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Insights into arsenic multi-operons expression and resistance mechanisms in Rhodopseudomonas palustris CGA009.

Zhao C, Zhang Y, Chan Z, Chen S, Yang S - Front Microbiol (2015)

Bottom Line: Furthermore, ars2 and ars3 operons were maximally transcribed in the early log-phase where ars2 operon was 5.4-fold higher than that of ars3 operon.A low level of ars1 transcript was only detected at 43 h (early log-phase).Arsenic speciation analysis demonstrated that R. palustris could reduce As(V) to As(III).

View Article: PubMed Central - PubMed

Affiliation: Department of Bioengineering and Biotechnology, Huaqiao University Xiamen, China.

ABSTRACT
Arsenic (As) is widespread in the environment and causes numerous health problems. Rhodopseudomonas palustris has been regarded as a good model organism for studying arsenic detoxification since it was first demonstrated to methylate environmental arsenic by conversion to soluble or gaseous methylated species. However, the detailed arsenic resistance mechanisms remain unknown though there are at least three arsenic-resistance operons (ars1, ars2, and ars3) in R. palustris. In this study, we investigated how arsenic multi-operons contributed to arsenic detoxification in R. palustris. The expression of ars2 or ars3 operons increased with increasing environmental arsenite (As(III)) concentrations (up to 1.0 mM) while transcript of ars1 operon was not detected in the middle log-phase (55 h). ars2 operon was actively expressed even at the low concentration of As(III) (0.01 μM), whereas the ars3 operon was expressed at 1.0 μM of As(III), indicating that there was a differential regulation mechanism for the three arsenic operons. Furthermore, ars2 and ars3 operons were maximally transcribed in the early log-phase where ars2 operon was 5.4-fold higher than that of ars3 operon. A low level of ars1 transcript was only detected at 43 h (early log-phase). Arsenic speciation analysis demonstrated that R. palustris could reduce As(V) to As(III). Collectively, strain CGA009 detoxified arsenic by using arsenic reduction and methylating arsenic mechanism, while the latter might occur with the presence of higher concentrations of arsenic.

No MeSH data available.


Related in: MedlinePlus

Arsenic speciation of R. palustris CGA009 determined by anion exchange HPLC-ICP-MS. (A) Chromatogram of the standards, including As (III), dimethylarsine (DMA), monomethylarsine (MMA) and As (V). (B) Speciation of arsenic of R. palustris CGA009 grown on 1.0 mM arsenite in the middle-log phase. (C) Speciation of arsenic of R. palustris CGA009 grown on 0.5 mM arsenate in the middle-log phase.
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Figure 6: Arsenic speciation of R. palustris CGA009 determined by anion exchange HPLC-ICP-MS. (A) Chromatogram of the standards, including As (III), dimethylarsine (DMA), monomethylarsine (MMA) and As (V). (B) Speciation of arsenic of R. palustris CGA009 grown on 1.0 mM arsenite in the middle-log phase. (C) Speciation of arsenic of R. palustris CGA009 grown on 0.5 mM arsenate in the middle-log phase.

Mentions: HPLC-ICP-MS analysis in middle log-phase demonstrated that As(V) was reduced to As(III), indicating that strain CGA009 detoxified arsenate by reducing As(V) to As(III) by ArsC (Figure 6). However, we failed to detect dimethylarsine (DMA), monomethylarsine (MMA) even in the growth stage where arsM transcript approached to the highest level (Figure 6). DMA and MMA, the intermediates produced in As(III) methylation process did not accumulate in the cells and were immediately converted into volatile trimethylarsine (TMA). Thereafter, TMA were rapidly expelled to extracellular space (Qin et al., 2006). In the same study, Qin et al. heterologously expressed the arsM gene from R. palustris CGA009 in an arsenic-sensitive strain of E. coli. Their results showed that ArsM catalyzed the formation of a number of methylated intermediates from As(III), with TMA as the end product and increased the arsenic resistance, indicating that it was very possible for arsM to be functional in vivo (Qin et al., 2006).


