Metal-resistant Species Research Articles

Multiple metal(loid) contamination reshaped the structure and function of soil archaeal community

Archaea are important participants in biogeochemical cycles of metal(loid)-polluted ecosystems, whereas archaeal structure and function in response to metal(loid) contamination remain poorly understood. Here, the effects of multiple metal(loid) pollution on the structure and function of archaeal communities were investigated in three zones within an abandoned sewage reservoir. We found that the high-contamination zone (Zone I) had higher archaeal diversity but a lower habitat niche breadth, relative to the mid-contamination zone (Zone II) and low-contamination zone (Zone III). Particularly, metal-resistant species represented by potential methanogens were markedly enriched in Zone I (cumulative relative abundance: 32.24%) compared to Zone II (1.93%) and Zone III (0.10%), and closer inter-taxon connections and higher network complexity (based on node number, edge number, and degree) were also observed compared to other zones. Meanwhile, the higher abundances of potential metal-resistant and methanogenic functions in Zone I (0.24% and 9.24%, respectively) than in Zone II (0.08% and 7.52%) and Zone III (0.01% and 1.03%) suggested archaeal functional adaptation to complex metal(loid) contamination. More importantly, six bioavailable metal(loid)s (titanium, tin, nickel, chromium, cobalt, and zinc) were the main contributors to archaeal community variations, and metal(loid) pollution reinforced the role of deterministic processes, particularly homogeneous selection, in the archaeal community assembly. Overall, this study provides the first integrated insight into the survival strategies of archaeal communities under multiple metal(loid) contamination, which will be of significant guidance for future bioremediation and environmental governance of metal(loid)-contaminated environments.

High Redox Status as the Basis for Heavy Metal Tolerance of Sesuvium portulacastrum L. Inhabiting Contaminated Soil in Jeddah, Saudi Arabia.

Because sewage sludge is contaminated with heavy metals, its disposal in the soil may pose risks to the ecosystem. Thus, heavy metal remediation is necessary to reduce the associated risks. The goal of this research is to introduce a heavy metal resistant species and to assess its phytoremediation, oxidative damage markers and stress tolerance mechanisms. To this end, field research was done to compare the vegetation of polluted sites to that of a healthy site. We found 42 plant species identified in the study, Sesuvium portulacastrum L. was chosen because of its high relative density (10.3) and maximum frequency (100 percent) in the most contaminated areas. In particular, S. portulacastrum plants were characterized by strong Cu, Ni, and As uptake. At the organ level, to control growth reduction and oxidase damage, particularly in roots, increased detoxification (e.g., metallothionein, phytochelatins) and antioxidants mechanisms (e.g., tocopherols, glutathione, peroxidases). On the other hand, flavonoids content and the activity of glutathione-S transferase, glutathione reductase and dehydroascorbate reductase were increased manly in the shoots. These biochemical markers can be applied to select tolerance plant species grown under complex heavy metal contamination. Our findings also introduced S. portulacastrum to reduce soil contamination0associated risks, making the land resource available for agricultural production.

Bioavailable metal(loid)s and physicochemical features co-mediating microbial communities at combined metal(loid) pollution sites

Heavy metal contamination poses considerable threats to various ecosystems, yet little is known about the assembly and adaptation of microbial communities at sites with combined heavy metal(loid) pollution. Here, we examined metal(loid) pollutants and bacterial communities in three zones (Zones Ⅰ, Ⅱ, and Ⅲ) of an abandoned sewage reservoir with different usage years. The contamination level of multiple metal(loid)s was higher in Zone Ⅰ than in the other zones, and arsenic (As), zinc (Zn), selenium (Se), copper (Cu), tin (Sn), molybdenum (Mo), antimony (Sb), cadmium (Cd), lead (Pb), thallium (Tl), and nickel (Ni) were the major contaminants (pollution load index > 1). Bioavailable forms of titanium (Ti), chromium (Cr), Sn, and cobalt (Co) played essential roles in shaping the microbial structure, and physicochemical properties, especially organic matter (OM) and pH, also mediated the microbial diversity and composition in the metal(loid) contaminated zones. Metal–microbe interactions and heatmap analysis revealed that the bioavailability of metal(loid)s promoted the niche partitioning of microbial species. Metal-resistant species were abundant in Zone Ⅰ that had the highest metal-contaminated level, whereas metal-sensitive species prevailed in Zone Ⅲ that had the lowest pollution level. The bioavailable metal(loid)s rather than physicochemical and spatial variables explained a larger portion of the variance in the microbial community, and the homogeneous selection was the dominant ecological process driving the assembly of the microbial community. Overall, our study highlighted the importance of metal(loid) bioavailability in shaping microbial structure, future bioremediation, and environmental management of metal(loid) contaminated sites.

