Sensitivity of Various Bacteria, Including Actinomycetes, and Fungi to Cadmium and the Influence of pH on Sensitivity

Microbiological status of natural and anthropogenic soils of the Taganrog Bay coast at different levels of combined pollution with heavy metals and PAHs

The effect of heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) pollution on the microbiological status of soils on the coast of the Taganrog Bay and adjacent areas was studied. The content of total and exchangeable forms of HMs, the content of 16 priority PAHs and the abundance of several groups of culturable microorganisms was determined, namely copiotrophic, prototrophic, aerobic spore-forming bacteria, actinomycetes, molds and yeasts. The content of total and exchangeable forms of HMs in urban coastal soils in industrial zone significantly exceeded that in non-urban soils. The maximum concentrations of total forms of Mn, Cr, Ni, Cu, Zn, Pb and Cd are 1821, 871, 143, 89, 1390, 317 and 10 mg/kg, respectively. The median value of the total content of 16 PAHs in urban soils is 3 times higher than in the soils of natural areas and reached 4309 ng/g. The lowest numbers of copiotrophic bacteria, prototrophic bacteria and aerobic spore-forming bacteria were found in the soils of industrial zone: 6.8, 13.8 and 0.63 million CFU g-1 dry soil, respectively. The largest numbers of copiotrophic bacteria, prototrophic bacteria and aerobic spore-forming bacteria were recorded in the soils of natural areas-72.5, 136 and 5.73 million CFU g-1 dry soil, respectively. It was found that the abundance of copiotrophs, prototrophs, and aerobic spore-forming bacteria is more affected by the urbanization of coastal soils including the pollution of HMs and PAHs. Other groups of microorganisms (actinomycetes, molds and yeasts) turned out to be more resistant to anthropogenic factors.

The emerging potential of natural and synthetic algae-based microbiomes for heavy metal removal and recovery from wastewaters

Heavy Metal (HM) bioremoval by microbes is a successful, environment-friendly technique, particularly at low concentrations of HMs. Studies using algae, bacteria, and fungi reveal promising capabilities in isolation and when used in consortia. Yet, few reviews have emphasized individual and collective HM removal rates and the associated mechanisms in natural or synthetic microbiomes. Besides discussing the limitations of conventional and synthetic biology approaches, this review underscores the utility of indigenous microbial taxon, i.e., algae, fungi, and bacteria, in HM removal with adsorption capacities and their synergistic role in microbiome-led studies. The detoxification mechanisms studied for certain HMs indicate distinctive removal pathways in each taxon which points to an enhanced effect when used as a microbiome. The role and higher efficacies of the designer microbiomes with complementing and mutualistic taxa are also considered, followed by recovery options for a circular bioeconomy. The citation network analysis further validates the multi-metal removal ability of microbiomes and the restricted capabilities of the individual counterparts. In precis, the study reemphasizes increased metal removal efficiencies of inter-taxon microbiomes and the mechanisms for synergistic and improved removal, eventually drawing attention to the benefits of ecological engineering approaches compared to other alternatives.

Cadmium-resistant Chryseobacterium sp. DEMBc1 strain: characteristics and potential to assist phytoremediation and promote plant growth

The effectiveness of phytoremediation is closely related to the various interactions between pollutants, soil particles, rhizosphere microorganisms, and plants. Therefore, the object of current study was a cadmium-tolerant bacterium isolated from the rye rhizosphere, with a high degree of genetic similarity to the genus Chryseobacterium. Chryseobacterium sp. DEMBc1 was able to grow with 36 different BiologGN2 carbon sources and show the adaptation to stress factors such as Cd (100 μg ml^-1), low temperature (8 °C), and salinity (2% NaCl). Furthermore, it was shown that DEMBc1 had the characteristics of plant growth-promoting microorganisms: it was able to produce ammonia, indole acetic acid, 1-aminocyclopropane-1-carboxylic acid deaminase, and siderophores, as well as solubilize Ca₃(PO₄)₃. After inoculation with DEMBc1, a significant decrease in the concentration of Cd was observed in the roots of Festuca ovina grown in Cd-polluted soil, compared to the non-inoculated Cd-polluted soil. It was also noticed that DEMBc1 produced a large amount of extracellular polymeric substances that were significantly higher than the cellular biomass. These polymers can form a barrier to reduce the translocation of Cd from the growth medium to the plant roots. According to the current study, DEMBc1 has a stabilizing potential and can decrease the mobility of Cd in the F. ovina rhizosphere, bioaccumulate metals in plant tissues, and effectively improve the bioavailability of nutrients, especially Fe, N, and P in a polluted environments.