Insights into arsenic multi-operons expression and resistance mechanisms in Rhodopseudomonas palustris CGA009.

Zhao C, Zhang Y, Chan Z, Chen S, Yang S - Front Microbiol (2015)

Arsenic speciation of R. palustris CGA009 determined by anion exchange HPLC-ICP-MS. (A) Chromatogram of the standards, including As (III), dimethylarsine (DMA), monomethylarsine (MMA) and As (V). (B) Speciation of arsenic of R. palustris CGA009 grown on 1.0 mM arsenite in the middle-log phase. (C) Speciation of arsenic of R. palustris CGA009 grown on 0.5 mM arsenate in the middle-log phase.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4585019&req=5

Figure 6: Arsenic speciation of R. palustris CGA009 determined by anion exchange HPLC-ICP-MS. (A) Chromatogram of the standards, including As (III), dimethylarsine (DMA), monomethylarsine (MMA) and As (V). (B) Speciation of arsenic of R. palustris CGA009 grown on 1.0 mM arsenite in the middle-log phase. (C) Speciation of arsenic of R. palustris CGA009 grown on 0.5 mM arsenate in the middle-log phase.
Mentions: HPLC-ICP-MS analysis in middle log-phase demonstrated that As(V) was reduced to As(III), indicating that strain CGA009 detoxified arsenate by reducing As(V) to As(III) by ArsC (Figure 6). However, we failed to detect dimethylarsine (DMA), monomethylarsine (MMA) even in the growth stage where arsM transcript approached to the highest level (Figure 6). DMA and MMA, the intermediates produced in As(III) methylation process did not accumulate in the cells and were immediately converted into volatile trimethylarsine (TMA). Thereafter, TMA were rapidly expelled to extracellular space (Qin et al., 2006). In the same study, Qin et al. heterologously expressed the arsM gene from R. palustris CGA009 in an arsenic-sensitive strain of E. coli. Their results showed that ArsM catalyzed the formation of a number of methylated intermediates from As(III), with TMA as the end product and increased the arsenic resistance, indicating that it was very possible for arsM to be functional in vivo (Qin et al., 2006).

Bottom Line: Furthermore, ars2 and ars3 operons were maximally transcribed in the early log-phase where ars2 operon was 5.4-fold higher than that of ars3 operon.A low level of ars1 transcript was only detected at 43 h (early log-phase).Arsenic speciation analysis demonstrated that R. palustris could reduce As(V) to As(III).

View Article: PubMed Central - PubMed

Affiliation: Department of Bioengineering and Biotechnology, Huaqiao University Xiamen, China.

ABSTRACT
Arsenic (As) is widespread in the environment and causes numerous health problems. Rhodopseudomonas palustris has been regarded as a good model organism for studying arsenic detoxification since it was first demonstrated to methylate environmental arsenic by conversion to soluble or gaseous methylated species. However, the detailed arsenic resistance mechanisms remain unknown though there are at least three arsenic-resistance operons (ars1, ars2, and ars3) in R. palustris. In this study, we investigated how arsenic multi-operons contributed to arsenic detoxification in R. palustris. The expression of ars2 or ars3 operons increased with increasing environmental arsenite (As(III)) concentrations (up to 1.0 mM) while transcript of ars1 operon was not detected in the middle log-phase (55 h). ars2 operon was actively expressed even at the low concentration of As(III) (0.01 μM), whereas the ars3 operon was expressed at 1.0 μM of As(III), indicating that there was a differential regulation mechanism for the three arsenic operons. Furthermore, ars2 and ars3 operons were maximally transcribed in the early log-phase where ars2 operon was 5.4-fold higher than that of ars3 operon. A low level of ars1 transcript was only detected at 43 h (early log-phase). Arsenic speciation analysis demonstrated that R. palustris could reduce As(V) to As(III). Collectively, strain CGA009 detoxified arsenic by using arsenic reduction and methylating arsenic mechanism, while the latter might occur with the presence of higher concentrations of arsenic.

No MeSH data available.


Related in: MedlinePlus