Contribution of Arsenic Species in Unicellular Algae to the Cycling of Arsenic in Marine Ecosystems

Abstract

This review investigates the arsenic species produced by and found in marine unicellular algae to determine if unicellular algae contribute to the formation of arsenobetaine (AB) in higher marine organisms. A wide variety of arsenic species have been found in marine unicellular algae including inorganic species (mainly arsenate--As(V)), methylated species (mainly dimethylarsenate (DMA)), arsenoribosides (glycerol, phosphate, and sulfate) and metabolites (dimethylarsenoethanol (DMAE)). Subtle differences in arsenic species distributions exist between chlorophyte and heterokontophyte species with As(V) commonly found in water-soluble cell fractions of chlorophyte species, while DMA is more common in heterokontophyte species. Additionally, different arsenoriboside species are found in each phyla with glycerol and phosphate arsenoribosides produced by chlorophytes, whereas glycerol, phosphate, and sulfate arsenoribosides are produced by heterokontophytes, which is similar to existing data for marine macro-algae. Although arsenoribosides are the major arsenic species in many marine unicellular algal species, AB has not been detected in unicellular algae which supports the hypothesis that AB is formed in marine animals via the ingestion and further metabolism of arsenoribosides. The observation of significant DMAE concentrations in some unicellular algal cultures suggests that unicellular algae-based detritus contains arsenic species that can be further metabolized to form AB in higher marine organisms. Future research establishing how environmental variability influences the production of arsenic species by marine unicellular algae and what effect this has on arsenic cycling within marine food webs is essential to clarify the role of these organisms in marine arsenic cycling.

Review of arsenic speciation, toxicity and metabolism in microalgae

“…Many studies showed that As(V) was the major arsenic species accounting for up to 99 % of the total As in cystolic fractions of microalgae cells (Duncan et al 2015;Goessler et al 1997;Levy et al 2005;Ohki et al 1999;Wang et al 2013b). Moreover, the As(III) oxidation of most microalgae occurs either in the periplasm or near the outer membrane, which should be regarded as a kind of survival mechanism over the long term evolution (Zhang et al 2014).…”

“…Arsenolipids could be degraded to some toxic arsenic species (Meyer et al 2014;Taleshi et al 2014), so further investigation should be conducted on the possible toxic properties of these lipids and their influence on human health. Moreover, further research on the formation of arsenolipid species in microalgae is essential to understand the role of these organoarsenic compounds in As cycling (Duncan et al 2015). …”

“…) cells. Living at the very bottom of the food chain, they are widely distributed in terrestrial and marine environments and play an important role in arsenic cycling (Duncan et al 2015;Lee 2008;Maeda et al 1990Maeda et al , 1993. Arsenic species in microalgae may be separated into different biochemical cell fractions, i.e., water-soluble (cystolic), lipid-soluble (lipid), and residual (cell membranes and debris) fractions (Duncan et al 2010(Duncan et al , 2013a(Duncan et al , b, 2015Foster et al 2008).…”

“…Methylated arsenic species [MMA(V), DMA(V) and trimethylarsine (TMA)] are relatively minor or even below the detection limit (Karadjova et al 2008;Lai et al 1997;Levy et al 2005;Miyashita et al 2011). So far, there is no report about the existence of AB and AC in microalgae (Table 1) (Caumette et al 2012;Duncan et al 2013aDuncan et al , 2015. Some microalgae species, e.g., Chlorella, Spirulina and Dunaliella contain significant amount of valuable proteins, b-carotene, vitamins, and carotenoids etc., thus their nutritional value is highly recognized (Hosseini Tafreshi and Shariati 2009;Khan et al 2005;Merchant et al 2000;Raja et al 2007).…”

“…To our knowledge, so far only one review article was published on the As speciation in microalgal cells and its role in the As cycling in marine environment (Duncan et al 2015). Since microalgae research is important in both phycoremediation of wastewater and pollution prevention of algal products, more in-depth understanding of As metabolism in microalgae is urgently needed.…”