Abstract
The hgcAB gene pair encodes mercury (Hg) methylation capability in a diverse group of microorganisms, but its evolution and transcriptional regulation remain unknown. Working from the possibility that the evolutionary function of HgcAB may not be Hg methylation, we test a possible link to arsenic resistance. Using model Hg methylator Pseudodesulfovibrio mercurii ND132, we evaluated transcriptional control of hgcAB by a putative ArsR encoded upstream and cotranscribed with hgcAB. This regulator shares homology with ArsR repressors of arsenic resistance and S-adenosylhomocysteine (SAH)responsive regulators of methionine biosynthesis but is distinct from other ArsR/SahR proteins in P. mercurii. Using quantitative PCR (qPCR) and RNA sequencing (RNA-seq) transcriptome analyses, we confirmed this ArsR regulates hgcAB transcription and is responsive to arsenic and SAH. Additionally, RNA-seq indicated a possible link between hgcAB activity and arsenic transformations, with significant upregulation of other ArsR-regulated arsenic resistance operons alongside hgcAB. Interestingly, wild-type ND132 was less sensitive to As(V) (but not As(III)) than an hgcAB knockout strain, supporting the idea that hgcAB may be linked to arsenic resistance. Arsenic significantly impacted rates of Hg methylation by ND132; however, responses varied with culture conditions. Differences in growth and metabolic activity did not account for arsenic impacts on methylation. While arsenic significantly increased hgcAB expression, hgcAB gene and transcript abundance was not a good predictor of Hg methylation rates. Taken together, these results support the idea that Hg and As cycling are linked in P. mercurii ND132. Our results may hold clues to the evolution of hgcAB and the controls on Hg methylation in nature.
| Original language | English |
|---|---|
| Journal | Applied and Environmental Microbiology |
| Volume | 89 |
| Issue number | 4 |
| DOIs | |
| State | Published - Apr 2023 |
Funding
Caitlin M. Gionfriddo was a Robert and Arlene Kogod Secretarial Scholar with the Smithsonian Environmental Research Center while conducting work described in this paper. This work was funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Subsurface Biogeochemical Research (SBR) Program, and is a product of the Critical Interfaces Science Focus Area at Oak Ridge National Laboratory, which is managed by UT-Battelle, LLC, under contract no. DE-AC05-00OR22725 with the U.S. Department of Energy. Caitlin M. Gionfriddo was a Robert and Arlene Kogod Secretarial Scholar with the Smithsonian Environmental Research Center while conducting work described in this paper. This work was funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Subsurface Biogeochemical Research (SBR) Program, and is a product of the Critical Interfaces Science Focus Area at Oak Ridge National Laboratory, which is managed by UT-Battelle, LLC, under contract no. DE-AC05-00OR22725 with the U.S. Department of Energy. The As speciation analysis was performed by Brooks Applied Labs, and we thank Ben Wozniak and Collette Machado for technical support. The RNA-seq transcriptome analyses were performed at Azenta US Inc., and we thank Andrew Corbin and Eric Danzeisen for technical support. We thank the reviewers for taking the time and effort to review the manuscript and for their insightful comments and suggestions.
Keywords
- ArsR
- RNA-seq
- ars operon
- arsenic
- arsenic resistance
- hgcAB
- mercury
- mercury biogeochemistry
- methylmercury