The microbial ars operon encodes the primary bacterial defense response to the environmental toxicant, arsenic. An important component of this operon is the arsR gene, which encodes ArsR, a member of the family of proteins categorized as DNA-binding transcriptional repressors. As currently documented, ArsR regulates its own expression as well as other genes in the same ars operon. This study examined the roles of four ArsR proteins in the well-developed model Gram-negative bacterium Agrobacterium tumefaciens 5A. RNASeq was used to compare and characterize gene expression profiles in ± arsenite-treated cells of the wild-type strain and in four different arsR mutants. We report that ArsR-controlled transcription regulation is truly global, extending well beyond the current ars operon model, and includes both repression as well as apparent activation effects. Many cellular functions are significantly influenced, including arsenic resistance, phosphate acquisition/metabolism, sugar transport, chemotaxis, copper tolerance, iron homeostasis, and many others. While there is evidence of some regulatory overlap, each ArsR exhibits its own regulatory profile. Furthermore, evidence of a regulatory hierarchy was observed; i.e. ArsR1 represses arsR4 , ArsR4 activates arsR2 , and ArsR2 represses arsR3 . Additionally and unexpectedly, aioB (arsenite oxidase small subunit) expression was shown to be under partialmore »
High Arsenic Levels Increase Activity Rather than Diversity or Abundance of Arsenic Metabolism Genes in Paddy Soils
ABSTRACT Arsenic (As) metabolism genes are generally present in soils, but their diversity, relative abundance, and transcriptional activity in response to different As concentrations remain unclear, limiting our understanding of the microbial activities that control the fate of an important environmental pollutant. To address this issue, we applied metagenomics and metatranscriptomics to paddy soils showing a gradient of As concentrations to investigate As resistance genes ( ars ) including arsR , acr3 , arsB , arsC , arsM , arsI , arsP , and arsH as well as energy-generating As respiratory oxidation ( aioA ) and reduction ( arrA ) genes. Somewhat unexpectedly, the relative DNA abundances and diversities of ars , aioA , and arrA genes were not significantly different between low and high (∼10 versus ∼100 mg kg −1 ) As soils. Compared to available metagenomes from other soils, geographic distance rather than As levels drove the different compositions of microbial communities. Arsenic significantly increased ars gene abundance only when its concentration was higher than 410 mg kg −1 . In contrast, metatranscriptomics revealed that relative to low-As soils, high-As soils showed a significant increase in transcription of ars and aioA genes, which are induced by arsenite, the more »
- Editors:
- Cann, Isaac
- Publication Date:
- NSF-PAR ID:
- 10337093
- Journal Name:
- Applied and Environmental Microbiology
- Volume:
- 87
- Issue:
- 20
- ISSN:
- 0099-2240
- Sponsoring Org:
- National Science Foundation
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- https://doi.org/10.1128/AEM.01383-21