Influence of cadmium-resistant Streptomycetes on plant growth and cadmium uptake by Chlorophytum comosum (Thunb.) Jacques

This work aims to explore the role of cadmium-resistant actinomycetes on promoting plant growth and cadmium uptake in Chlorophytum comosum (Thunb.) Jacques, a spider plant. Actinomycetes isolated from the plant roots in peat swamp forests were screened for their cadmium resistance and the production of indole-3-acetic acid (IAA) and siderophores. The results found that K5PN1 and 11-10SHTh produced high levels of IAA and siderophores, respectively. K5PN1 and 11-10SHTh were identified to be Streptomyces rapamycinicus and Streptomyces cyaneus, respectively. Both strains were able to remove cadmium from aqueous solution and survive under cadmium stress in contaminated soil. The results of pot experiments found that the selected Streptomyces inoculation increased the root and shoot biomass and cadmium accumulation in the root and shoot of C. comosum planted in a cadmium-contaminated soil. The highest cadmium accumulation and translocation ability of cadmium from the root to shoot was found in C. comosum with S. rapamycinicus inoculation. In addition, plant with S. cyaneus inoculation had the highest phytoextraction coefficient and bioaccumulation factor. Our findings concluded that S. rapamycinicus and S. cyaneus stimulated the growth and cadmium uptake in C. comosum, suggesting a combined approach using the selected Streptomyces and C. comosum for phytoremediation of cadmium-polluted soil.

Multimetal bioremediation and biomining by a combination of new aquatic strains of Mucor hiemalis

Here we describe a unique microbial biotechnology for simultaneous bioremediation and biomining of twelve ionic metals overcoming the obstacles of multimetal toxicity to microbes. After a thorough search of key microorganisms in microbiomes of many sulfidic springs in Bavaria (Germany) over an area of 200 km², we found three new strains EH8, EH10 and EH11 of Mucor hiemalis physiologically compatible and capable of multimetal-remediation and enrichment. We combined the multimetal-resistance, hyper-accumulation and elicitation power of EH8, EH10 and EH11 to develop a novel biotechnology for simultaneous removal, fractionation and enrichment of metal ions. As a first step we showed the intracellular fixing and deposition of mercury as nanospheres in EH8's sporangiospores. Scanning Electron Microscopy-Energy-Dispersive X-Ray analysis revealed binding and precipitation of other applied metal ions as spherical nano-particles (~50-100 nm) at the outer electro-negative cellwall-surface of EH8, EH10 and EH11 sporangiospores. Microbiomes, germinated spores and dead insoluble cellwalls of these strains removed >81-99% of applied Al, Cd, Co, Cr, Cu, Hg, Ni, Pb, U, and Zn simultaneously and furthermore enriched precious Ag, Au and Ti from water all within 48 h, demonstrating the potential of new biotechnologies for safe-guarding our environment from metal pollution and concentrating precious diluted, ionic metals.

