Rapid Biotransformation of Arsenate into Oxo-Arsenosugars by a Freshwater Unicellular Green Alga,Chlamydomonas reinhardtii

Abstract

We examined the short-term metabolic processes of arsenate for 24 h in a freshwater unicellular green alga, Chlamydomonas reinhardtii wild-type strain CC-125. The arsenic species in the algal extracts were identified by high-performance liquid chromatography/inductively coupled plasma mass spectrometry after water extraction using a sonicator. Speciation analyses of arsenic showed that the levels of arsenite, arsenate, and methylarsonic acid in the cells rapidly increased for 30 min to 1 h, and those of dimethylarsinic acid and oxo-arsenosugar-glycerol also tended to increase continuously for 24 h, while that of oxo-arsenosugar-phosphate was quite low and fluctuated throughout the experiment. These results indicate that this alga can rapidly biotransform arsenate into oxo-arsenosugar-glycerol for at least 10 min and then oxo-arsenosugar-phosphate through both reduction of incorporated arsenate to arsenite and methylation of arsenite and/or arsenate retained in the cells to dimethylarsinic acid via methylarsonic acid as an possible intermediate.

Potential of macrophyte for removing arsenic from aqueous solution

“…In other pteridophytes, however, exposure to As resulted in increased chlorophyll and carotenoid production, in Pteris vittata, and a decrease in the content of these pigments in Pteris ensiformis (Sing et al, 2006). In the biotransformation test, the chlorophyll Potential of macrophyte for removing arsenic from aqueous solution contents of Chlamydomonas reinhardtii cells were reduced to zero in the presence of As (V), indicating that such cells were unable to grow under ≥ 0.5 mM after 12 h exposure (Miyashita et al, 2011).…”

Cyanobacteria produce arsenosugars

“…The cells were solubilised as described previously. [24] Briefly, the cells were predigested in the presence of conc. HNO 3 , and then completely solubilised in a closed-vessel microwave digestion system (speedwave MWS-3 þ ; Berghof) after addition of hydrogen peroxide.…”

“…Total As analysis was accomplished by inductively coupled plasma-mass spectrometry (ICP-MS, ELAN DRC-e; PerkinElmer SCIEX Inc., Concord, Canada) following previously reported procedures. [24] The following ICP-MS conditions were applied for specific determination of As (as AsO þ at m/z 91) and zirconium (as ZrO þ at m/z 106): RF power, 1600 W; nebuliser gas flow, 1.05 L min À1 ; auxiliary gas flow, 1.4 L min À1 ; plasma gas flow, 18 L min À1 ; cell gas flow, 0.7 mL min À1 oxygen (purity: 99.999 %); rejection parameter a (RPa), 0; rejection parameter q (RPq), 0.25 (ZrO þ ) and 0.55 (AsO þ ); axial field voltage, 250 V. Dynamic reaction cell (DRC) mode was used for the speciation analysis as well as total As analysis. Both analyses were performed, after optimisation of the oxygen gas flow rate into the cell.…”

“…Extraction and identification of the As compounds formed by the two cyanobacteria Biotransformation of incorporated As V in the cyanobacterial cells exposed to As V at the concentrations selected by the As toxicity test was confirmed by analyses of water-soluble As metabolites by using a combined ICP-MS and highperformance liquid chromatography (HPLC) system (HPLC-ICP-MS) after the following extraction procedures. The cells collected as described above in the As V uptake section were freeze-dried, [24] because removing water completely was necessary for the following extraction carried out with a small precise amount (1 mL) of water. Each suspension in water was then homogenised on ice with a sonicator for 30 s at a power level of 50 W. This process was repeated six times with cooling intervals of 60 s between each sonication until almost all the cells were disrupted as observed by light microscopy.…”

“…[18][19][20] Thus, identification of As metabolites in microbes grown in pure culture, such as eukaryotic microalgae and prokaryotic cyanobacteria, has been performed to confirm biotransformation mechanisms of As after experimental exposure to inorganic As species. Previous reports generally indicate that microalgae (not only marine species (Dunaliella tertiolecta and Phaeodactylum tricornutum) [17] but also freshwater ones (Chlorella vulgaris, [21] Chlorella sp., [22] Chlamydomonas reinhardtii [23,24] and Monoraphidium arcuatum [22] ) can produce arsenosugars from incorporated As V by reduction and methylation processes, and that cyanobacteria (freshwater species, Microcystis sp. PCC 7806, Nostoc sp.…”