Azolla filiculoides L. as a source of metal-tolerantmicroorganisms.

The metal hyperaccumulator Azolla filiculoides is accompanied by a microbiome potentially supporting plant during exposition to heavy metals. We hypothesized that the microbiome exposition to selected heavy metals will reveal metal tolerant strains. We used Next Generation Sequencing technique to identify possible metal tolerant strains isolated from the metal-treated plant (Pb, Cd, Cr(VI), Ni, Au, Ag). The main dominants were Cyanobacteria and Proteobacteria constituting together more than 97% of all reads. Metal treatment led to changes in the composition of the microbiome and showed significantly higher richness in the Pb-, Cd- and Cr-treated plant in comparison with other (95-105 versus 36-44). In these treatments the share of subdominant Actinobacteria (0.4-0.8%), Firmicutes (0.5-0.9%) and Bacteroidetes (0.2-0.9%) were higher than in non-treated plant (respectively: 0.02, 0.2 and 0.001%) and Ni-, Au- and Ag-treatments (respectively: <0.4%, <0.2% and up to 0.2%). The exception was Au-treatment displaying the abundance 1.86% of Bacteroidetes. In addition, possible metal tolerant genera, namely: Acinetobacter, Asticcacaulis, Anabaena, Bacillus, Brevundimonas, Burkholderia, Dyella, Methyloversatilis, Rhizobium and Staphylococcus, which form the core microbiome, were recognized by combining their abundance in all samples with literature data. Additionally, the presence of known metal tolerant genera was confirmed: Mucilaginibacter, Pseudomonas, Mycobacterium, Corynebacterium, Stenotrophomonas, Clostridium, Micrococcus, Achromobacter, Geobacter, Flavobacterium, Arthrobacter and Delftia. We have evidenced that A. filiculoides possess a microbiome whose representatives belong to metal-resistant species which makes the fern the source of biotechnologically useful microorganisms for remediation processes.

Metal pollution affects both native and non-indigenous biofouling recruitment in a subtropical island system

Hull fouling has been a driving force behind the development of most modern marine antifouling coatings that mainly contain copper based biocides to inhibit growth of fouling organisms. Despite these efforts, several non-indigenous species continue to be transferred via hull-fouling worldwide. In this study we designed a disturbance gradient with three commercial antifouling paints applied to PVC settling plates with different concentrations of copper oxide and allowed colonization of fouling communities in four marinas located at the Madeira Archipelago (NE Atlantic). Overall, the antifouling treatments were effective in decreasing the diversity of fouling communities and spatial variability across marinas was observed. Increasing exposure to metal pollutants decreases both species cover and total diversity, independently of their native or NIS condition. However, evidences found suggest that long-term effects of copper based antifouling coatings can be modulated by metal-resistant species allowing a secondary substrate for the epibiosis of other species to establish.

Biological role in the transformation of platinum-group mineral grains

Platinum-group elements are strategically important metals. Finding new deposits is becoming increasingly difficult owing to our limited understanding of the processes that affect their mobility in surface environments. Microorganisms have been shown to promote the mobility of metals around ore deposits. Here we show that microorganisms influence the mobility of platinum-group elements in mineral grains collected from Brazil, Australia and Colombia. Scanning electron microscopy showed biofilms covering the platinum-group mineral grains. The biofilms contained abundant platinum-group element nanoparticles and microcrystalline aggregates, and were dominated by Proteobacteria, many of which were closely related to known metal-resistant species. Some platinum-group mineral grains contained carbon, nitrogen, sulfur, selenium and iodine, suggesting the grains may be biogenic in origin. Molecular analyses show that Brazilian platinum–palladium grains hosted specific bacterial communities, which were different in composition from communities associated with gold grains, or communities in surrounding soils and sediments. Nano-phase metallic platinum accumulated when a metallophillic bacterium was incubated with a percolating platinum-containing medium, suggesting that biofilms can cause the precipitation of mobile platinum complexes. We conclude that biofilms are capable of forming or transforming platinum-group mineral grains, and may play an important role for platinum-group element dispersion and re-concentration in surface environments.

