lipids are composed of glycerol ethers and 65.4 ng g1) – based on reversed phase (RP) HPLC-ICPMS isoprenoids (Kates 1993; Angelini et al. 2012). The ether data. The two arsenic hydrocarbons, 1 and 3, were also quanti- linkages of Archaea impart greater stability to the lipids com- fied by means of RP-HPLC-HR-ESMS, after external calibra- pared with glycerol esters and fatty acids, which are the major tion with standard compounds (Table 1). Furthermore, we components of membrane lipids in Bacteria and Eukarya. In estimated the concentrations of all 21 arsenosugar terpenoids hypersaline environments, archaeal lipid contribution increases (9–29) and eight arsenic hydrocarbons (1–8) detected in the with increasing salinity (Tenchov et al. 2006), and GSL sedi- present study using the obtained HR-ESMS data based on the ments have been shown to host plentiful and diverse Archaea assumption that related compounds give a similar ESMS (Boyd et al. 2017; Baxter 2018). However, one of the major response (Table 1). arsenolipids in the sediments, the phytol derivative 12, has We hypothesise the origin of the arsenolipids in these GSL recently been identified in the unicellular alga D. tertiolecta sediments to be either halophilic Archaea or algae in the form of (Glabonjat et al. 2017), and Dunaliella species have been

305 R. A. Glabonjat et al.

1 (AsHC332) 3 (AsHC360) (AsPL958) AsFAs 50 000 Arsenolipid 40 000 standards 12 30 000

20 000 (AsHC444)

10 000

0 30 000 Great Salt Lake 1 North Basin 20 000

10 000

0

4000 Great Salt Lake 2 Gunnison Island 3000 75 (counts)

z 2000 / m 1000

Signal 0

4000 Great Salt Lake 3 South Shore 3000

2000

1000

0

4000 Great Salt Lake 4 Farmington Bay 3000

2000

1000

0 0 5 10 15 20 25 30 35 Retention time (min)

Fig. 2. RP-HPLC-ICPMS chromatograms of arsenolipid standards (three arsenic fatty acids (AsFAs) and three AsHCs), and lipid extracts of sediments from four Great Salt Lake samples (retention times of AsPL958 and phytyl 2-O-methylriboside (12) from certified reference material Hijiki and D. tertiolecta extracts respectively are also indicated). Asahipak ODP-50 (4.6 125 mm, 5 mm; Shodex); 40 8C; 20 mL injection volume; flow rate 0.5 mL min1; mobile phase A: 0.1 % formic acid in water, B: 0.1 % formic acid in EtOH; gradient: 0–1 min, 30 % B; 1–30 min, 30–100 % B; 30–32 min, 100 % B; 32–32.1 min, 100–30 % B; 32.1– 40 min, 30 % B; flow split post column: 20 % to ICPMS; support flow 1 % formic acid in water at 0.5 mL min1; gradient compensation 20 % EtOH in water. reported as abundant planktonic organisms in the overlaying from Dunaliella species therefore represents an important water body of the GSL (Stephens 1973; Stephens and Gillespie source of organic material continuously depositing on the lake 1976; Meuser et al. 2013). Planktonic detritus, including detritus bottom.

306 Arsenolipids in sediments from Great Salt Lake

m/z 361.2446 m/z 333.2133 C19H42OAs C H OAs 17 38 2 (AsHC360) 1 (AsHC332)

m/z 493.2872

C24H50O5As 24

0 5 10 15 20 25 30 35

m/z 507.3028

C25H52O5As 25

m/z 521.3187

C26H54O5As

z 20 / m

m/z 547.3338

C28H56O5As 12

Signals at corresponding m/z 549.3494

C28H58O5As 11

m/z 563.3289

C28H56O6As 9

m/z 533.3181

C27H54O5As 17

m/z 535.3338

C27H56O5As 15

0 5 10 15 20 25 30 35 Retention time (min)

Fig. 3. RP-HPLC-HR-ESMS chromatograms of the major arsenolipids present in Great Salt Lake sample 1 (GSL1). A complete list with chromatograms of all 29 arsenolipids determined in GSL sediments is presented in Fig. S2 (Supplementary Material). HPLC conditions: Asahipak ODP-50 (4.6 125 mm, 5 mm); 40 8C; 5 mL injection volume; flow rate 0.5 mL min1; mobile phase A: 0.1 % formic acid in water, B: 0.1 % formic acid in EtOH; gradient: 0–1 min, 30 % B; 1–30 min, 30–100 % B; 30–32 min, 100 % B; 32–32.1 min, 100–30 % B; 32.1–40 min, 30 % B.

