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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

Growth curves of R. palustris CGA009 in the presence of different concentrations of arsenate (A) and arsenite (B), respectively. Strain CGA009 was anaerobically grown at 30°C with continuous illumination. Error bars indicate the standard deviation from three independent experiments.
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Figure 1: Growth curves of R. palustris CGA009 in the presence of different concentrations of arsenate (A) and arsenite (B), respectively. Strain CGA009 was anaerobically grown at 30°C with continuous illumination. Error bars indicate the standard deviation from three independent experiments.

Mentions: Effects of As(V) (0.5~6.0 mM) and As(III) (0.5~2.5 mM) on the bacterial growth of R. palustris were tested in modified Ormerod medium and under anaerobic–light conditions (Figure 1). Negligible difference was observed between the culture supplemented with 0.5 mM of As(V) and the control (no AS(V)), indicating that a low concentration of As(V) was not toxic to R. palustris. The cells could retain at least 60, 70, and 80% of the control growth when 3.0 mM, 2.0 mM and 1.0 mM of As(V) were added to the culture respectively, indicating a good resistance to As(V). However, higher concentrations of As(V) (i.e., 4.0 mM to 6.0 mM) severely inhibited the bacterial growth with the most significant inhibition (nearly 100%) at the concentration of 6.0 mM. R. palustris was more sensitive to environmental As(III) than that in As(V) as shown in Figure 1B. For example, 2.0 mM and 2.5 mM of As(III) inhibited up to 90 and 100% of the bacterial growth, respectively. However, cells retained at least 70 and 60% of the control growth when 1.0 and 1.5 mM of the As(III) were added, respectively. Furthermore, we studied the relationship between the growth rate and the arsenic concentrations (Figure 2). Median effective concentration (EC50) values for As(V) and As(III) were estimated to be 2.44 and 1.55 mM, respectively.


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)

Growth curves of R. palustris CGA009 in the presence of different concentrations of arsenate (A) and arsenite (B), respectively. Strain CGA009 was anaerobically grown at 30°C with continuous illumination. Error bars indicate the standard deviation from three independent experiments.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 1: Growth curves of R. palustris CGA009 in the presence of different concentrations of arsenate (A) and arsenite (B), respectively. Strain CGA009 was anaerobically grown at 30°C with continuous illumination. Error bars indicate the standard deviation from three independent experiments.
Mentions: Effects of As(V) (0.5~6.0 mM) and As(III) (0.5~2.5 mM) on the bacterial growth of R. palustris were tested in modified Ormerod medium and under anaerobic–light conditions (Figure 1). Negligible difference was observed between the culture supplemented with 0.5 mM of As(V) and the control (no AS(V)), indicating that a low concentration of As(V) was not toxic to R. palustris. The cells could retain at least 60, 70, and 80% of the control growth when 3.0 mM, 2.0 mM and 1.0 mM of As(V) were added to the culture respectively, indicating a good resistance to As(V). However, higher concentrations of As(V) (i.e., 4.0 mM to 6.0 mM) severely inhibited the bacterial growth with the most significant inhibition (nearly 100%) at the concentration of 6.0 mM. R. palustris was more sensitive to environmental As(III) than that in As(V) as shown in Figure 1B. For example, 2.0 mM and 2.5 mM of As(III) inhibited up to 90 and 100% of the bacterial growth, respectively. However, cells retained at least 70 and 60% of the control growth when 1.0 and 1.5 mM of the As(III) were added, respectively. Furthermore, we studied the relationship between the growth rate and the arsenic concentrations (Figure 2). Median effective concentration (EC50) values for As(V) and As(III) were estimated to be 2.44 and 1.55 mM, respectively.

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