Cadmium specific proteomic responses of a highly resistantPseudomonas aeruginosasan ai

Quantification of the effect of biochar application on heavy metals in paddy systems: Impact, mechanisms and future prospects

Biochar (BC) has shown great potential in remediating heavy metal(loid)s (HMs) contamination in paddy fields. Variation in feedstock sources, pyrolysis temperatures, modification methods, and application rates of BC can result in great changes in its effects on HM bioavailability and bioaccumulation in soil-rice systems and remediation mechanisms. Meanwhile, there is a lack of application guidelines for BC with specific properties and application rates when targeting rice fields contaminated with certain HMs. To elucidate this topic, this review focuses on i) the effects of feedstock type, pyrolysis temperature, and modification method on the properties of BC; ii) the changes in bioavailability and bioaccumulation of HMs in soil-rice systems applying BC with different feedstocks, pyrolysis temperatures, modification methods, and application rates; and iii) exploration of potential remediation mechanisms for applying BC to reduce the mobility and bioaccumulation of HMs in rice field systems. In general, the application of Fe/Mn modified organic waste (OW) derived BC for mid-temperature pyrolysis is still a well-optimized choice for the remediation of HM contamination in rice fields. From the viewpoint of remediation efficiency, the application rate of BC should be appropriately increased to immobilize Cd, Pb, and Cu in rice paddies, while the application rate of BC for immobilizing As should be <2.0 % (w/w). The mechanism of remediation of HM-contaminated rice fields by applying BC is mainly the direct adsorption of HMs by BC in soil pore water and the mediation of soil microenvironmental changes. In addition, the application of Fe/Mn modified BC induced the formation of iron plaque (IP) on the root surface of rice, which reduced the uptake of HM by the plant. Finally, this paper describes the prospects and challenges for the extension of various BCs for the remediation of HM contamination in paddy fields and makes some suggestions for future development.

Proteomic analysis to unravel the biochemical mechanisms triggered by Bacillus toyonensis SFC 500-1E under chromium(VI) and phenol stress

Bacillus toyonensis SFC 500-1E is a member of the consortium SFC 500-1 able to remove Cr(VI) and simultaneously tolerate high phenol concentrations. In order to elucidate mechanisms utilized by this strain during the bioremediation process, the differential expression pattern of proteins was analyzed when it grew with or without Cr(VI) (10 mg/L) and Cr(VI) + phenol (10 and 300 mg/L), through two complementary proteomic approaches: gel-based (Gel-LC) and gel-free (shotgun) nanoUHPLC-ESI-MS/MS. A total of 400 differentially expressed proteins were identified, out of which 152 proteins were down-regulated under Cr(VI) and 205 up-regulated in the presence of Cr(VI) + phenol, suggesting the extra effort made by the strain to adapt itself and keep growing when phenol was also added. The major metabolic pathways affected include carbohydrate and energetic metabolism, followed by lipid and amino acid metabolism. Particularly interesting were also ABC transporters and the iron-siderophore transporter as well as transcriptional regulators that can bind metals. Stress-associated global response involving the expression of thioredoxins, SOS response, and chaperones appears to be crucial for the survival of this strain under treatment with both contaminants. This research not only provided a deeper understanding of B. toyonensis SFC 500-1E metabolic role in Cr(VI) and phenol bioremediation process but also allowed us to complete an overview of the consortium SFC 500-1 behavior. This may contribute to an improvement in its use as a bioremediation strategy and also provides a baseline for further research.

Functional response of Acinetobacter guillouiae SFC 500-1A to tannery wastewater as revealed by a complementary proteomic approach

Acinetobacter guillouiae SFC 500-1 A is a promising candidate for the bioremediation of tannery wastewater. In this study, we applied shotgun proteomic technology in conjunction with a gel-based assay (Gel-LC) to explore the strain's intracellular protein profile when grown in tannery wastewater as opposed to normal culture conditions. A total of 1775 proteins were identified, 52 of which were unique to the tannery wastewater treatment. Many of them were connected to the degradation of aromatic compounds and siderophore biosynthesis. On the other hand, 1598 proteins overlapped both conditions but were differentially expressed in each. Those that were upregulated in wastewater (109) were involved in the processes mentioned above, as well as in oxidative stress mitigation and intracellular redox state regulation. Particularly interesting were the downregulated proteins under the same treatment (318), which were diverse but mainly linked to the regulation of basic cellular functions (replication, transcription, translation, cell cycle, and wall biogenesis); metabolism (amino acids, lipids, sulphate, energetic processes); and other more complex responses (cell motility, exopolysaccharide production, biofilm formation, and quorum sensing). The findings suggest that SFC 500-1 A engages in survival and stress management strategies to cope with the toxic effects of tannery wastewater, and that such strategies may be mostly oriented at keeping metabolic processes to a minimum. Altogether, the results might be useful in the near future to improve the strain's effectiveness if it will be applied for bioremediation.

