A Novel Arsenate-Resistant Determinant Associated with ICEpMERPH, a Member of the SXT/R391 Group of Mobile Genetic Elements

ICEpMERPH, the first integrative conjugative element (ICE) of the SXT/R391 family isolated in the United Kingdom and Europe, was analyzed to determine the nature of its adaptive functions, its genetic structure, and its homology to related elements normally found in pathogenic Vibrio or Proteus species. Whole genome sequencing of Escherichia coli (E. coli) isolate K802 (which contains the ICEpMERPH) was carried out using Illumina sequencing technology. ICEpMERPH has a size of 110 Kb and 112 putative open reading frames (ORFs). The “hotspot regions” of the element were found to contain putative restriction digestion systems, insertion sequences, and heavy metal resistance genes that encoded resistance to mercury, as previously reported, but also surprisingly to arsenate. A novel arsenate resistance system was identified in hotspot 4 of the element, unrelated to other SXT/R391 elements. This arsenate resistance system was potentially linked to two genes: orf69, encoding an organoarsenical efflux major facilitator superfamily (MFS) transporter-like protein related to ArsJ, and orf70, encoding nicotinamide adenine dinucleotide (NAD)-dependent glyceraldehyde-3-phosphate dehydrogenase. Phenotypic analysis using isogenic strains of Escherichia coli strain AB1157 with and without the ICEpMERPH revealed resistance to low levels of arsenate in the range of 1–5 mM. This novel, low-level resistance may have an important adaptive function in polluted environments, which often contain low levels of arsenate contamination. A bioinformatic analysis on the novel determinant and the phylogeny of ICEpMERPH was presented.

A Parasitic Arsenic Cycle That Shuttles Energy from Phytoplankton to Heterotrophic Bacterioplankton

ABSTRACTIn many regions of the world oceans, phytoplankton face the problem of discriminating between phosphate, an essential nutrient, and arsenate, a toxic analogue. Many phytoplankton, including the most abundant phytoplankton group known,Prochlorococcus, detoxify arsenate (AsV) by reduction to arsenite (AsIII), followed by methylation and excretion of the methylated arsenic products. We synthesized [14C]dimethyl arsenate (DMA) and used it to show that culturedPelagibacterstrain HTCC7211 (SAR11) cells oxidize the methyl group carbons of DMA, producing14CO2and ATP. We measured [14C]DMA oxidation rates in the P-depleted surface waters of the Sargasso Sea, a subtropical ocean gyre. [14C]DMA was oxidized to14CO2by Sargasso Sea plankton communities at a rate that would cause turnover of the estimated DMA standing stock every 8.1 days. SAR11 strain HTCC7211, which was isolated from the Sargasso Sea, has a pair of arsenate resistance genes and was resistant to arsenate, showing no growth inhibition at As/P ratios of >65:1. Across the global oceans, there was a strong inverse relationship between the frequency of the arsenate reductase (LMWPc_ArsC) inPelagibactergenomes and phosphate concentrations. We propose that the demethylation of methylated arsenic compounds byPelagibacterand possibly other bacterioplankton, coupled with arsenate resistance, results in the transfer of energy from phytoplankton to bacteria. We dub this a parasitic cycle because the release of arsenate byPelagibacterin principle creates a positive-feedback loop that forces phytoplankton to continually regenerate arsenate detoxification products, producing a flow of energy to P-limited ocean regions.IMPORTANCEIn vast, warm regions of the oceans, phytoplankton face the problem of arsenic poisoning. Arsenate is toxic because it is chemically similar to phosphate, a scarce nutrient that phytoplankton cells need for growth. Many phytoplankton, including the commonest phytoplankton type in warm oceans,Prochlorococcus, detoxify arsenate by adding methyl groups. Here we show that the most abundant non-photosynthetic plankton in the oceans, SAR11 bacteria, remove the methyl groups, releasing poisonous forms of arsenic back into the water. We postulate that the methylation and demethylation of arsenic compounds creates a cycle in which the phytoplankton can never get ahead and must continually transfer energy to the SAR11 bacteria. We dub this a parasitic process and suggest that it might help explain why SAR11 bacteria are so successful, surpassing all other plankton in their numbers. Field experiments were done in the Sargasso Sea, a subtropical ocean gyre that is sometimes called an ocean desert because, throughout much of the year, there is not enough phosphorous in the water to support large blooms of phytoplankton. Ocean deserts are expanding as the oceans absorb heat and grow warmer.