Dibutyl phthalate contamination remolded the fungal community in agro-environmental system

Dibutyl phthalate (DBP) is a typical soil contaminant that is widely used as plasticizer in modern agricultural production. In this study, an experiment was conducted to evaluate fungal community succession in a soil-vegetable ecosystem under different DBP concentrations. By using high-throughput sequencing of the ribosomal internal transcribed spacer (ITS) region, it was shown that DBP contamination caused significant changes to the soil fungal community, in terms of both α and β diversities. The largest changes in fungal α and β diversities were detected under 50 mg/kg DBP concentration at the first day of addition. The bulk soils, rhizosphere soils and the phyllosphere harbored different fungal communities, while the abundance of saprotrophs and plant pathogens in the phyllosphere have been increased under DBP contamination. From correlation analysis and partial Mantel test, the change in fungal community α diversity was the result of multiple factors (DBP concentration, bacterial community and soil properties) while the β diversity of fungal community was mainly co-varied with the bacterial community after DBP contamination. Moreover, molecular ecological network analysis demonstrated that DBP contamination was detrimental to mutualistic relationships among fungal species and destabilized the network structure. Overall, the fungal communities in soils and around vegetables were largely remolded by DBP contamination that provides new insight into DBP contamination impacts on agricultural ecosystems.

Evaluation of plant growth promoting activity and heavy metal tolerance of psychrotrophic bacteria associated with maca (Lepidium meyenii Walp.) rhizosphere

The high Andean plateau of Peru is known to suffer harsh environmental conditions. Acidic soils containing high amount of heavy metals due to mining activities and withstanding very low temperatures affect agricultural activities by diminishing crop quality and yield. In this context, plant growth promoting rhizobacteria (PGPR) adapted to low temperatures and tolerant to heavy metals can be considered as an environment-friendly biological alternative for andean crop management. The aim of this work was to select and characterize psychrotrophic PGPR isolated from the rhizosphere of maca (Lepidium meyenii Walp.) a traditional andean food crop. A total of 44 psychrotrophic strains isolated from 3 areas located in the Bombon plateu of Junin-Peru were tested for their PGPR characteristics like indole acetic acid (IAA) production, phosphate solubilization and for their ability to improve seed germination. In addition, their capacity to grow in the presence of heavy metals like cadmium (Cd), lead (Pb), cobalt (Co) and mercury (Hg) was tested. Of the total number of strains tested, 12 were positive for IAA production at 22 °C, 8 at 12 °C and 16 at 6 °C. Phosphate solubilization activities were higher at 12 °C and 6 °C than at 22 °C. Red clover plant assays showed that 16 strains were capable to improve seed germination at 22 °C and 4 at 12 °C. Moreover, 11 strains showed tolerance to Cd and Pb at varying concentrations. This study highlight the importance of obtaining PGPRs to be used in high andean plateu crops that are exposed to low temperatures and presence of heavy metals on soil.

Effects of cadmium-resistant fungi Aspergillus aculeatus on metabolic profiles of bermudagrass [Cynodondactylon (L.)Pers.] under Cd stress

Plants' tolerance to heavy metal stress may be induced by the exploitation of microbes. The objectives of this study were to investigate the effect of cadmium (Cd)-resistant fungus, Aspergillus aculeatus, on tolerance to Cd and alteration of metabolites in bermudagrass under Cd stress, and identify the predominant metabolites associated with Cd tolerance. Two genotypes of bermudagrass with contrasting Cd tolerance (Cd-sensitive 'WB92' and Cd-tolerant 'WB242') were exposed to 0, 50, 150 and 250 mg kg^-1 Cd for 21 days. Physiological responses of bermudagrass to Cd stress were evaluated based on the relative growth rate (RGR) and normalized relative transpiration rate (NRT). Plants inoculated with A. aculeatus exhibited higher RGR and NRT under Cd stress than those of non-inoculated plants, regardless of genotypes. A total of 32 Cd-responsive metabolites in leaves and 21 in roots were identified in the two genotypes, including organic acids, amino acids, sugars, and fatty acids and others. Interestingly, under Cd stress, the leaves of inoculated 'WB92' accumulated less citric acid, aspartic acid, glutamic acid, sucrose, galactose, but more sorbose and glucose, while inoculated 'WB242' leaves had less citric acid, malic acid, sucrose, sorbose, but more fructose and glucose, compared to non-inoculated plants. In 'WB92' roots, the A. aculeatus reduced mannose content, but increased trehalose and citric acid content, while in 'WB242', it decreased sucrose, but enhanced citric acid content, compared to Cd regime. The results of this study suggest that A. aculeatus may induce accumulation of different metabolites associated with Cd tolerance in bermudagrass.