A comprehensive proteomics analysis of the response of Pseudomonas aeruginosa to nanoceria cytotoxicity

The increased commercial use and spread of nanoceria raises concerns about the risks associated with its effects on living organisms. Although Pseudomonas aeruginosa may be ubiquitous in nature, it is largely found in locations closely linked with human activity. P. aeruginosa san ai was used as a model organism for a deeper understanding of the interaction between biomolecules of the bacteria with this intriguing nanomaterial. A comprehensive proteomics approach along with analysis of altered respiration and production of targeted/specific secondary metabolites was conducted to study the response of P. aeruginosa san ai to nanoceria. Quantitative proteomics found that proteins associated with redox homeostasis, biosynthesis of amino acids, and lipid catabolism were upregulated. Proteins from outer cellular structures were downregulated, including transporters responsible for peptides, sugars, amino acids and polyamines, and the crucial TolB protein of the Tol-Pal system, required for the structural formation of the outer membrane layer. In accordance with the altered redox homeostasis proteins, an increased amount of pyocyanin, a key redox shuttle, and the upregulation of the siderophore, pyoverdine, responsible for iron homeostasis, were found. Production of extracellular molecules, e.g. pyocyanin, pyoverdine, exopolysaccharides, lipase, and alkaline protease, was significantly increased in P. aeruginosa san ai exposed to nanoceria. Overall, nanoceria at sublethal concentrations induces profound metabolic changes in P. aeruginosa san ai and provokes increased secretion of extracellular virulence factors, revealing the powerful influence this nanomaterial has on the vital functions of the microorganism.

Pseudomonas in environmental bioremediation of hydrocarbons and phenolic compounds- key catabolic degradation enzymes and new analytical platforms for comprehensive investigation

Pollution of the environment with petroleum hydrocarbons and phenolic compounds is one of the biggest problems in the age of industrialization and high technology. Species of the genus Pseudomonas, present in almost all hydrocarbon-contaminated areas, play a particular role in biodegradation of these xenobiotics, as the genus has the potential to decompose various hydrocarbons and phenolic compounds, using them as its only source of carbon. Plasticity of carbon metabolism is one of the adaptive strategies used by Pseudomonas to survive exposure to toxic organic compounds, so a good knowledge of its mechanisms of degradation enables the development of new strategies for the treatment of pollutants in the environment. The capacity of microorganisms to metabolize aromatic compounds has contributed to the evolutionally conserved oxygenases. Regardless of the differences in structure and complexity between mono- and polycyclic aromatic hydrocarbons, all these compounds are thermodynamically stable and chemically inert, so for their decomposition, ring activation by oxygenases is crucial. Genus Pseudomonas uses several upper and lower metabolic pathways to transform and degrade hydrocarbons, phenolic compounds, and petroleum hydrocarbons. Data obtained from newly developed omics analytical platforms have enormous potential not only to facilitate our understanding of processes at the molecular level but also enable us to instigate and monitor complex biodegradations by Pseudomonas. Biotechnological application of aromatic metabolic pathways in Pseudomonas to bioremediation of environments polluted with crude oil, biovalorization of lignin for production of bioplastics, biofuel, and bio-based chemicals, as well as Pseudomonas-assisted phytoremediation are also considered.