Recovery potential of periphytic biofilms translocated in artificial streams after industrial contamination (Cd and Zn)

Metal wastes can significantly disturb aquatic communities, particularly photosynthetic organisms, the main primary producers in freshwater running ecosystems. In this study, biofilms and diatoms were used as bioindicators to characterize the kinetics of biofilm recovery. An experimental decontamination study was conducted under laboratory conditions, after biofilm colonisation at a site subject to discharge of industrial metals (Zn and Cd) and in parallel at an upstream site, metal-free, considered as a control. After 24 days of colonisation, biofilms were translocated and maintained in the laboratory for 56 days under clean conditions (control and decontamination) or metal contamination. Various tests were conducted from the community level--measures of metal bioaccumulation, cell densities and taxonomic investigations, to the individual level--measures of teratological forms. After 56 days of decontamination, Zn and Cd concentrations in decontaminated biofilms showed a sharp decline, respectively ranging from 6.7 ± 2 to 4 ± 2.5 mg Zn g⁻¹ DW and from 207.6 ± 24.5 to 45.4 ± 9.9 μg Cd g⁻¹ DW. However, at the end of the experiment bioaccumulations remained significantly higher than concentrations in control biofilms. Despite a diatom evolution in biofilm assemblages, taxonomic inventories did not demonstrate a complete restoration of diatom communities in biofilms under decontamination conditions compared with controls, since metal-resistant species initially present after colonisation at the contaminated site, such as Eolimna minima, persisted in high abundance in decontaminated biofilms. Biofilms kept under metal pressure showed very high bioaccumulation capacities and a sharp decline of species diversity which allowed identification of some resistant species. Regarding these first results on the behaviour of diatom biofilms under experimental decontamination conditions, improvement of the natural hydrosystem's chemical state appears quickly, but an eventual return to good ecological status appears delayed, with the persistence of metal-tolerant species even after 56 days.

Remediation of a watershed contaminated by heavy metals: A 2-year field biomonitoring of periphytic biofilms

This study focuses on an industrial contamination site subjected to remediation processes since 2007 in the Riou-Mort watershed (southwest France). The purpose was to assess the first impacts of remediation on periphytic biofilms, and was performed during two years of biomonitoring. Periphytic biofilms were collected on glass slides immersed 24days at different sites along the contamination gradient for 12 colonisation cycles. Metal contaminations (Cd and Zn) were analysed in biofilms and the evolution of diatom communities was assessed, integrating teratology quantifications. Despite remediation work initiated at the industrial site, this study demonstrated the persistence of metal contamination in water, as well as in biofilms. In addition, our data, showed that the remediation process was initially marked by an increase in metal contamination in the river, with increasing diatom community shifts. Metal-contaminated biofilms presented decreasing species diversities and were dominated by metal-resistant species such as Eolimna minima, whom abundances increased in 2010 reaching 57.2±10%. No significant decrease in metal accumulation was observed and total Cd content in biofilms collected downstream the industrial site ranged from 772.7±88 in July 2009 to 636.9±20μg/gDW in July 2010. Results obtained on artificial substrates were compared with those of natural substrates and showed similar diatom communities and abundances of deformed diatoms but lower diversities. This ensured that glass slide subtrates gave a good representation of periphytic biofilm health. Finally, results were compared to studies performed before the remediation process and this did not reveal a decrease of metal accumulation in biofilms nor shifts in taxonomic composition of the communities, rather the remaining dominance of metal resistant species such as E. minima was confirmed.

