Biotransformation of arsenate to arsenosugars by Chlorella vulgaris

Abstract

Chlorella vulgaris was cultivated in a growth medium containing arsenate concentration of <0.01, 10, 100 and 1000 mg l −1 . Illumination was carried out in 12 h cycles for 5 days. The health status of the culture was monitored by continuous pH and dissolved oxygen (DO) readings. Destructive sampling was used for the determination of biomass, chlorophyll, total arsenic and arsenic species. The chlorophyll a content, the DO and pH cycles were not significantly different for the different arsenate concentrations in the culture. In contrast, biomass production was significantly (p < 0.05) increased for the arsenic(V) treatment at 1000 mg l −1 compared with 100 mg l −1 .The arsenic concentration in the algae increased with the arsenate concentration in the culture. However, the bioconcentration factor decreased a hundred-fold with increase of arsenate from the background level to 1000 mg l −1 . The arsenic species were identified by using strong anion-exchange high-performance liquid chromatography-inductively coupled plasma mass spectrometry analysis after methanol/water (1 : 1) extraction. The majority (87-100%) of the extractable arsenic was still arsenate; arsenite was found to be between 1 and 6% of total extractable arsenic in the algae. In addition to dimethylarsinic acid, one unknown arsenical (almost co-eluting with methylarsonic acid) and three different arsenosugars have been identified for the first time in C. vulgaris growing in a culture containing a mixture of antibiotics and believed to be axenic. The transformation to arsenosugars in the algae is not dependent on the arsenate concentration in the culture and varies between 0.2 and 5% of total accumulated arsenic. Although no microbiological tests for bacterial contamination were made, this study supports the hypothesis that algae, and not associated bacteria, produce the arsenosugars.

Biosynthesis of arsenolipids by the cyanobacterium Synechocystis sp. PCC 6803

“…For example, the bio-concentration factor decreased from 1505 to 62 when arsenic exposure increased from 0.1 to 100 mM (Table 1) for Synechocystis WT. Similar results have also been found for the green alga Chlorella vulgaris, [25,26] the marine cyanobacterium Phormidium sp. [27] and the freshwater fish, Tilapia mossambica.…”

Arsenic biotransformation in earthworms from contaminated soils

“…2, a) which in turn is converted to arsenosugars through addition of the adenosyl group from S-adenosylmethionine (SAM). 29 This nucleoside then undergoes glycosidation to produce a 95 range of arsenosugars. 15,29 These arsenosugars are thought to subsequently be converted to AB along a pathway involving either arsenocholine (AC) or dimethylarsinoylacetate (DMAA) 12 (Fig.…”

Cyanobacteria produce arsenosugars

“…[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.…”