Effect of Biochar on Metal Distribution and Microbiome Dynamic of a Phytostabilized Metalloid-Contaminated Soil Following Freeze-Thaw Cycles

In the present paper the effectiveness of biochar-aided phytostabilization of metal/metalloid-contaminated soil under freezing-thawing conditions and using the metal tolerating test plant Lolium perenne L. is comprehensively studied. The vegetative experiment consisted of plants cultivated for over 52 days with no exposure to freezing-thawing in a glass greenhouse, followed by 64 days under freezing-thawing in a temperature-controlled apparatus and was carried out in initial soil derived from a post-industrial urban area, characterized by the higher total content of Zn, Pb, Cu, Cr, As and Hg than the limit values included in the classification provided by the Regulation of the Polish Ministry of Environment. According to the substance priority list published by the Toxic Substances and Disease Registry Agency, As, Pb, and Hg are also indicated as being among the top three most hazardous substances. The initial soil was modified by biochar obtained from willow chips. The freeze-thaw effect on the total content of metals/metalloids (metal(-loid)s) in plant materials (roots and above-ground parts) and in phytostabilized soils (non- and biochar-amended) as well as on metal(-loid) concentration distribution/redistribution between four BCR (community bureau of reference) fractions extracted from phytostabilized soils was determined. Based on metal(-loid)s redistribution in phytostabilized soils, their stability was evaluated using the reduced partition index (Ir). Special attention was paid to investigating soil microbial composition. In both cases, before and after freezing-thawing, biochar increased plant biomass, soil pH value, and metal(-loid)s accumulation in roots, and decreased metal(-loid)s accumulation in stems and total content in the soil, respectively, as compared to the corresponding non-amended series (before and after freezing-thawing, respectively). In particular, in the phytostabilized biochar-amended series after freezing-thawing, the recorded total content of Zn, Cu, Pb, and As in roots substantially increased as well as the Hg, Cu, Cr, and Zn in the soil was significantly reduced as compared to the corresponding non-amended series after freezing-thawing. Moreover, exposure to freezing-thawing itself caused redistribution of examined metal(-loid)s from mobile and/or potentially mobile into the most stable fraction, but this transformation was favored by biochar presence, especially for Cu, Pb, Cr, and Hg. While freezing-thawing greatly affected soil microbiome composition, biochar reduced the freeze-thaw adverse effect on bacterial diversity and helped preserve bacterial groups important for efficient soil nutrient conversion. In biochar-amended soil exposed to freezing-thawing, psychrotolerant and trace element-resistant genera such as Rhodococcus sp. or Williamsia sp. were most abundant.

Pseudomonas sp. TCd-1 significantly alters the rhizosphere bacterial community of rice in Cd contaminated paddy field

Cadmium (Cd) pollution of paddy soils is one of the main concerns causing food security and environmental problems. Microbial bioremediation is an effective and eco-friendly measure that uses microbes to reduce Cd accumulation in crops. Additionally, rhizosphere bacterial communities also act essential roles in crop tolerance of heavy metals. However, the effects of inoculations with Cd resistant bacteria on crop rhizosphere bacterial communities under Cd exposure are largely unknown. In this study, we used high-throughput 16S rRNA gene sequencing technologies to explore the community structure and co-occurrence network of the rhizosphere bacterial communities associated with the rice crop under different Cd treatments and the application of Cd-tolerant strain Pseudomonas sp. TCd-1. We found that the strain TCd-1 both significantly reduced the rhizobacterial alpha diversity and changed the beta diversity. PERMANOVA and NMDS analysis showed that Cd stress and TCd-1 strain could act as strong environmental filters resulting in observable differentiation of rhizobacterial community composition among different groups. In addition, RDA results indicated that the rhizosphere pH, root Cd content, catalase (CAT), urease (URE), gibberellic acid (GA3) exert significant association with rhizosphere bacterial assembly. PICRUSt analysis revealed that the TCd-1 strain improved the metabolic capacity of rhizosphere bacteria under Cd stress. Furthermore, co-occurrence network topological features and keystone taxa also varied among different groups. This study could provide necessary insights into developing an efficient bioremediation and safe production of rice crops in Cd contaminated paddy fields with the application of Pseudomonas sp. TCd-1 strain, as well as advance our understanding of the principles of rhizosphere bacterial community assembly under Cd stress.

