Cyanobacteria-Mediated Arsenic Redox Dynamics Is Regulated by Phosphate in Aquatic Environments

Studies of cyanobacteria in environments where arsenic (As) and phosphate (P) both occur in significant concentrations have so far only focused on the effect of P on As­(V) toxicity and bioaccumulation, with little attention to the influence of P on As redox transformations. Our study revealed that As­(III) oxidation by <i>Synechocystis</i> appeared to be more effective with increased P levels. We demonstrated that the higher As­(III) percentage in the medium under P-limited conditions was due to enhanced As­(V) uptake and the subsequent efflux of intracellularly reduced As­(III) which in turn contributed to higher As­(III) concentrations in the medium. Arsenic redox changes by <i>Synechocystis</i> under P-limited conditions is a dynamic cyclic process that includes the following: surface As­(III) oxidation (either in the periplasm or near the outer membrane), As­(V) uptake, intracellular As­(V) reduction, and As­(III) efflux. These observations not only expand our understanding of how P influences microbial As redox metabolisms but also provide insights into the biogeochemical coupling between As and P in As contaminated eutrophic aquatic environments and artificial wetland-paddy fields

Additional file 1: of Two draft genome sequences of Pseudomonas jessenii strains isolated from a copper contaminated site in Denmark

Table S1. Phenotypic characteristics of C2, H16 and phylogenetically related P. jessenii CIP 105275T. (DOCX 59 kb

Comparison of Metals and Tetracycline as Selective Agents for Development of Tetracycline Resistant Bacterial Communities in Agricultural Soil

Environmental selection of antibiotic resistance may be caused by either antibiotic residues or coselecting agents. Using a strictly controlled experimental design, we compared the ability of metals (Cu or Zn) and tetracycline to (co)­select for tetracycline resistance in bacterial communities. Soil microcosms were established by amending agricultural soil with known levels of Cu, Zn, or tetracycline known to represent commonly used metals and antibiotics for pig farming. Soil bacterial growth dynamics and bacterial community-level tetracycline resistance were determined using the [³H]­leucine incorporation technique, whereas soil Cu, Zn, and tetracycline exposure were quantified by a panel of whole-cell bacterial bioreporters. Tetracycline resistance increased significantly in soils containing environmentally relevant levels of Cu (≥365 mg kg^–1) and Zn (≥264 mg kg^–1) but not in soil spiked with unrealistically high levels of tetracycline (up to 100 mg kg^–1). These observations were consistent with bioreporter data showing that metals remained bioavailable, whereas tetracycline was only transiently bioavailable. Community-level tetracycline resistance was correlated to the initial toxicant-induced inhibition of bacterial growth. In conclusion, our study demonstrates that toxic metals in some cases may exert a stronger selection pressure for environmental selection of resistance to an antibiotic than the specific antibiotic itself

Copper Tolerance Mechanisms of <i>Mesorhizobium amorphae</i> and Its Role in Aiding Phytostabilization by <i>Robinia pseudoacacia</i> in Copper Contaminated Soil

The legume–rhizobium symbiosis has been proposed as an important system for phytoremediation of heavy metal contaminated soils due to its beneficial activity of symbiotic nitrogen fixation. However, little is known about metal resistant mechanism of rhizobia and the role of metal resistance determinants in phytoremediation. In this study, copper resistance mechanisms were investigated for a multiple metal resistant plant growth promoting rhizobium, Mesorhizobium amorphae 186. Three categories of determinants involved in copper resistance were identified through transposon mutagenesis, including genes encoding a P-type ATPase (CopA), hypothetical proteins, and other proteins (a GTP-binding protein and a ribosomal protein). Among these determinants, <i>copA</i> played the dominant role in copper homeostasis of M. amorphae 186. Mutagenesis of a hypothetical gene <i>lipA</i> in mutant M_lipA exhibited pleiotropic phenotypes including sensitivity to copper, blocked symbiotic capacity and inhibited growth. In addition, the expression of <i>cusB</i> encoding part of an RND-type efflux system was induced by copper. To explore the possible role of copper resistance mechanism in phytoremediation of copper contaminated soil, the symbiotic nodulation and nitrogen fixation abilities were compared using a wild-type strain, a <i>copA</i>-defective mutant, and a <i>lipA</i>-defective mutant. Results showed that a <i>copA</i> deletion did not affect the symbiotic capacity of rhizobia under uncontaminated condition, but the protective role of <i>copA</i> in symbiotic processes at high copper concentration is likely concentration-dependent. In contrast, inoculation of a <i>lipA</i>-defective strain led to significant decreases in the functional nodule numbers, total N content, plant biomass and leghemoglobin expression level of Robinia pseudoacacia even under conditions of uncontaminated soil. Moreover, plants inoculated with <i>lipA</i>-defective strain accumulated much less copper than both the wild-type strain and the <i>copA</i>-defective strain, suggesting an important role of a healthy symbiotic relationship between legume and rhizobia in phytostabilization