Bioavailability of heavy metals in soil: impact on microbial biodegradation of organic compounds and possible improvement strategies

Co-contamination of the environment with toxic chlorinated organic and heavy metal pollutants is one of the major problems facing industrialized nations today. Heavy metals may inhibit biodegradation of chlorinated organics by interacting with enzymes directly involved in biodegradation or those involved in general metabolism. Predictions of metal toxicity effects on organic pollutant biodegradation in co-contaminated soil and water environments is difficult since heavy metals may be present in a variety of chemical and physical forms. Recent advances in bioremediation of co-contaminated environments have focussed on the use of metal-resistant bacteria (cell and gene bioaugmentation), treatment amendments, clay minerals and chelating agents to reduce bioavailable heavy metal concentrations. Phytoremediation has also shown promise as an emerging alternative clean-up technology for co-contaminated environments. However, despite various investigations, in both aerobic and anaerobic systems, demonstrating that metal toxicity hampers the biodegradation of the organic component, a paucity of information exists in this area of research. Therefore, in this review, we discuss the problems associated with the degradation of chlorinated organics in co-contaminated environments, owing to metal toxicity and shed light on possible improvement strategies for effective bioremediation of sites co-contaminated with chlorinated organic compounds and heavy metals.

Heavy metal toxicity to bacteria - are the existing growth media accurate enough to determine heavy metal toxicity?

A new minimal medium was formulated considering the limitations of the existing media for testing heavy metal sensitivity to bacteria. Toxicity of cadmium and copper to three bacteria was investigated in the new medium and compared with three other media commonly used to study the effect of the toxic metals. Based on speciation data arrived at using ion-selective electrodes, the available free-metal concentration in solution was highest in the MES-buffered medium. This finding was strongly supported by the estimated EC(50) values for the metals tested based on the toxicity bioassays. The free-ionic cadmium and copper concentrations in the medium provide more accurate determination of metal concentrations that affects the bacteria, than with most of other existing media. This will avoid doubts on other media and misleading conclusions relevant to the toxicity of heavy metals to bacteria and provides a better option for the study of metal-bacteria interactions.

Effects of selected soil properties on phytoremediation applicability for heavy-metal-contaminated soils in the Apulia region, Southern Italy

Phytoremediation is a well-known promising alternative to conventional approaches used for the remediation of diffused and moderated contaminated soils. The evaluation of the accumulation, availability, and interactions of heavy metals in soil is a priority objective for the possible use of phytoremediation techniques such as phytoextraction and phytostabilization. The soils used in this work were collected from a number of sites inside a protected area in the Apulia region (Southern Italy), which were contaminated by various heavy metals originated from the disposal of wastes of different sources of origin. Soils examined contained Cd, Cr, Cu, Ni, Pb, and Zn in amounts exceeding the critical limits imposed by EU and Italian laws. However, the alkaline conditions, high organic matter content, and silty to silty loamy texture of soils examined would suggest a reduced availability of heavy metals to plants. Due to the high total content but the low available fraction of heavy metals analyzed, especially Cr, phytoextraction appears not to be a promising remediation approach in the sites examined, whereas phytostabilization appears to be the best technique for metal decontamination in the studied areas.

Indigenous soil bacteria with the combined potential for hydrocarbon consumption and heavy metal resistance

INTRODUCTION

Transconjugant bacteria with combined potential for hydrocarbon utilization and heavy metal resistance were suggested by earlier investigators for bioremediation of soils co-contaminated with hydrocarbons and heavy metals. The purpose of this study was to offer evidence that such microorganisms are already part of the indigenous soil microflora.

