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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

Effects of As (III) concentrations on the expressions of ars1, ars2 and ars3 operons in R. palustris CGA009. The expressions of arsB(■), arsC2(○), and arsM(▴) represent the expression of ars1, ars2, and ars3 operons, respectively. The expression of genes was calculated by determing the content ratio of functional genes to house-keeping gene (gyrB). Cultures were harvested in the middle-log phase (50 h). Error bars indicate the standard deviation from three independent experiments.
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Figure 4: Effects of As (III) concentrations on the expressions of ars1, ars2 and ars3 operons in R. palustris CGA009. The expressions of arsB(■), arsC2(○), and arsM(▴) represent the expression of ars1, ars2, and ars3 operons, respectively. The expression of genes was calculated by determing the content ratio of functional genes to house-keeping gene (gyrB). Cultures were harvested in the middle-log phase (50 h). Error bars indicate the standard deviation from three independent experiments.

Mentions: In this study, we preliminary investigated their respective gene expression in the three ars operons by using quantitative real-time PCR in order to understand which one was actively involved in arsenic resistance in R. palustris CGA009. It should be noted that studying ars operon regulation by As(V) is difficult because it can be quickly reduced to As(III) by As(V) reductase in vivo. Therefore, we first examined the effect of As(III) (rather than As(V)) on the expression of ars1, ars2 and ars3 operons. To do that, we selected the functional genes arsB, arsC2, and arsM as marker genes for ars1, ars2, and ars3 operons, respectively (Figure 4). Gene expression of arsB, arsC2, and arsM were undetectable when As(III) was absent, indicating the three operons were not expressed without arsenic induction. arsB was not transcribed when As(III) was added to the culture at concentrations ranging from 0 to 1.0 mM. Remarkably, the expression of ars2 operon (arsC2) was readably detected when cells were even exposed to a low level of As(III) (0.01 μM). Compared to the control, its transcript level was increased 9.5, 23.8, and 126.8–fold when 0.01, 0.1, and 1.0 mM of As(III) were added respectively, demonstrating that ars2 expression was up-regulated by As(III). However, arsM was not transcribed when the cells were exposed to 1.0 μM of As(III), indicating that gene product of arsM was not critical for detoxifying As(III) under low environmental As(III) conditions (<1.0 μM). However, its expression level was 3.86-fold higher than the control when 1.0 μM concentration of As(III) was present in the medium (Figure 4). Furthermore, arsM transcript level increased with the increasing environmental As(III) concentration (Figure 4). It should be noted that the expression levels of arsM and arsC2 were almost equal when As(III) concentration reached a 1.0 mM, showing that R. palustris CGA009 probably required expression of ars2 and ars3 operons to detoxify the high concentrations of As(III).


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)

Effects of As (III) concentrations on the expressions of ars1, ars2 and ars3 operons in R. palustris CGA009. The expressions of arsB(■), arsC2(○), and arsM(▴) represent the expression of ars1, ars2, and ars3 operons, respectively. The expression of genes was calculated by determing the content ratio of functional genes to house-keeping gene (gyrB). Cultures were harvested in the middle-log phase (50 h). 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 4: Effects of As (III) concentrations on the expressions of ars1, ars2 and ars3 operons in R. palustris CGA009. The expressions of arsB(■), arsC2(○), and arsM(▴) represent the expression of ars1, ars2, and ars3 operons, respectively. The expression of genes was calculated by determing the content ratio of functional genes to house-keeping gene (gyrB). Cultures were harvested in the middle-log phase (50 h). Error bars indicate the standard deviation from three independent experiments.
Mentions: In this study, we preliminary investigated their respective gene expression in the three ars operons by using quantitative real-time PCR in order to understand which one was actively involved in arsenic resistance in R. palustris CGA009. It should be noted that studying ars operon regulation by As(V) is difficult because it can be quickly reduced to As(III) by As(V) reductase in vivo. Therefore, we first examined the effect of As(III) (rather than As(V)) on the expression of ars1, ars2 and ars3 operons. To do that, we selected the functional genes arsB, arsC2, and arsM as marker genes for ars1, ars2, and ars3 operons, respectively (Figure 4). Gene expression of arsB, arsC2, and arsM were undetectable when As(III) was absent, indicating the three operons were not expressed without arsenic induction. arsB was not transcribed when As(III) was added to the culture at concentrations ranging from 0 to 1.0 mM. Remarkably, the expression of ars2 operon (arsC2) was readably detected when cells were even exposed to a low level of As(III) (0.01 μM). Compared to the control, its transcript level was increased 9.5, 23.8, and 126.8–fold when 0.01, 0.1, and 1.0 mM of As(III) were added respectively, demonstrating that ars2 expression was up-regulated by As(III). However, arsM was not transcribed when the cells were exposed to 1.0 μM of As(III), indicating that gene product of arsM was not critical for detoxifying As(III) under low environmental As(III) conditions (<1.0 μM). However, its expression level was 3.86-fold higher than the control when 1.0 μM concentration of As(III) was present in the medium (Figure 4). Furthermore, arsM transcript level increased with the increasing environmental As(III) concentration (Figure 4). It should be noted that the expression levels of arsM and arsC2 were almost equal when As(III) concentration reached a 1.0 mM, showing that R. palustris CGA009 probably required expression of ars2 and ars3 operons to detoxify the high concentrations of As(III).

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