Raw dataset

There are seven excel files in this dataset. The spreadsheets "OTU table (bacteria; Anhui)”, “OTU table (fungi; Jiangxi)”, “OTU table(bacteria; Jiangxi)”,“OTU table(fungi; Anhui)”,“Enzyme activity”,“Phylogenetic diversity”and “Physicochemical properties” contain the raw data used in this paper, where a description of all the variables and units can be found

Proteomics and Genetics for Identification of a Bacterial Antimonite Oxidase in <i>Agrobacterium tumefaciens</i>

Antimony (Sb) and its compounds are listed by the United States Environmental Protection Agency (USEPA, 1979) and the European Union (CEC, 1976) as a priority pollutant. Microbial redox transformations are presumed to be an important part of antimony cycling in nature; however, regulation of these processes and the enzymology involved are unknown. In this study, comparative proteomics and reverse transcriptase-PCR analysis of Sb­(III)-oxidizing bacterium <i>Agrobacterium tumefaciens</i> GW4 revealed an oxidoreductase (<i>anoA</i>) is widely distributed in microorganisms, including at least some documented to be able to oxidize Sb­(III). Deletion of the <i>anoA</i> gene reduced Sb­(III) resistance and decreased Sb­(III) oxidation by ∼27%, whereas the <i>anoA</i> complemented strain was similar to the wild type GW4 and a GW4 <i>anoA</i> overexpressing strain increased Sb­(III) oxidation by ∼34%. Addition of Sb­(III) up-regulated <i>anoA</i> expression and cloning <i>anoA</i> to <i>Escherichia coli</i> demonstrated direct transferability of this activity. A His-tag purified AnoA was found to require NADP⁺ as cofactor, and exhibited a <i>K</i>_m for Sb­(III) of 64 ± 10 μM and a <i>V</i>_max of 150 ± 7 nmol min^–1 mg^–1. This study contributes important initial steps toward a mechanistic understanding of microbe-antimony interactions and enhances our understanding of how microorganisms participate in antimony biogeochemical cycling in nature

Arsenic Methyltransferase is Involved in Arsenosugar Biosynthesis by Providing DMA

Arsenic is an ubiquitous toxic element in the environment, and organisms have evolved different arsenic detoxification strategies. Studies on arsenic biotransformation mechanisms have mainly focused on arsenate (As­(V)) reduction, arsenite (As­(III)) oxidation, and arsenic methylation; little is known, however, about the pathway for the biosynthesis of arsenosugars, which are significant arsenic transformation products. Here, the involvement of As­(III) <i>S</i>-Adenosylmethionine methyltransferase (ArsM) in arsenosugar synthesis is demonstrated for the first time. <i>Synechocystis</i> sp. PCC 6803 incubated with As­(III) or monomethylarsonic acid (MMA­(V)) produced dimethylarsinic acid (DMA­(V)) and arsenosugars, as determined by high performance liquid chromatography–inductively coupled plasma mass spectrometry (HPLC/ICPMS). Arsenosugars were also detected in the cells when they were exposed to DMA­(V). A mutant strain <i>Synechocystis</i> Δ<i>arsM</i> was constructed by disrupting <i>arsM</i> in <i>Synechocystis</i> sp. PCC 6803. Methylation of arsenic species was not observed in the mutant strain after exposure to arsenite or MMA­(V); when <i>Synechocystis</i> Δ<i>arsM</i> was incubated with DMA­(V), arsenosugars were detected in the cells. These results suggest that ArsM is a required enzyme for the methylation of inorganic arsenicals, but not required for the synthesis of arsenosugars from DMA, and that DMA is the precursor of arsenosugar biosynthesis. The findings will stimulate more studies on the biosynthesis of complex organoarsenicals, and lead to a better understanding of the bioavailability and function of the organoarsenicals in biological systems