Functional profiling of mercuric reductase (mer A) genes in biofilm communities of a technical scale biocatalyzer

Heterotrophic Sulfur Oxidation of Halomonas titanicae SOB56 and Its Habitat Adaptation to the Hydrothermal Environment

Halomonas bacteria are ubiquitous in global marine environments, however, their sulfur-oxidizing abilities and survival adaptations in hydrothermal environments are not well understood. In this study, we characterized the sulfur oxidation ability and metabolic mechanisms of Halomonas titanicae SOB56, which was isolated from the sediment of the Tangyin hydrothermal field in the Southern Okinawa Trough. Physiological characterizations showed that it is a heterotrophic sulfur-oxidizing bacterium that can oxidize thiosulfate to tetrathionate, with the Na₂S₂O₃ degradation reaching 94.86%. Two potential thiosulfate dehydrogenase-related genes, tsdA and tsdB, were identified as encoding key catalytic enzymes, and their expression levels in strain SOB56 were significantly upregulated. Nine of fifteen examined Halomonas genomes possess TsdA- and TsdB-homologous proteins, whose amino acid sequences have two typical Cys-X2-Cys-His heme-binding regions. Moreover, the thiosulfate oxidation process in H. titanicae SOB56 might be regulated by quorum sensing, and autoinducer-2 synthesis protein LuxS was identified in its genome. Regarding the mechanisms underlying adaptation to hydrothermal environment, strain SOB56 was capable of forming biofilms and producing EPS. In addition, genes related to complete flagellum assembly system, various signal transduction histidine kinases, heavy metal transporters, anaerobic respiration, and variable osmotic stress regulation were also identified. Our results shed light on the potential functions of heterotrophic Halomonas bacteria in hydrothermal sulfur cycle and revealed possible adaptations for living at deep-sea hydrothermal fields by H. titanicae SOB56.

Analysis of biosorption and biotransformation mechanism of Pseudomonas chengduensis strain MBR under Cd(II) stress from genomic perspective

Microbial treatment of heavy metal-polluted sites is considered an environmentally friendly bioremediation technology with high potential. This study shows that Pseudomonas chengduensis strain MBR, a bacterium that can potentially be applied in the treatment of heavy metal pollution, is most affected by Cd(II) stress at the beginning of its growth. Up to 100% of total Cd(II) adsorption occurs in the first 48 h after treatment of stationary phase cells with Cd(II). A biofilm forms on the cell surface, Cd(II) adsorbs, and is reduced to Cd (0) in the form of nanoscale particles. The genome of strain MBR was sequenced, annotated and analyzed. We identified various genes potentially related to cadmium resistance, transport and metabolism. Analysis of the strain MBR genome is helpful to explore the mechanism of Cd(II) resistance, and can provide new ideas for cadmium pollution control.

A new mercury-accumulating Mucor hiemalis strain EH8 from cold sulfidic spring water biofilms

Here, we report about a unique aquatic fungus Mucor hiemalisEH8 that can remove toxic ionic mercury from water by intracellular accumulation and reduction into elemental mercury (Hg0 ). EH8 was isolated from a microbial biofilm grown in sulfidic-reducing spring water sourced at a Marching's site located downhill from hop cultivation areas with a history of mercury use. A thorough biodiversity survey and mercury-removal function analyses were undertaken in an area of about 200 km2 in Bavaria (Germany) to find the key biofilm and microbe for mercury removal. After a systematic search using metal removal assays we identified Marching spring's biofilm out of 18 different sulfidic springs' biofilms as the only one that was capable of removing ionic Hg from water. EH8 was selected, due to its molecular biological identification as the key microorganism of this biofilm with the capability of mercury removal, and cultivated as a pure culture on solid and in liquid media to produce germinating sporangiospores. They removed 99% of mercury from water within 10-48 h after initial exposure to Hg(II). Scanning electron microscopy demonstrated occurrence of intracellular mercury in germinating sporangiospores exposed to mercury. Not only associated with intracellular components, but mercury was also found to be released and deposited as metallic-shiny nanospheres. Electron-dispersive x-ray analysis of such a nanosphere confirmed presence of mercury by the HgMα peak at 2.195 keV. Thus, a first aquatic eukaryotic microbe has been found that is able to grow even at low temperature under sulfur-reducing conditions with promising performance in mercury removal to safeguard our environment from mercury pollution.