A study of the flexibility of the carbon catabolic pathways of extremophilic P. aeruginosa san ai exposed to benzoate versus glucose as sole carbon sources by multi omics analytical platform

Polyextremophilic, hydrocarbonoclastic Pseudomonas aeruginosa san ai can survive under extreme environmental challenges in the presence of a variety of pollutants such as organic solvents and hydrocarbons, particularly aromatics, heavy metals, and high pH. To date, the metabolic plasticity of the extremophilic P. aeruginosa, has not been sufficiently studied in regard to the effect of changing carbon sources. Therefore, the present study explores the carbon metabolic pathways of polyextremophilic P. aeruginosa san ai grown on sodium benzoate versus glucose and its potential for aromatic degradation. P. aeruginosa san ai removed/metabolised nearly 430 mg/L of benzoate for 48 h, demonstrating a high capacity for aromatic degradation. Comparative functional proteomics, targeted metabolomics and genomics analytical approaches were employed to study the carbon metabolism of the P. aeruginosa san ai. Functional proteomic study of selected enzymes participating in the β-ketoadipate and the Entner-Doudoroff pathways revealed a metabolic reconfiguration induced by benzoate compared to glucose. Metabolome analysis implied the existence of both catechol and protocatechuate branches of the β-ketoadipate pathway. Enzymatic study of benzoate grown cultures confirmed the activity of the ortho- catechol branch of the β-ketoadipate pathway. Even high concentrations of benzoate did not show increased stress protein synthesis, testifying to its extremophilic nature capable of surviving in harsh conditions. This ability of Pseudomonas aeruginosa san ai to efficiently degrade benzoate can provide a wide range of use of this strain in environmental and agricultural application.

Unraveling the complex regulatory networks in biofilm formation in bacteria and relevance of biofilms in environmental remediation

Biofilms are assemblages of bacteria embedded within a matrix of extracellular polymeric substances (EPS) attached to a substratum. The process of biofilm formation is a complex phenomenon regulated by the intracellular and intercellular signaling systems. Various secondary messenger molecules such as cyclic dimeric guanosine 3',5'-monophosphate (c-di-GMP), cyclic adenosine 3',5'-monophosphate (cAMP), and cyclic dimeric adenosine 3',5'-monophosphate (c-di-AMP) are involved in complex signaling networks to regulate biofilm development in several bacteria. Moreover, the cell to cell communication system known as Quorum Sensing (QS) also regulates biofilm formation via diverse mechanisms in various bacterial species. Bacteria often switch to the biofilm lifestyle in the presence of toxic pollutants to improve their survivability. Bacteria within a biofilm possess several advantages with regard to the degradation of harmful pollutants, such as increased protection within the biofilm to resist the toxic pollutants, synthesis of extracellular polymeric substances (EPS) that helps in the sequestration of pollutants, elevated catabolic gene expression within the biofilm microenvironment, higher cell density possessing a large pool of genetic resources, adhesion ability to a wide range of substrata, and metabolic heterogeneity. Therefore, a comprehensive account of the various factors regulating biofilm development would provide valuable insights to modulate biofilm formation for improved bioremediation practices. This review summarizes the complex regulatory networks that influence biofilm development in bacteria, with a major focus on the applications of bacterial biofilms for environmental restoration.

Impact of Tellurite on the Metabolism of Paenibacillus pabuli AL109b With Flagellin Production Explaining High Reduction Capacity

Tellurium (Te) is a metalloid with scarce and scattered abundance but with an increased interest in human activity for its uses in emerging technologies. As is seen for other metals and metalloids, the result of mining activity and improper disposal of high-tech devices will lead to niches with increased abundance of Te. This metalloid will be more available to bacteria and represent an increasing selective pressure. This environmental problem may constitute an opportunity to search for microorganisms with genetic and molecular mechanisms of microbial resistance to Te toxic anions. Organisms from Te-contaminated niches could provide tools for Te remediation and fabrication of Te-containing structures with added value. The objective of this study was to determine the ability of a high metal-resistant Paenibacillus pabuli strain ALJ109b, isolated from high metal content mining residues, to reduce tellurite ion, and to evaluate the formation of metallic tellurium by cellular reduction, isolate the protein responsible, and determine the metabolic response to tellurite during growth. P. pabuli ALJ109b demonstrated to be resistant to Te (IV) at concentrations higher than reported for its genus. It can efficiently remove soluble Te (IV) from solution, over 20% in 8 h of growth, and reduce it to elemental Te, forming monodisperse nanostructures, verified by scattering electron microscopy. Cultivation of P. pabuli ALJ109b in the presence of Te (IV) affected the general protein expression pattern, and hence the metabolism, as demonstrated by high-throughput proteomic analysis. The Te (IV)-induced metabolic shift is characterized by an activation of ROS response. Flagellin from P. pabuli ALJ109b demonstrates high Te (0) forming activity in neutral to basic conditions in a range of temperatures from 20°C to 37°C. In conclusion, the first metabolic characterization of a strain of P. pabuli response to Te (IV) reveals a highly resistant strain with a unique Te (IV) proteomic response. This strain, and its flagellin, display, all the features of potential tools for Te nanoparticle production.

