Freshwater phytoplankton: biotransformation of inorganic arsenic to methylarsenic and organoarsenic

Abstract

The biotransformation and detoxification mechanisms of arsenic (As) species have been active research topics because of their significance to environmental and human health. Biotransformation of As in phytoplankton has been extensively studied. However, how different growth phases of phytoplankton impact As biotransformation in them remains uncertain. This study investigated the biotransformation of As species in freshwater phytoplankton at different growth phases to ascertain at which growth phase different types of biotransformation occur. At the logarithmic growth phase, arsenate (As V ) (>90%) and arsenite (As III ) (>80%) predominated in culture media when phytoplankton were exposed to 20 nmol L −1 and 1.0 µmol L −1 of As V , respectively, and methylarsenic (methylAs) species were not detected in them at all. Intracellular As was mainly present in inorganic forms (iAs) at the logarithmic phase, while substantial amounts of organoarsenic (orgAs) species were detected at the stationary phase. At the stationary phase, As V comprised the majority of the total As in culture media, followed by As III and methylAs, although the methylation of As V occurred slowly at the stationary phase. Biotransformation of As V into As III and As methylation inside phytoplankton cells occurred mainly at the logarithmic phase, while the biotransformation of As into complex orgAs compounds occurred at the stationary phase. Phytoplankton rapidly released iAs and methylAs species out of their cells at the logarithmic phase, while orgAs mostly remained inside their cells.

Microalgal Phycoremediation: A Glimpse into a Sustainable Environment

“…The reduction of chromium from the hexavalent oxidation state to the trivalent form is catalysed by the transfer of electrons from the reduced form of GSH [98]. In addition, various detoxifying pathways reduce the toxicity of inorganic arsenic [101]. Some microalgae species appear to be capable of converting arsenic(V) to arsenic (III).…”

Arsenic in Lake Geneva (Switzerland, France): long term monitoring, and redox and methylation speciation in an As unpolluted, oligo-mesotrophic lake

“…52 At the current level of knowledge, it is not possible to relate the observed As retention inside algae to specific phytoplankton species in the lake. Patterns of As biotransformation differ across phytoplankton species 53 with some algal species transforming iAs( v ) efficiently into iAs( iii ) with rapid excretion into the culture medium, while others accumulate iAs( v ) inside their cells or biotransform it into methylated and other organic As species. Those in the lake might belong to both categories.…”

Comunidades microbianas e genes funcionais associados com a ciclagem de arsênio em lagoas salino-alcalinas

“…Este fato pode ser decorrente da capacidade dos micro-organismos em tolerar e/ou metabolizar o As. Devido à semelhança físico-química entre As V (AsO4 3-) e o fosfato (PO4 3-), o fitoplâncton sob condições de depleção de fosfato absorve maiores quantidades de As V através dos transportadores de PO4 3- (Hasegawa et al, 2019;Rahman et al, 2012). Para reduzir o efeito tóxico, os micro-organismos fotossintéticos biotransformam AsV dentro de suas células em um processo que envolve uma redução de dois elétrons de AsV em AsIII, mediado pela glutationa, e posteriormente o AsIII pode sofrer metilação ou ser excretado para fora da células (Ye et al, 2012;Yin et al, 2011).…”