METHODS

Microorganisms in pristine and oily soils were counted on nutrient agar and a mineral medium with oil as a sole carbon source, in the absence and presence of either sodium arsenate (As V), sodium arsenite (As III) or cadmium sulfate, and characterized via 16S rRNA gene sequencing. The hydrocarbon-consumption potential of individual strains in the presence and absence of heavy metal salts was measured.

RESULTS

Pristine and oil-contaminated soil samples harbored indigenous bacteria with the combined potential for hydrocarbon utilization and As and Cd resistance in numbers up to 4 × 10⁵ CFU g⁻¹. Unicellular bacteria were affiliated to the following species arranged in decreasing order of predominance: Bacillus subtilis, Corynebacterium pseudotuberculosis, Brevibacterium linens, Alcaligenes faecalis, Enterobacter aerogenes, and Chromobacterium orangum. Filamentous forms were affiliated to Nocardia corallina, Streptomyces flavovirens, Micromonospora chalcea, and Nocardia paraffinea. All these isolates could grow on a wide range of pure aliphatic and aromatic hydrocarbons, as sole sources of carbon and energy, and could consume oil and pure hydrocarbons in batch cultures. Low As concentrations, and to a lesser extent Cd concentrations, enhanced the hydrocarbon-consumption potential by the individual isolates.

CONCLUSION

There is no need for molecularly designing microorganisms with the combined potential for hydrocarbon utilization and heavy metal resistance, because they are already a part of the indigenous soil microflora.

Comparing the tolerance limits of selected bacterial and protozoan species to nickel in wastewater systems

Heavy-metal resistant microorganisms play a significant role in the treatment of industrial wastewater. The detoxifying ability of these resistant microorganisms can be manipulated for bioremediation of heavy metals in wastewater systems. This study aimed at comparing the tolerance limit of selected wastewater protozoan species (Aspidisca sp., Trachelophyllum sp. and Peranema sp.) against Ni(2+) with that of selected bacterial species (Bacillus licheniformis-ATCC12759, Brevibacillus laterosporus-ATCC64 and Pseudomonas putida-ATCC31483) commonly found in wastewater systems. The isolates were exposed to various concentrations of Ni(2+) in mixed liquor and their tolerance to Ni(2+) assessed at different temperatures (25°C, 30°C, 35°C and 40°C) and pHs (4, 6, 7, 8 and 10). The physicochemical parameters such as chemical oxygen demand (COD) and dissolved oxygen (DO) of the media and the growth rates of the isolates were measured using standard methods. In terms of their minimum inhibitory concentrations (MIC), the results revealed that the isolates could tolerate Ni(2+) at concentrations ranging between 32 and 52ppm for protozoa and between 52 and 84ppm for bacteria. B. licheniformis-ATCC12759 was the most tolerant bacterial species (MIC: 84ppm-Ni(2+)) while Peranema sp. was the most tolerant protozoan species (MIC: 52ppm-Ni(2+)). At 10 and/or 20ppm-Ni(2+) the growth of B. licheniformis-ATCC12759 (6.30 days(-1) for 10 and 5.73 days(-1) for 20ppm-Ni(2+)), P. putida-ATCC31483 (6.02 days(-1) for 10 and 5.31 days(-1) for 20ppm-Ni(2+)) and Peranema sp. (2.15 days(-1) for 10ppm-Ni(2+)) was stimulated after one day of incubation. Statistical evidence showed significant differences (p=0.0065) between the MIC of the six isolates and positive correlations between COD and the growth rates of isolates (r=0.8999/0.8810 for bacteria/protozoa). The tolerance limit of all isolates was significantly dependent on the pH and the temperature. The study suggests that these isolates can be used for the bioremediation of nickel in industrial wastewater systems.