Biological Synthesis of PbS, As3S4, HgS, CdS Nanoparticles using Pseudomonas aeruginosa and their Structural, Morphological, Photoluminescence as well as Whole Cell Protein Profiling Studies

Metal sulfide nanoparticles are semi-conductors that possess many applications in optics, optoelectronics and magnetic devices. There are physical and chemical methods for their synthesis but such methods involve toxic precursors as well as many obnoxious by-products. Hence, biological synthesis of metal sulfide nanoparticles are efficient enough to transform toxic metals to non-toxic ones. Pseudomonas aeruginosa, isolated from textile effluent and tolerant of high levels of heavy metals, was used for the green synthesis of metal sulfide (HgS, As3S4, CdS and PbS) nanoparticles. The optical, structural and morphological nature of metal sulfide nanoparticles was also determined. FTIR (Fourier Transform Infra-red) analysis showed spectral changes when P. aeruginosa was grown in medium containing heavy metals viz. Hg, As, Pb and Cd indicating that there are functional groups viz. carboxyl, hydroxyl, phosphate, amino and amide, that exists on the surface of the bacteria, thus facilitating binding of metals on its surface. The bacterial samples which were treated with different metals at different concentrations, were subjected to whole cell protein analysis using SDS-PAGE (Sodium dodecyl Sulphate- Polyacrylamide gel electrophoresis) and protein profiling. The total protein estimation revealed that there was an increase in the protein concentration in the presence of heavy metals and a significant change in the banding pattern was observed which showed induction of a set of proteins under heavy metal stress especially mercury.

Characterization of copper stress response in Fusarium tricinctum M6: A metal-resistant microorganism isolated from an acid mine drainage-affected environment

Acid mine drainage-affected environments are interesting microbial niches for the isolation of metal-resistant microorganisms. In this sense, the aim of the present work is to isolate and characterize metal-resistant microorganisms from sediments of an abandoned gold mine located in San Luis (Argentina). For these purposes, the metal removal capacity and the microelemental composition of the biomass exposed to metals were evaluated. Likewise, proteomic techniques were applied to understand the removal and resistance mechanisms. Fusarium tricinctum M6 was isolated and identified as tolerant to Cu(II), Fe(II) and Cr(VI). When faced with 40 µg mL-1 Cu(II), the growth was affected by 60% and the removal capacity was 30-35%. Copper was found uniformly distributed in the biomass (5.23% w/w) and variations in the proportion of other biomass constituent elements were detected. When exposed to Cu(II), F. tricinctum M6 showed differential expression of intra and extracellular proteins involved in different metabolic processes. A large number of proteins with metal ion binding sites were detected both at intra and extracellular levels. The results obtained in the present work indicated bioadsorption of the metal on the cell surface and an important readjustment of the protein expression to counteract the stress produced by Cu(II).

Bio-remediation approaches for alleviation of cadmium contamination in natural resources

Cadmium (Cd) is a harmful heavy metal that can cause potent environmental and health hazards at different trophic levels through food chain. Cd is relatively non-biodegradable and persists for a long time in the environment. Considering the potential toxicity and non-biodegradability of Cd in the environment as well as its health hazards, this is an urgent issue of international concern that needs to be addressed by implicating suitable remedial approaches. The current article specifically attempts to review the different biological approaches for remediation of Cd contamination in natural resources. Further, bioremediation mechanisms of Cd by microbes such as bacteria, fungi, algae are comprehensively discussed. Studies indicate that heavy metal resistant microbes can be used as suitable biosorbents for the removal of Cd (up to 90%) in the natural resources. Soil-to-plant transfer coefficient (TC) of Cd ranges from 3.9 to 3340 depending on the availability of metal to plants and also on the type of plant species. The potential phytoremediation strategies for Cd removal and the key factors influencing bioremediation process are also emphasized. Studies on molecular mechanisms of transgenic plants for Cd bioremediation show immense potential for enhancing Cd phytoremediation efficiency. Thus, it is suggested that nano-technological based integrated bioremediation approaches could be a potential futuristic path for Cd decontamination in natural resources. This review would be highly useful for the biologists, chemists, biotechnologists and environmentalists to understand the long-term impacts of Cd on ecology and human health so that potential remedial measures could be taken in advance.