Draft Genome of Streptomyces zinciresistens K42, a Novel Metal-Resistant Species Isolated from Copper-Zinc Mine Tailings

A draft genome sequence of Streptomyces zinciresistens K42, a novel Streptomyces species displaying a high level of resistance to zinc and cadmium, is presented here. The genome contains a large number of genes encoding proteins predicted to be involved in conferring metal resistance. Many of these genes appear to have been acquired through horizontal gene transfer.

Toxic heavy metal biosorption by some marine bacteria isolated from the sediments of industrial effluents of Iligan Bay

Heavy metal-resistant marine bacteria were isolated from the sediments of Iligan Bay near the effluents outlets of certain factories. Isolation was done using marine agar fortified with corresponding different heavy metal concentrations. Isolates were grouped using their morphological and colonial growth characteristics. Among the purified isolates(61), 19 were cadmium-resistant, 29 were lead-resistant and 13 were mercury-resistant. These isolates were tested for their absorptive capability using marine broth added with metal ions: 23.20 µg of Cd, 250.24 µg of Pb and 495.66 µg of Hg, and consequently analyzed using Atomic Absorption Spectrophotometric(AAS) method. From these isolates, 10 heavy metal-resistant species with relatively high absorptive efficiency were identified using conventional method and API 20E Test Kit. Out of ten isolates, 3 were Gram-positive and 7 were Gram-negative rods. All Gram-positive bacteria belong to the genus Bacillus and were found to absorb lead metals at 94% absorptive efficiency. However, Enterobacter sp. 2 had the highest absorptive efficiency for Cd at 99% among Gram negative bacteria followed by Chryseomonas sp. 2 with 96% biosorption. Furthermore, among the mercury resistant isolates, Pseudomonas sp. had the highest absorptive efficiency at 79%. Only those heavy metal-resistant isolates which exhibited the highest absorptive efficiency were able to form a zone of growth promotion around a heavy metal-containing filter paper disk which suggests that these bacteria have accumulated heavy metals in their cells. The presence of heavy metal-resistant bacteria is helpful in cleaning up or remediating metal contaminated environments released from industrial effluents.

Metal stress on the plankton communities of Sado River (Portugal)

The effects of heavy metals on the structure of phytoplankton and zooplankton communities were determined in Sado River, Portugal, during the period of highest production (summer). Two tributaries, receiving wastes from pyrite mines, enter the river and gave rise, in the middle reaches, to dissolved metal concentrations up to 88 μg l −1 Cu, 2.6 μg l −1 Cd and 1800 μg l −1 Zn. At the most polluted sites phytoplankton responded mainly by a shift towards metal resistant species: dominant species such as Rhodomonas minuta, Synedra ulna, Crucigenia tetrapedia and Stephanodiscus hantzschii were replaced by Gomphonema parvulum, Scenedesmus armatus and Nitzschia frustulum, while the total algal standing crop was not significantly affected. In contrast, zooplankton displayed a strong reduction in the abundance of major groups (40–100%), species richness (59%) and diversity (58–75%), and only a few taxa, namely Acanthocyclops robustus, Arcella vulgaris, Philodina sp., seemed to tolerate high metal concentrations. At the lower river reaches, where metal contamination decreased substantially, a recovery in species composition and abundance was observed for both plankton communities.

Comparison of cadmium-binding protein induction among mayfly larvae of heavy metal resistant (Baetis thermicus) and susceptible species (B. yoshinensis and B. sahoensis)

1. The mayfly larvae of a heavy metal resistant species ( Baetis thermicus) and two heavy metal susceptible species ( B. yoshinensis and B. sahoensis) were exposed to cadmium at a concentration of 10 μg/1 and the comparative induction of cadmium-binding protein was correlated to their susceptibility to the metal. 2. Amounts of cadmium accumulated in the larvae were increased linearly depending on the duration of exposure. However, there was little difference in the cadmium concentration in each species. 3. Cadmium-binding protein was induced only in the larvae of resistant species ( B. thermicus). 4. Copper and zinc concentrations in the two susceptible larvae were decreased by cadmium exposure, while zinc but not copper concentrations were increased in the resistant larvae.