To provide further clues about the primary source of characteristic of unicellular algae (e.g. chloroplast lipids and arsenolipids identified in the sediments, we determined the betaine lipids) (Dembitsky 1996) were one to four orders profile of normal lipids in the same sediment extracts. of magnitude more abundant (Table S3, Supplementary Although archaeal lipids were present in GSL sediments, lipids Material). Furthermore, the archaeal lipids in the sediments

307 R. A. Glabonjat et al.

251.03 237.01

–H2O –H2O O 176.99 269.04 O 164.99 255.02 CH CH3 3 –H O –CH O H C 2 H3C 2 3 As 195.00 As 195.00 111.04 97.03 O O 122.98 O 122.98 O –H O –H O 2 R 2 R 104.97 104.97

138.97 138.97 HO OCH3 HO OH –H2 –H2 136.99 136.99

111.0446 100 m/z 493.2872 (Δm = 0.7 ppm)

50 104.9686 C24H50O5As 68.0266 122.9790 83.0499 195.0001 24 138.9737 176.9893 0 111.0446 100 m/z 507.3028 (Δm = 0.6 ppm) C H O As 50 104.9687 25 52 5 68.0266 122.9788 83.0500 195.0001 25 138.9737 176.9898 0 111.0446 100 m/z 521.3187 (Δm = 1.1 ppm)

C26H54O5As 50 104.9686 20 68.0266 122.9790 83.0500 195.0001 138.9739 176.9896 224.0984 250.0958 288.3829 0 111.0446 100 m/z 547.3338 (Δm = 0.1 ppm)

C28H56O5As 50 104.9686 195.0001 12 68.0266 83.0500 122.9790 138.9740 176.9900 251.0252 269.0360 0 111.0446 100 m/z 549.3494 (Δm = 0.1 ppm)

C28H58O5As 50 104.9686 11 68.0266 83.0499 122.9789 195.0001

Relative abundanceRelative (%) 138.9739 176.9892 251.0274 0 111.0447 100 m/z 563.3289 (Δm = 0.4 ppm)

C28H56O6As 50 104.9687 122.9790 9 68.0266 83.0500 136.9946 164.9897 195.0002 251.0263 284.6209 0 97.0291 100 55.0552 m/z 533.3181 (Δm = 0.1 ppm)

C27H54O5As 50 81.0707 195.0002 17 69.0708 104.9685 138.9741 164.9895 214.6744 237.0111 255.0218 0 97.0291 100 m/z 535.3338 (Δm = 0.1 ppm)

C27H56O5As 50 195.0001 15 104.9687 138.9737 57.0709 84.0451 164.9894 219.0009 237.0113 0 60 80 100 120 140 160 180 200 220 240 260 280 300 m/z

Fig. 4. Proposed fragmentation and tandem mass spectra of the eight major naturally occurring arsenolipids including the phytyl 2-O-methylriboside (12) and seven structurally similar compounds present in Great Salt Lake sample 1 (GSL1). The given m/z values are for [M þ H]þ precursor ions used for fragmentation at a normalised collision energy of 50. Fig. S3 (Supplementary Material) shows the MS/MS spectra of all 29 arsenolipids determined in GSL sediment extracts. Table S1 (Supplementary Material) provides an overview on the proposed fragments in their protonated forms. contained a significant proportion (10–18 %) of extended hydrocarbons with 20 carbons or less, and arsenic analogues of phytyl chains, i.e. isoprenoid hydrocarbons with 25 carbons, archaeal lipids with isoprenoid hydrocarbons of 25 carbons which are characteristic for halophilic Archaea (Fig. S5, were not found among the arsenolipids. We therefore find it Supplementary Material) (Angelini et al. 2012). Notably, the more likely that the isoprenoidal arsenolipids, and other arsenolipids in GSL sediments contained only isoprenoidal arsenolipids, in GSL sediments are primarily derived from