Elucidation of crude siderophore extracts from supernatants of Pseudomonas sp. ZnCd2003 cultivated in nutrient broth supplemented with Zn, Cd, and Zn plus Cd

This research aimed to study siderophores secreted from Pseudomonas sp. PDMZnCd2003, a Zn/Cd tolerant bacterium. The effects of Zn and/or Cd stress were examined in nutrient broth to achieve the actual environmental conditions. Acid and alkali supernatants and liquid-liquid extraction with ethyl acetate and butanol were carried out to obtain crude extracts containing different amounts of the metals. The bacterial growth, UV-visible spectra of the supernatants and siderophore production indicated that the production of siderophores tended to be linked to primary metabolites. Pyocyanin was produced in all treatments, while pyoverdine was induced by stress from the metals, especially Cd. FT-IR spectra showed C=O groups and sulfur functional groups that were involved in binding with the metals. LC-MS revealed that pyocyanin, 1-hydroxy phenazine, pyoverdine, and pyochelin were present in the crude extracts. S K-edge XANES spectra showed that the main sulfur species in the extracts were the reduced forms of sulfide, thiol, and disulfide, and their oxidation states were affected by coordination with Zn and/or Cd. In addition, Zn K-edge EXAFS spectra and Cd K-edge EXAFS spectra presented Zn-O and Cd-O as coordination in the first shell, in case the extracts contained less metal. Although the mix O/S ligands had chelation bonding with Zn and Cd in the other extracts. For the role of S groups in pyochelin binding with the metals, this was the first report. The results of these experiments could be extended to Pseudomonas that respond to metal contaminated environments.

Cadmium and antibiotic-resistant Acinetobacter calcoaceticus strain STP14 reported from sewage treatment plant

A bacterium designated as strain STP14 was isolated from a sewage treatment plant and identified as Acinetobacter calcoaceticus based on 16S ribosomal RNA gene sequencing. Strain STP14 exhibited resistance to several metals such as mercury, cobalt, copper, nickel, lead, and cadmium. Among these metals, the bacterium showed maximum resistance to cadmium in concentration up to 1200 mg/L. The antimicrobial susceptibility test of A. calcoaceticus strain STP14 showed coresistance to all tested antibiotics except tigecycline and chloramphenicol for which 16 ± 1- and 15 ± 1-mm zone of inhibition was observed, respectively. The protein pattern of the crude cellular extract revealed substantial differences in protein bands of untreated control and cadmium treated A. calcoaceticus strain STP14 suggesting variable protein expression under cadmium stress. Metals and antibiotic resistance are increasing phenomenon and universal concern of public health. This study improves our understanding regarding the bacterial coresistance against metals and antibiotics and the possible emergence of multidrug resistance due to selective pressure and coselection in the metal polluted sewage sludge.

Metal-induced bacterial interactions promote diversity in river-sediment microbiomes

Anthropogenic metal contamination results in long-term environmental selective pressure with unclear impacts on bacterial communities, which comprise key players in ecosystem functioning. Since metal contamination poses serious toxicity and bioaccumulation issues, assessing their impact on environmental microbiomes is important to respond to current environmental and health issues. Despite elevated metal concentrations, the river sedimentary microbiome near the MetalEurop foundry (France) shows unexpected higher diversity compared with the upstream control site. In this work, a follow-up of the microbial community assembly during a metal contamination event was performed in microcosms with periodic renewal of the supernatant river water. Sediments of the control site were gradually exposed to a mixture of metals (Cd, Cu, Pb and Zn) in order to reach similar concentrations to MetalEurop sediments. Illumina sequencing of 16S rRNA gene amplicons was performed. Metal-resistant genes, czcA and pbrA, as well as IncP plasmid content, were assessed by quantitative PCR. The outcomes of this study support previous in situ observations showing that metals act as community assembly managers, increasing diversity. This work revealed progressive adaptation of the sediment microbiome through the selection of different metal-resistant mechanisms and cross-species interactions involving public good-providing bacteria co-occurring with the rest of the community.