Influence of pH and inorganic phosphate on toxicity of zinc to Arthrobacter sp. isolated from heavy-metal-contaminated sediments

Because of its high solubility over a wide range of pH conditions, zinc is found in many natural and human-impacted systems. Zinc speciation is critical in assessing zinc toxicity to microorganisms because it varies considerably with pH and is dependent on other aqueous constituents. Combined results of thermodynamic modeling, statistical analysis, and batch culture studies using Arthrobacter sp. JM018 suggest that the toxic species may not be solely limited to the free ion, but also includes ZnHPO(4)(0)(aq). Cellular uptake of ZnHPO(4)(0)(aq) through the inorganic phosphate transporter (Pit family), which requires a neutral metal phosphate complex for phosphate transport, may explain the observed toxicity. Based on visual MINTEQ (v3.0) modeling, at 50 μM total zinc, ZnHPO(4)(0)(aq) constitutes 33, 70, and 76% of the neutral metal phosphate pool at pH 6, 7, and 8, respectively. At 50 μM total zinc, cultures supplied with organic phosphate (glycerol-3-phosphate) show no significant response to pH (p = 0.13) while inhibition of inorganic phosphate-supplemented cultures, whose neutral metal phosphates are increasingly dominated by ZnHPO(4)(0)(aq), show significant pH dependence (p = 9.45 × 10(-7)). Using sodium to decrease the distribution of ZnHPO(4)(0)(aq) in the neutral metal phosphate pool also decreased the pH dependent toxicity, further supporting this mechanism. These findings show the important role of minor zinc species in organism toxicity and have wider implications because the Pit inorganic phosphate transport system is widely distributed in Bacteria, Archaea, and Eukarya.

Effects of Glucose Concentrations on Cadmium, Copper, Mercury, and Zinc Toxicity to a Klebsiella sp

The influence of glucose concentration on Cd, Cu, Hg, and Zn toxicity to a Klebsiella sp. was studied by following the degradation of C-labeled glucose at pH 6.0. Uptake of C into the cells was also determined. The carbon concentrations ranged from 0.01 to 40 mg liter, which are equivalent to soluble C concentrations in natural environments. The toxicity of Cu, Cd, and Zn to a Klebsiella sp. was affected considerably by the C concentration. Copper at 10 M was toxic when the carbon concentration was 10 or 40 mg liter, while at 0.01 to 1.0 mg liter no toxicity was observed. Cadmium and zinc were toxic at 10 M in media containing 0.01 to 1.0 mg of C liter. At C concentrations greater than 1.0 mg liter, the inhibition of glucose degradation and carbon assimilation was observed at 10 M Cd and Zn. The toxicity of mercury seemed to be independent of the C concentration. Results of this study showed that the nutritional state of an organism may have a profound effect on its sensitivity to metals. Metals taken up by an energy-driven transport system may be less toxic under conditions of C starvation. The C concentration should be taken into account when evaluating results from toxicity studies, especially as most microorganisms in nature live under energy-limited conditions.

Effect of metal-rich sewage sludge application on the bacterial communities of grasslands

The effect of long-term application of heavy metal-laden sewage sludge on the total heterotrophic aerobic and the cadmium-resistant soil bacterial communities was studied. Gram-positive bacteria were completely absent from resistant communities. These findings suggest that this group is highly susceptible to Cd. Shannon's diversity indices estimated for total communities did not reveal negative effects on the communities that developed in the presence of sludge. However, Cd-resistant communities isolated from long-term sludge-amended soils were more diverse than the resistant communities from a control sample, suggesting that adaptation to Cd as a stressor had occurred in the presence of sludge constituents. This higher diversity was attributed to Cd resistance in pseudomonads and gram-negative fermenters. Resistance did not develop by dissemination of Cd resistance plasmids, because these were rarely detected in the genomes of resistant strains.

The influence of cadmium on life-history parameters and gut microflora of Archegozetes longisetosus (Acari: Oribatida) under laboratory conditions

We tested the effect of cadmium (25, 130 microg Cd g(-1)), administered via Chinese cabbage (Brassica chinensis L.) as food on life-history parameters and gut microflora of tritonymphs and adults of the oribatid mite, Archegozetes longisetosus Aoki. Both concentrations of Cd had an adverse effect on offspring mortality, and the higher concentration also reduced female fecundity, as well as the number of bacteria, fungi and actinomycetes, and it changed the community structure of bacteria; the proportion of gram-negative bacteria increased while that of gram-positive bacteria declined. Interestingly, at the lower Cd concentration microflora was more abundant and diverse than in the control group, especially in the tritonymphs, although the mean activity of gut microflora was reduced. The higher Cd concentration reduced microflora activity both in the tritonymphs and adults.