Mercury-mediated cross-resistance to tellurite in Pseudomonas spp. isolated from the Chilean Antarctic territory

Mercury salts and tellurite are among the most toxic compounds for microorganisms on Earth.

High quality draft genome sequence of the heavy metal resistant bacterium Halomonas zincidurans type strain B6(T)

Halomonas zincidurans strain B6(T) was isolated from a deep-sea heavy metal rich sediment from the South Atlantic Mid-Ocean Ridge. The strain showed significant resistance to heavy metals, especially to zinc. Here we describe the genome sequence and annotation, as well as the features, of the organism. The genome contains 3,325 protein-coding genes (2,848 with predicted functions), 61 tRNA genes and 6 rRNA genes. H. zincidurans strain B6(T) encodes 31 genes related to heavy metal resistance. And HGT may play an important role in its adaption to the heavy metal rich environment. H. zincidurans strain B6(T) may have potential applications in the bioremediation of heavy metal-contaminated environments.

A conservative region of the mercuric reductase gene (mera) as a molecular marker of bacterial mercury resistance

The most common bacterial mercury resistance mechanism is based on the reduction of Hg(II) to Hg(0), which is dependent of the mercuric reductase enzyme (MerA) activity. The use of a 431 bp fragment of a conservative region of the mercuric reductase (merA) gene was applied as a molecular marker of this mechanism, allowing the identification of mercury resistant bacterial strains.

Functioning of the mercury resistance operon at extremely high Hg(II) loads in a chemostat: A proteome analysis

The transformation of extremely high concentrations of ionic mercury (up to 500 mg L(-1)) was investigated in a chemostat for two mercury-resistant Pseudomonas putida strains, the sediment isolate Spi3 carrying a regulated mercury resistance (mer) operon, and the genetically engineered strain KT2442Colon, two colonsmer73 expressing the mer operon constitutively. Both strains reduced Hg(II) with an efficiency of 99.9% even at the maximum load, but the concentration of particle bound mercury in the chemostat increased strongly. A proteome analysis using two-dimensional gel electrophoresis and mass spectrometry (2-DE/MS) showed constant expression of the MerA and MerB proteins in KT2442Colon, two colonsmer73 as expected, while in Spi3 expression of both proteins was strongly dependent on the Hg(II) concentration. The total cellular proteome of the two strains showed very little changes at high Hg(II) load. However, certain cellular responses of the two strains were identified, especially in membrane-related transport proteins. In Spi3, an up to 45-fold strong induction of a cation efflux transporter was observed, accompanied by a drastic downregulation (106-fold) of an outer membrane porin. In such a way, the cell complemented the highly specific mercury resistance mechanism with a general detoxification response. No indication of a higher demand on energy metabolism could be found for both strains.

Analysis of mercuric reductase (merA) gene diversity in an anaerobic mercury-contaminated sediment enrichment

The reduction of ionic mercury to elemental mercury by the mercuric reductase (MerA) enzyme plays an important role in the biogeochemical cycling of mercury in contaminated environments by partitioning mercury to the atmosphere. This activity, common in aerobic environments, has rarely been examined in anoxic sediments where production of highly toxic methylmercury occurs. Novel degenerate PCR primers were developed which span the known diversity of merA genes in Gram-negative bacteria and amplify a 285 bp fragment at the 3' end of merA. These primers were used to create a clone library and to analyse merA diversity in an anaerobic sediment enrichment collected from a mercury-contaminated site in the Meadowlands, New Jersey. A total of 174 sequences were analysed, representing 71 merA phylotypes and four novel MerA clades. This first examination of merA diversity in anoxic environments suggests an untapped resource for novel merA sequences.

Monitoring of microbial metal transformations in the environment

The biotransformation of metals is an exciting, developing strategy to treat metal contamination, especially in environments that are not accessible to other remediation technologies. However, our ability to benefit from these strategies hinges on our ability to monitor these transformations in the environment. This involves monitoring metals in both solid and aqueous samples, distinguishing between different chemical states, and obtaining information on the activities of specific microbial taxa in communities that inhabit the treated site. Accomplishing these goals requires cooperation among scientists from various disciplines and would benefit from both new, innovative approaches and the tailoring of established methods to control metal mobility in the environment.