Effect of bioaugmentation on digestate metal concentrations in anaerobic digestion of sewage sludge

This study examined the influence of bioaugmentation on metal concentrations (aluminum, cadmium, chromium, cobalt, copper, iron, lead, manganese, molybdenum, nickel and zinc) in anaerobically digested sewage sludge. To improve the digestion efficiency, bioaugmentation with a mixture of wild-living Archaea and Bacteria (MAB) from Yellowstone National Park, USA, was used. The total concentration of all metals was higher in the digestate than in the feedstock. During anaerobic digestion, the percent increase in the concentration of most of metals was slightly higher in the bioaugmented runs than in the un-augmented runs, but these differences were not statistically significant. However, the percent increase in cadmium and cobalt concentration was significantly higher in the bioaugmented runs than in the un-augmented runs. At MAB doses of 9 and 13% v/v, cadmium concentration in the digestate was 211 and 308% higher than in the feedstock, respectively, and cobalt concentration was 138 and 165%, respectively. Bioaugmentation increased over 4 times the percentage of Pseudomonas sp. in the biomass that are able to efficiently accumulate metals by both extracellular adsorption and intracellular uptake. Biogas production was not affected by the increased metal concentrations. In conclusion, bioaugmentation increased the concentration of metals in dry sludge, which means that it could potentially have negative effects on the environment.

Physiological, biochemical and proteomic insight into integrated strategies of an endophytic bacterium Burkholderia cenocepacia strain YG-3 response to cadmium stress

An endophytic bacterium YG-3 with high cadmium (Cd) resistance was isolated from poplar grown in a composite mine tailing. It was identified as Burkholderia cenocepacia based on genomic, physiological and biochemical analyses. The Cd removal rate by YG-3 could reach about 60.0% in Cd aqueous solution with high concentrations of both 100 and 500 mg L-1. Meanwhile, various absorption and adsorption strategies were found in the two different Cd concentrations. The global resistance mechanisms of YG-3 were investigated in several levels, i.e., physiological observation, such as scanning electron microscopy and transmission electron microscopy; biochemical detection for active compound production and infrared spectroscopy; label-free quantitative proteomic profile analysis. The results indicated that YG-3 possesses a complex mechanism to adapt to Cd stress: (1) binding of Cd to prevent it from entering the cell by the cell wall components, as well as secreted siderophores and exopolysaccharides; (2) intracellular sequestration of Cd by metalloproteins; (3) excretion of Cd from the cell by efflux pumps; (4) alleviation of Cd toxicity by antioxidants. Our results demonstrate that endophyte YG-3 is well adjusted to largely remove Cd and has potential to cooperate with its host to improve phytoremediation efficiency in heavy metal-contaminated sites.

Heavy metal induced stress on wheat: phytotoxicity and microbiological management

Among many soil problems, heavy metal accumulation is one of the major agronomic challenges that has seriously threatened food safety. Due to these problems, soil biologists/agronomists in recent times have also raised concerns over heavy metal pollution, which indeed are unpleasantly affecting agro-ecosystems and crop production. The toxic heavy metals once deposited beyond certain permissible limits, obnoxiously affect the density, composition and physiological activities of microbiota, dynamics and fertility of soil leading eventually to reduction in wheat production and via food chain, human and animal health. Therefore, the metal induced phytotoxicity problems warrant urgent and immediate attention so that the physiological activities of microbes, nutrient pool of soils and concurrently the production of wheat are preserved and maintained in a constantly deteriorating environment. To mitigate the magnitude of metal induced changes, certain microorganisms have been identified, especially those belonging to the plant growth promoting rhizobacteria (PGPR) group endowed with the distinctive property of heavy metal tolerance and exhibiting unique plant growth promoting potentials. When applied, such metal-tolerant PGPR have shown variable positive impact on wheat production, even in soils contaminated with metals, by supplying macro and micro nutrients and secreting active biomolecules like EPS, melanins and metallothionein (MTs). Despite some reports here and there, the phytotoxicity of metals to wheat and how wheat production in metal-stressed soil can be enhanced is poorly explained. Thus, an attempt is made in this review to better understand the mechanistic basis of metal toxicity to wheat, and how such phytotoxicity can be mitigated by incorporating microbiological remediation strategies in wheat cultivation practices. The information provided here is likely to benefit wheat growers and consequently optimize wheat production inexpensively under stressed soils.