308 Arsenolipids in sediments from Great Salt Lake

9 10 O CH O CH O 3 C H AsO 3 C H AsO CH H3C 28 55 6 H3C 28 53 6 H C 3 As As 3 As O O O O O O CH3 C20H39O C20H37O 22 C H AsO CH CH CH 25 51 5 O O CH HO O CH CH 3 3 3 CH HO 3 3 HO O 3 H C 3 3 As O O CH3 O CH H3C 3 11 As O O C28H57AsO5 CH3 CH3 CH3 CH3 CH 23 HO O CH3 3 C25H51AsO5 CH3 CH3 CH3 O CH HO OH H C 3 3 As O O CH3 12 (AsSugPhytol) O CH CH CH CH CH3 3 3 3 3 C28H55AsO5 H C HO O CH3 3 As O O 24 CH3 C H AsO CH CH CH 24 49 5 O 13 O 14 CH 3 3 3 CH3 CH3 HO O 3 H3C C H AsO H C C H AsO As 27 53 6 3 As 27 53 6 O O O CH3 O O H3C As C20H39O C19H37O O O CH 3 25 O HO OH HO O CH3 CH C24H49AsO5 H C 3 CH3 CH3 CH3 3 As HO OH O O CH 3 15

C27H55AsO5 CH3 CH3 CH3 O HO O CH3 CH H C 3 3 As O O CH3 O CH3 H3C As 26 C H AsO O O 23 47 5 CH3 CH3 CH3 CH3 16 HO O CH3 C H AsO CH CH CH CH 27 55 5 O CH 3 3 3 3 H C 3 HO OH 3 As O O CH O H C 3 27 3 As CH3 C H AsO O 23 47 5 O CH CH3 CH3 CH3 3 17 HO OH

C27H53AsO5 CH3 CH3 CH3 CH3 HO OH O CH3 H3C As O O 18 O 19 O CH3 CH3 CH3 28 H3C C H AsO H3C C26H51AsO6 As 26 53 6 As C H AsO O O CH CH 22 45 5 O O HO O CH 3 3 C H O C H O 3 18 37 19 37 O CH3 H3C HO O CH3 HO OH As O O CH3 O CH H3C As 3 29 O C H AsO O 22 45 5 CH3 CH3 CH3 CH3 20 HO OH C26H53AsO5 CH3 CH3 CH3 HO O CH3

O CH H C 3 3 As O O CH3 21 C26H51AsO5 CH3 CH3 CH3 HO O CH3

Fig. 5. All 21 arsenosugar terpenoids found in Great Salt Lake sediment extracts. The structure of 12 (C28H55AsO5) was previously elucidated in D. tertiolecta (Glabonjat et al. 2017). The remaining structures were proposed based on comparison of mass spectral properties with those of 12, and

structural similarities to non-arsenic-containing microbial lipids. Particularly the unsaturated phytyl 2-O-methylriboside analogue 11 (C28H57AsO5) and its non-methylated ribose analogues 16 and 17 (C27H55AsO5 and C27H53AsO5) are biochemically very likely. For the remaining molecules, we show only one possible isomer of the lipophilic side chain, and for 9, 10, 13, 14, 18 and 19, a multitude of possible side chain structures (alcohols, aldehydes, esters, ketones, etc.) are possible (Fig. S4, Supplementary Material). halophilic algae such as Dunaliella spp. (Glabonjat et al. 2017). to elevated environmental arsenic concentrations or if the This interpretation is consistent with the suggestion by arsenolipids serve other purposes in these organisms remains Rosenberg (1967) that galactolipids, necessary for full photo- to be determined. However, As is elevated in GSL, with recent synthetic activity, form hydrophobic complexes through inter- studies reporting a mean annual concentration of 112 mgL1 in actions of their double bonds with isoprenoid methyl groups filtered water from 24 sites sampled over a 14-year period in chlorophylls, carotenes and quinones, and thereby ensure (Adams et al. 2015). Little variation in As concentrations was appropriate spacing and molecular orientation necessary for noted across sites, although a slight seasonal variation of As photosynthetic reactions. concentration was noted. This suggests that the organisms Whether the presence of the isoprenoid arsenolipids in these sampled in the present study were likely exposed to similar unicellular halotolerant algae reflects a detoxification response amounts of As. Further work is required to evaluate potential