The Effect of UV Light on Increasing the Arsenate Resistance of Acidithiobacillus Ferrooxidans

Introduction: Mutations are the most popular way to increase the efficiency of mineral waste bioleaching. Acidithiobacillus ferrooxidans are used as an important microorganism in biohydrometallurgy. Arsenate is one of the toxic elements in mines, which reduces the efficiency of A. ferrooxidans leaching. The purpose of this research was to increase the resistance of A. ferrooxidans to high concentrations of arsenate. Materials and Methods: This research was an analytical – descriptive study. The studied population was isolated A. ferrooxidans bacterium from the Sarcheshmeh copper mine in Kerman. The highest tolerable concentration of arsenate was determined by successive cultures of this bacterium at increasing concentrations of arsenate. The bacteria were exposed to UV radiation at different times and then cultured in higher concentrations of arsenate. Results: The results showed that the wild strain was able to grow in the medium containing 20 mM of arsenate. With adaptation, this bacterial strain could grow in medium containing increasing concentrations (40, 60, 80, 100, 120, and 140 mM) of arsenate. When the bacterium was exposed to UV ray for 60 minutes, it was able to grow at a concentration of 120 mM of arsenate. Conclusion: The results indicated a very good effect of UV ray on increasing the arsenate resistance of A. ferrooxidans. It is suggested that this modified strain can be used in real environments for bioleaching.

Glutathione-S-transferase from the arsenic hyperaccumulator fernPteris vittatacan confer increased arsenate resistance inEscherichia coli

Although arsenic is generally a toxic compound, there are a number of ferns in the genusPteristhat can tolerate large concentrations of this metalloid. In order to probe the mechanisms of arsenic hyperaccumulation, we expressed aPteris vittatacDNA library in anEscherichia coli ΔarsC(arsenate reductase) mutant. We obtained three independent clones that conferred increased arsenate resistance on this host. DNA sequence analysis indicated that these clones specify proteins that have a high sequence similarity to the phi class of glutathione-S-transferases (GSTs) of higher plants. Detoxification of arsenate by theP. vittataGSTs inE. coliwas abrogated by agshAmutation, which blocks the synthesis of glutathione, and by agormutation, which inactivates glutathione reductase. Direct measurements of the speciation of arsenic in culture media of theE. colistrains expressing theP. vittataGSTs indicated that these proteins facilitate the reduction of arsenate. Our observations suggest that the detoxification of arsenate by theP. vittataGSTs involves reduction of As(V) to As(III) by glutathione or a related sulfhydro compound.FundingThe authors acknowledge support from the Indiana 21st Century Research and technology Fund (912010479) to DES and LNC, from the U.S. Department of Energy (grant no. DE-FG02-03ER63622) to DES, and from BBSRC-DFID (grant no. BBF0041841GJN) to AAM. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. There are no financial, personal, or professional interests that could be construed to have influenced the paper.

Draft Genome Sequence of Pannonibacter indicus Strain HT23T (DSM 23407T), a Highly Arsenate-Tolerant Bacterium Isolated from a Hot Spring in India

ABSTRACT Pannonibacter indicus strain HT23T, a highly arsenate-tolerant bacterium, was isolated from a tropical hot spring. The estimated genome is 4.2 Mb with 3,818 protein-coding sequences containing putative genes, some of which are involved in arsenate resistance.

Complete Genome Sequences of Evolved Arsenate-Resistant Metallosphaera sedula Strains

Metallosphaera sedula is a thermoacidophilic crenarchaeote with a 2.19-Mb genome. Here, we report the genome sequences of several evolved derivatives of M. sedula generated through adaptive laboratory evolution for enhanced arsenate resistance.