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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

Proposed arsenic metabolic model for R. palustris CGA009.
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Figure 7: Proposed arsenic metabolic model for R. palustris CGA009.

Mentions: A working model for the arsenic detoxification by the arsenic multi-operons was proposed in R. palustris (Figure 7). In this model, the As(V) enters into cells through inorganic phosphate (Pit) or phosphate specific transport (Pst) systems (Kruger et al., 2013); once As(V) arrives inside the cells, it is reduced to As(III) by ArsC produced from ars1 and/or ars2 operon (possible at a low expression) (Figure 3). As(III) formed in the reaction then inactivates ArsR, initiating the transcription of the arsRRCC (acr3) operon (ars2). Due to the two copies of arsC in ars2, it allows to reduce arsenate more promptly, leading to As(III) accumulation in the cells. If the accumulated As(III) could not be expelled out of the cells by arsenite permease (Acr3), the increasing As(III) triggers the ars3 transcription by releasing ArsR which originally binds arsM promoter/operator. Arsenic resistance genetic units ars2 and ars3 in R. palustris contribute to detoxifying arsenic at a high dose because their transcription level is comparable when cells are treated with 1.0 mM arsenite. With cooperation of ars2 and ars3, R. palustris detoxifying As(III) by extruding it out of the cell by As(III) transporter (Acr3) or transforming As(III) to volatile methylated As(III) (TMA) by ArsM. It is reasonable to assume that ars2 is more important when cells are exposed to lower levels of arsenic due to its activity expression. However, a relatively complex arsenate detoxification system described here suggests that R. palustris growing in the natural environment must be equipped to deal with rapidly changing and perhaps relatively high levels of arsenic.


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)

Proposed arsenic metabolic model for R. palustris CGA009.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 7: Proposed arsenic metabolic model for R. palustris CGA009.
Mentions: A working model for the arsenic detoxification by the arsenic multi-operons was proposed in R. palustris (Figure 7). In this model, the As(V) enters into cells through inorganic phosphate (Pit) or phosphate specific transport (Pst) systems (Kruger et al., 2013); once As(V) arrives inside the cells, it is reduced to As(III) by ArsC produced from ars1 and/or ars2 operon (possible at a low expression) (Figure 3). As(III) formed in the reaction then inactivates ArsR, initiating the transcription of the arsRRCC (acr3) operon (ars2). Due to the two copies of arsC in ars2, it allows to reduce arsenate more promptly, leading to As(III) accumulation in the cells. If the accumulated As(III) could not be expelled out of the cells by arsenite permease (Acr3), the increasing As(III) triggers the ars3 transcription by releasing ArsR which originally binds arsM promoter/operator. Arsenic resistance genetic units ars2 and ars3 in R. palustris contribute to detoxifying arsenic at a high dose because their transcription level is comparable when cells are treated with 1.0 mM arsenite. With cooperation of ars2 and ars3, R. palustris detoxifying As(III) by extruding it out of the cell by As(III) transporter (Acr3) or transforming As(III) to volatile methylated As(III) (TMA) by ArsM. It is reasonable to assume that ars2 is more important when cells are exposed to lower levels of arsenic due to its activity expression. However, a relatively complex arsenate detoxification system described here suggests that R. palustris growing in the natural environment must be equipped to deal with rapidly changing and perhaps relatively high levels of arsenic.

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