(Levy et al., 2005; Maeda et al., 1

(Levy et al., 2005; Maeda et al., 1992) or to generate energy to
support cellular growth (Mateos et al., 2010; Oremland and Stolz,
2003). Microbial biotransformation of highly toxic As
III
includes
oxidation to As
V
and methylation to MetAs forms.
2.1. Oxidation of arsenite by microorganisms
Oxidation of As
III
to As
V
is an energy-producing reaction since
As
III
can serve as electron donor in this process (Mateos et al., 2010;
Páez-Espino et al., 2009). Over the past decade, many microorganisms, including eubacteria and archaea, have been reported
to be using energy generated from the oxidation or reduction
of As oxyanions (Oremland and Stolz, 2003). Microbial mats
predominantly composed of filamentous microorganisms (algae,
presumably Cyanidium and bacteria, similar to Hydrogenobacter acidophilus) have been reported to be responsible for rapid oxidation
of As
III
in a hot spring ecosystem within the Yellowstone National
Park (Langner et al., 2001). A study by Kulp et al. (2008) presented the evidence for As
III
-supported anoxygenic photosynthesis
in naturally-occurring microbial mats of photosynthetic bacteria from Mono Lake (California). They also provided evidence of
photoautotrophic growth of purple bacteria supported by As
III
oxidation to As
V
. The mechanisms of As
III
oxidation by microorganisms
include chemolithoautotrophic metabolism where As
III
is used as
an energy source (Santini et al., 2000) and extracellular oxidation
of As
III
via an arsenite oxidase (Langner et al., 2001).
2.2. Reduction of arsenate by microorganisms
Biomethylation of iAs has been commonly observed in prokaryotic and eukaryotic photosynthetic microorganisms such
as microalgae and cyanobacteria (Ye et al., 2012). Because of
physicochemical similarities between As
V
and phosphate, these
photosynthetic microorganisms actively take up As
V
through the
PO
3−
4
uptake system and then biotransform As
V
inside their cells
(Fig. 1A) (Hasegawa et al., 2001; Suhendrayatna and Maeda, 2001;
Yin et al., 2011). The toxicity of As
V
is due to binding of AsO
3−
4
at
places where PO
3−
4
is essential inside the cells (Hellweger et al.,
2003). To reduce the toxic effect, the photosynthetic microorganisms biotransform As
V
inside their cells in a process that involves a
two-electron reduction of pentavalent As
V
to trivalent As
III
, mediated by glutathione (Fig. 1B) (Hughes, 2002).
2.3. Biomethylation of iAs by phytoplankton
Inside the cells of photosynthetic organisms, As
V
is reduced to
As
III
followed by oxidative methylation of intermediate trivalent
MetAs species (MMA
III
and DMAIII
) to pentavalent MetAs species
(MMA
V
and DMAV
) (Hughes, 2002). A number of freshwater and
marine phytoplankton have been reported to biomethylate iAs
(Caumette et al., 2011; Hirata and Toshimitsu, 2005; LlorenteMirandes et al., 2010; Miyashita et al., 2011; Slejkovec et al., 2006).
The concentrations of different arsenic species in phytoplankton
and macroalgae is listed in Table 1. A study by Hasegawa et al.
(2001) showed that a freshwater phytoplankton (Closterium aciculare) converts As
V
predominantly (∼80%) into the less toxic
pentavalent methylated intermediate (DMA
V
), with trace concentrations of trivalent MetAs. The biotransformation of As
V
by marine
and freshwater phytoplankton is discussed in detail elsewhere
(Rahman and Hasegawa, 2011).
Arsenate reduction and methylation rates in freshwater environments are often dependent on the dynamics of phytoplankton
blooms, which are affected by nutrient enrichment and seasonal
variables such as light and temperature (Hasegawa et al., 2010;
Hasegawa et al., 2009; Rahman and Hasegawa, 2012). Sohrin et al.
(1997) reported seasonal variations of As speciation in Lake Biwa,
Japan, where the concentrations of As
III
increased in spring and

Results (English) 2:

（Levy等。，2005；田等人。，1992）或以产生能量
支持细胞的生长（马特奥斯等人。，2010；和
Oremland Stolz，2003）。微生物转化的高毒性的
III
包括
氧化为
V
和甲基化转移的形式。
2.1。由微生物
氧化氧化砷作为
III
为
V
是一个能源生产反应自
作为
III
在这个过程中，可以作为电子供体（马特奥斯等人。，2010；
PáEZ埃斯皮诺等人。，2009）。在过去的十年中，许多微生物，包括细菌和古细菌，已被报道
是使用从氧化或还原
产生的含氧阴离子的能量（2003和Oremland Stolz，）。微生物
主要由丝状微生物（藻类，
大概是氰化物和细菌，嗜酸乳杆菌与嗜热氢）已报告给负责快速氧化
作为
III
在温泉生态系统内的黄石国家公园（
兰纳等人。，2001）。库普等人的研究。（2008）提出的证据为
III
载氧光合作用
在自然光合细菌微生物莫诺湖（加利福尼亚）。他们还提供证据的
光自养生长的紫细菌支持为
III
氧化为
V
。的机制，
微生物
III
氧化包括chemolithoautotrophic代谢而
III
作为
能量源（桑蒂尼等人。，2000）和胞外氧化
作为
III
通过砷氧化酶（兰纳等人。，2001）。
2.2。由微生物
biomethylation IAS还原砷酸盐已在原核光合微生物
作为微藻和蓝藻和真核通常观察到的（你们等人。，2012）。因为
理化之间的相似性为
V
和磷，这些
光合微生物积极采取了
V
通过
坡
3−
4
吸收系统，然后转化为
V
细胞内部的
（图1a）（Hasegawa等人。，2001；suhendrayatna和田，2001；
阴等人。，2011）。作为
V
的毒性是由于结合的ASO
3−
4
在
地方坡
3−
4
是必不可少的细胞内（hellweger等人。
，2003）。为了减少毒性作用，光合微生物转化为
V
在他们的细胞中的一种，包括
两电子还原五价砷
V
三价作为
III
过程，介导的谷胱甘肽（图1b）（休斯，2002）。
2.3。浮游植物光合生物的细胞内
IAS生物甲基化，作为
V
减少到
作为
III
其次是中间三价
转移物种氧化甲基化（MMA
III
DMAIII
）为五价金属物种
（MMA
V
和DMAV
）（休斯，2002）。大量的淡水和海洋浮游植物
已报道biomethylate IAS
（caumette等人。，2011；2005；他和Toshimitsu，llorentemirandes等人。，2010；宫等人。，2011；slejkovec等人。，2006）。
浮游植物和藻类
不同砷物种的浓度表1中列出的。利用Hasegawa等人的研究。
（2001）表明，淡水浮游植物（硅藻aciculare）转换为
V
主要（∼80%）为毒性较低的
五价甲基中间体（DMA
V
），与三价金属微量浓度。生物转化为
V
海洋和淡水浮游植物
其他地方详细讨论
（拉赫曼和Hasegawa，2011）。
在淡水环境中砷的还原和甲基化率往往依赖于浮游植物水华动力学
，这是由富营养化和季节性
变量如光照和温度的影响（Hasegawa等人。，2010；
Hasegawa等人。，2009；拉赫曼和Hasegawa，2012）。sohrin等人。
（1997）报道，在琵琶湖的季节性变化的形态，
日本，在浓度为
在春天
增加