309 R. A. Glabonjat et al.

CH3 R

CH3 CH3 CH3 CH3 Phytane

+ 2H

CH3 R CH3 R CH 3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 Phytene 1) +2H Pristane –CH 2 2) –C2H4

R CH3

CH3 CH3 CH3 CH3 Phytol ω-hydroxylation

OH R

CH3 CH3 CH3 CH3

alcohol oxidation

R COOH

CH3 CH3 CH3 CH3 R = arsenosugar moiety α-and/or β-oxidation

R COOH

CH3 CH3 CH3

Fig. 6. Proposed pathways for the biotransformation of phytyl-arsenoribosides to the corresponding pristane

and phytane analogues in saline environments (adapted from Rontani and Bonin (2011) where R ¼ OH or CH3), and by v-hydroxylation and subsequent alcohol oxidation to the corresponding carboxylic acid, which can finally undergo a-orb-oxidation as previously described for phytanic acid (adapted from Jansen and Wanders (2006); Xu et al. (2006); Watkins et al. (2010) where R ¼ OH). links between the prevalence of arsenolipids in GSL sediments in GSL sediment extracts; Fig. S3 shows high resolution frag- or waters and the availability of As. mentation spectra of all 29 detected arsenolipids; Fig. S4 gives an In summary, we identified 29 arsenolipids including 23 new overview on possible oxidised arsenosugar lipids; and Fig. S5 compounds in sediments from GSL, a hypersaline lake, thereby shows examples of detected ‘normal’ archaeal lipids determined demonstrating the widespread abundance of arsenolipids, which in the GSL sediment extracts in this study. were hitherto thought to be limited to marine ecosystems. Most of the new arsenic compounds contain isoprenoid chains and an Conflicts of interest ether bond, which are characteristics of membrane lipids from The authors declare no conflicts of interest. Archaea. Nevertheless, here we suggest that the primary source of the various arsenolipids in GSL sediments is most likely sedimented detritus of halotolerant phytoplankton, with only a Acknowledgements minor contribution from the microbial community inhabiting This research was supported by the Austrian Science Fund (FWF) project the benthic sediments themselves. number I2412-B21. We also thank NAWI Graz for supporting the Graz Central Laboratory – Environmental Metabolomics. Florence Schubotz Supplementary material acknowledges funding from the Central Research Development Fund of the University of Bremen. Eric Boyd acknowledges funding from the NASA The supplementary material contains further details about sample Astrobiology Institute (project no. NNA15BB02A). The authors are grateful collection, preparation and determination. Table S1 shows pro- to David Naftz and Mark Marvin-DiPasquale for sample collection. posed MS/MS fragmentation products of arsenosugar isoprenoids present in GSL sediment extracts; Table S2 provides details on References high resolution mass spectral data of all the 29 detected arseno- Adams WJ, DeForest DK, Tear LM, Payne K, Brix KV (2015). Long-term lipids; Table S3 gives an overview on ‘normal’ (arsenic-free) monitoring of arsenic, copper, selenium, and other elements in Great Salt membrane lipids present in the GSL sediment extracts; Fig. S1 Lake (Utah, USA) surface water, brine shrimp, and brine flies. Environ- shows structures of the eight detected AsHCs; Fig. S2 shows RP- mental Monitoring and Assessment 187, 118. doi:10.1007/S10661-014- HPLC-HR-ESMS chromatograms of all 29 arsenolipids detected 4231-6

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