Elucidating pathway arsenic methylation
Arsenite [As(III)] and methylarsenite [MAs(III)] are the most toxic inorganic and methylated arsenicals, respectively. As(III) and MAs(III) can be interconverted in the unicellular cyanobacterium Nostoc sp. doi: 10.1007/s11356-013-1741-7 Pub Med Abstract | Cross Ref Full Text | Google Scholar Yan, Y., Ye, J., Xue, X.
MAs(V) can also be reduced to MAs(III) in some bacteria (Yoshinaga et al., 2011), so other microbes have evolved various processes to detoxify MAs(III) as it is formed.
MAs(III), like As(III), is detoxified by oxidation or eﬄux in some microbes. doi: 10.1002/jobm.200800301 Pub Med Abstract | Cross Ref Full Text | Google Scholar Vioque, A. Analysis of the gene encoding the RNA subunit of ribonuclease P from cyanobacteria.
Because of the unavoidable exposure to arsenic, nearly all of the living organisms have arsenic detoxifying systems (Rosen, 2002; Liu et al., 2013).
As(III) eﬄux and oxidation are considered to be efficient detoxification pathways in Bacteria and Archaea (Páez-Espino et al., 2009).
Thus, to investigate the relationship between As(III) methylation and MAs(III) demethylation, we constructed a simplified model using arsenic-hypersensitive Escherichia coli AW3110 strains (Δars RBC) expressing Nsars M or/and Nsars I.
The effect of co-expression on biotransformations of and resistance to As(III) and MAs(III) was examined.
In cyanobacteria, morphological, physiological and biochemical changes, genomics, and proteomics have been found to be involved in response to arsenic stress (Srivastava et al., 2009; Pandey et al., 2012; Sánchez-Riego et al., 2014). Is arsenic biotransformation a detoxification mechanism for microorganisms?
Furthermore, various cyanobacteria were shown to be able to accumulate and resist arsenic by multiple arsenic biotransformations (Yin et al., 2012; Wang et al., 2013). PCC 6803, which is the best-understood cyanobacterium on arsenic resistance and metabolism (Huertas et al., 2014), an ars operon (ars BHC) mediates the main arsenic resistance mechanism (López-Maury et al., 2003), and another two arsenate reductases (ars I1 and ars I2) (López-Maury et al., 2009) and an arsenite methyltransferase (ars M) (Yin et al., 2011) were also found to be the resistance determinants. doi: 10.1073/pnas.0506836103 Pub Med Abstract | Cross Ref Full Text | Google Scholar Rahman, M.
Compared to Ns Ars I, Ns Ars M conferred higher resistance to As(III) and lower resistance to MAs(III) by methylating both As(III) and MAs(III).
The major species found in solution was dimethylarsenate [DMAs(V)].
PCC 7120 (Nostoc), which has both the ars M gene (Nsars M), which is responsible for arsenic methylation, and the ars I gene (Nsars I), which is responsible for MAs(III) demethylation.