Among many soil problems, heavy metal accumulation is one of the major agronomic challenges that has seriously threatened food safety.

Efficient biodegradation of petroleum n-alkanes and polycyclic aromatic hydrocarbons by polyextremophilic Pseudomonas aeruginosa san ai with multidegradative capacity

Pseudomonas aeruginosa san ai degraded individual selected petroleum compounds: n-hexadecane, n-nonadecane, fluorene, phenanthrene, and pyrene with high efficiency, at initial concentrations of 20 mg L⁻¹ and in seven days.

Evaluation of mitochondrial toxicity of cadmium in clam Ruditapes philippinarum using iTRAQ-based proteomics

Cadmium is one of the most serious metal pollutants in the Bohai Sea. Previous studies revealed that mitochondrion might be the target organelle of Cd toxicity. However, there is a lack of a global view on the mitochondrial responses in marine animals to Cd. In this work, the mitochondrial responses were characterized in clams Ruditapes philippinarum treated with two concentrations (5 and 50 μg/L) of Cd for 5 weeks using tetraethylbenzimidazolylcarbocyanine iodide (JC-1) staining, ultrastructural observation and quantitative proteomic analysis. Basically, a significant decrease of mitochondrial membrane potential (△Ψm) was observed in clams treated with the high concentration (50 μg/L) of Cd. Cd treatments also induced specific morphological changes indicated by elongated mitochondria. Furthermore, iTRAQ-based mitochondrial proteomics showed that a total of 97 proteins were significantly altered in response to Cd treatment. These proteins were closely associated with multiple biological processes in mitochondria, including tricarboxylic acid (TCA) cycle, oxidative phosphorylation, fatty acid β-oxidation, stress resistance and apoptosis, and mitochondrial fission. These findings confirmed that mitochondrion was one of the key targets of Cd toxicity. Moreover, dynamical regulations, such as reconstruction of energy homeostasis, induction of stress resistance and apoptosis, and morphological alterations, in mitochondria might play essential roles in Cd tolerance. Overall, this work provided a deep insight into the mitochondrial toxicity of Cd in clams based on a global mitochondrial proteomic analysis.

A comprehensive study of conditions of the biodegradation of a plastic additive 2,6-di-tert-butylphenol and proteomic changes in the degraderPseudomonas aeruginosasan ai

ThePseudomonas aeruginosasan ai strain was investigated for its capability to degrade the 2,6-di-tert-butylphenol (2,6-DTBP) plastic additive, a hazardous and toxic substance for aquatic life.

Multiple siderophores: bug or feature?

It is common for bacteria to produce chemically diverse sets of small Fe-binding molecules called siderophores. Studies of siderophore bioinorganic chemistry have firmly established the role of these molecules in Fe uptake and provided great insight into Fe complexation. However, we still do not fully understand why microbes make so many siderophores. In many cases, the release of small structural variants or siderophore fragments has been ignored, or considered as an inefficiency of siderophore biosynthesis. Yet, in natural settings, microbes live in complex consortia and it has become increasingly clear that the secondary metabolite repertoires of microbes reflect this dynamic environment. Multiple siderophore production may, therefore, provide a window into microbial life in the wild. This minireview focuses on three biochemical routes by which multiple siderophores can be released by the same organism-multiple biosynthetic gene clusters, fragment release, and precursor-directed biosynthesis-and highlights emergent themes related to each. We also emphasize the plurality of reasons for multiple siderophore production, which include enhanced iron uptake via synergistic siderophore use, microbial warfare and cooperation, and non-classical functions such as the use of siderophores to take up metals other than Fe.

A histidine-rich Pseudomonas metallothionein with a disordered tail displays higher binding capacity for cadmium than zinc

The NMR solution structure of a Pseudomonas metallothionein reveals a different binding capacity for Zn^II and Cd^II ions that results in two novel metal-cluster topologies. Replacement of a non-coordinating residue by histidine decreases the kinetic lability of the cluster. All three structures reported show an identical protein fold.