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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

Schematic comparison of arsenic gene clusters from seven R. palustris strains. Genes were shown as different color and arrows indicated the direction of transcription. arsR was arsenite-responsive transcriptional regulator gene. arsC/arsC' was As (V) reductases gene, arsC was As (V) reductases genes, arsC1 and arsC2 were glutathione (GSH)/glutaredoxin (Grx)-coupled reductases genes, arsC3 was thioredoxin (Trx)/thioredoxin reductase (TrxR)-dependent reductases gene; arsB was arsenite efflux pump gene, acr3 was arsenite permease (ACR3) gene, they came from unrelated As(III) transporter families; arsH was NADPH-dependent flavin mononucleotide reductase gene; arsM was As(III)-methyltransferase gene. Other genes found in or adjacent to the ars clusters were shown as empty boxes.
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Figure 3: Schematic comparison of arsenic gene clusters from seven R. palustris strains. Genes were shown as different color and arrows indicated the direction of transcription. arsR was arsenite-responsive transcriptional regulator gene. arsC/arsC' was As (V) reductases gene, arsC was As (V) reductases genes, arsC1 and arsC2 were glutathione (GSH)/glutaredoxin (Grx)-coupled reductases genes, arsC3 was thioredoxin (Trx)/thioredoxin reductase (TrxR)-dependent reductases gene; arsB was arsenite efflux pump gene, acr3 was arsenite permease (ACR3) gene, they came from unrelated As(III) transporter families; arsH was NADPH-dependent flavin mononucleotide reductase gene; arsM was As(III)-methyltransferase gene. Other genes found in or adjacent to the ars clusters were shown as empty boxes.

Mentions: The genome-mining analysis showed that arsRBC operon existed in seven R. palustris strains (CGA009, HaA2, TIE-1, DX-1, BisB5, BisA53, and BisB18) (Figure 3), while additional arsRM operon was only found in strains CGA009, HaA2, TIE-1, DX-1, and BisB5 (Figure 3) (Lv et al., 2012a). The first operon resembles ars operon (named ars1 operon, arsRCBH type), consisting of arsenite-responsive transcriptional regulator gene (arsR1), arsenate reductase gene (arsC1), arsenite efflux pump gene (arsB) and NADPH-dependent flavin mononucleotide reductase gene (arsH). The second operon [named ars2 operon, arsRRCC (acr3) type] contains two arsR genes (arsR2 and arsR3), two As(V) reductases genes (arsC2 and arsC3), one arsenite permease gene (acr3), and two genes encoding the hypothetical proteins. Both ars1 and ars2 operons encode these proteins that perform As(V) reduction and As(III) extrusion mechanisms. The third operon (named ars3 operon, arsRM type) consists of arsenite-responsive transcriptional regulator gene (arsR4) and As(III)-methyltransferase gene (arsM). ars3 operon encode methylation protein that methylate As(III) to a number of methylated intermediates such as onomethylarsenite [MMA(III)] and dimethylarsenite [DMA(III)]. It should be note that arsenic resistance in microorganisms did not show a direct correlation with arsenic operon number(s) (Kruger et al., 2013). For example, at least five arsenic operons were found in Herminiimonas arsenicoxydans while its tolerance to arsenic was much lower than that in Corynebacterium glutamicum which has only two arsenic operons. Despite of their widespread distribution in various bacteria, the arsenic multi-operons were understudied. Due to arsenic multi-operons co-existing in one microorganism, it is difficult to define the arsenic resistance mechanisms. Therefore, it is necessary to further investigate how these arsenic multi-operons were differentially regulated and their contributions to arsenic speciation.


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)

Schematic comparison of arsenic gene clusters from seven R. palustris strains. Genes were shown as different color and arrows indicated the direction of transcription. arsR was arsenite-responsive transcriptional regulator gene. arsC/arsC' was As (V) reductases gene, arsC was As (V) reductases genes, arsC1 and arsC2 were glutathione (GSH)/glutaredoxin (Grx)-coupled reductases genes, arsC3 was thioredoxin (Trx)/thioredoxin reductase (TrxR)-dependent reductases gene; arsB was arsenite efflux pump gene, acr3 was arsenite permease (ACR3) gene, they came from unrelated As(III) transporter families; arsH was NADPH-dependent flavin mononucleotide reductase gene; arsM was As(III)-methyltransferase gene. Other genes found in or adjacent to the ars clusters were shown as empty boxes.
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Related In: Results  -  Collection

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Figure 3: Schematic comparison of arsenic gene clusters from seven R. palustris strains. Genes were shown as different color and arrows indicated the direction of transcription. arsR was arsenite-responsive transcriptional regulator gene. arsC/arsC' was As (V) reductases gene, arsC was As (V) reductases genes, arsC1 and arsC2 were glutathione (GSH)/glutaredoxin (Grx)-coupled reductases genes, arsC3 was thioredoxin (Trx)/thioredoxin reductase (TrxR)-dependent reductases gene; arsB was arsenite efflux pump gene, acr3 was arsenite permease (ACR3) gene, they came from unrelated As(III) transporter families; arsH was NADPH-dependent flavin mononucleotide reductase gene; arsM was As(III)-methyltransferase gene. Other genes found in or adjacent to the ars clusters were shown as empty boxes.
Mentions: The genome-mining analysis showed that arsRBC operon existed in seven R. palustris strains (CGA009, HaA2, TIE-1, DX-1, BisB5, BisA53, and BisB18) (Figure 3), while additional arsRM operon was only found in strains CGA009, HaA2, TIE-1, DX-1, and BisB5 (Figure 3) (Lv et al., 2012a). The first operon resembles ars operon (named ars1 operon, arsRCBH type), consisting of arsenite-responsive transcriptional regulator gene (arsR1), arsenate reductase gene (arsC1), arsenite efflux pump gene (arsB) and NADPH-dependent flavin mononucleotide reductase gene (arsH). The second operon [named ars2 operon, arsRRCC (acr3) type] contains two arsR genes (arsR2 and arsR3), two As(V) reductases genes (arsC2 and arsC3), one arsenite permease gene (acr3), and two genes encoding the hypothetical proteins. Both ars1 and ars2 operons encode these proteins that perform As(V) reduction and As(III) extrusion mechanisms. The third operon (named ars3 operon, arsRM type) consists of arsenite-responsive transcriptional regulator gene (arsR4) and As(III)-methyltransferase gene (arsM). ars3 operon encode methylation protein that methylate As(III) to a number of methylated intermediates such as onomethylarsenite [MMA(III)] and dimethylarsenite [DMA(III)]. It should be note that arsenic resistance in microorganisms did not show a direct correlation with arsenic operon number(s) (Kruger et al., 2013). For example, at least five arsenic operons were found in Herminiimonas arsenicoxydans while its tolerance to arsenic was much lower than that in Corynebacterium glutamicum which has only two arsenic operons. Despite of their widespread distribution in various bacteria, the arsenic multi-operons were understudied. Due to arsenic multi-operons co-existing in one microorganism, it is difficult to define the arsenic resistance mechanisms. Therefore, it is necessary to further investigate how these arsenic multi-operons were differentially regulated and their contributions to arsenic speciation.

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