Single and combined effects of nickel (Ni(II)) and cobalt (Co(II)) ions on activated sludge and on other aerobic microorganisms: a review

Nickel (N(II)) and cobalt (Co(II)) are often encountered in wastewaters. As conventional wastewater treatment may only partially remove nickel and cobalt, a large fraction of the above metals is released to the aquatic environment. Both metals have been identified as micronutrients, at trace concentrations; however, they are both microbial growth inhibitors, at relatively high concentrations. On the other hand, the combined effects (e.g.: growth stimulation or toxicity) of the above metals have been found to differ from the summation of the effects which occur when the metals are applied individually. Moreover, a number of environmental factors (e.g.: pH, biomedium composition, biomass concentration, presence of other heavy metals) can affect the microbial toxicity of the above metallic species. The present review discusses, in a systematic way, the individual and joint effects of the above heavy metals to the growth of microorganisms grown under aerobic conditions, with focus on the growth of activated sludge. Data on multi-metal toxicity are particularly useful in establishing criteria for heavy metal tolerance levels in the environment.

Heavy metal resistant of E. coli isolated from wastewater sites in Assiut City, Egypt

Twelve isolates of E. coli were isolated from wastewater of El-Malah canal located in Assiut, Egypt and were checked for their heavy metal tolerance. One isolate has tested for its multiple metal resistances and found to be plasmid mediated with molecular weights 27 and 65 kb for hexa- and trivalent chromium. It was identified as E. coli ASU 7. Its minimal inhibitory concentration (MIC) for Cu(2+), Co(2+), Ni(2+), Zn(2+), Cr(6+), Cr(3+), Cd(2+) and Pb(2+) were 1.57, 2.55, 1.7, 9.17, 0.48, 7.69, 4.4 and 3.1 mM, respectively. Growth kinetics was determined under Cr(6+) and Cr(3+) stress. SDS-PAGE of protein profile shows that 10 ppm (0.19 mM) of Cr(6+) induces new protein with molecular weight 23 kDa.

Identification of dominant bacterial phylotypes in a cadmium-treated forest soil

The presence of heavy metals in soils can lead to changes in microbial community structure, characterized by the dominance of groups that are able to tolerate contamination. Such groups may provide good microbial indicators of heavy-metal pollution in soil. Through terminal restriction fragment length polymorphism (T-RFLP) profiling, changes in the bacterial community structure of an acidic forest soil that had been incubated with cadmium (Cd) for 30 days were investigated. T-RFLP revealed, in particular, three operational taxonomic units (OTUs) strongly dominating in relative abundance in the contaminated soil. By cloning of the amplified 16S rRNA genes and partial sequencing of 25 clones, these three dominant OTUs were phylogenetically characterized. One dominant OTU in the cadmium-contaminated soil was derived from Betaproteobacteria, genus Burkholderia, and the other two were from uncultured members of the class Actinobacteria, closely related to the genus Streptomyces. To confirm T-RFLP data, four primers were designed on the basis of this study's dominant sequences, targeting the OTUs corresponding to Burkholderia or Actinobacteria. Real-time PCR showed that Burkholderia target sequences were more abundant in cadmium-treated soil (7.8 x 10(7)+/- 3.0 x 10(7) targets g(-1) soil) than in untreated soil (4.0 x 10(6)+/- 8.9 x 10(5) targets g(-1) soil). It was concluded that the genus Burkholderia includes species that may be particularly dominant under cadmium contamination.

Responses in the mycelial growth of Aspergillus niger isolates to arsenic contaminated environments and their resistance to exogenic metal stress

Isolates of Aspergillus niger, selected from coal dust sediment of a mine containing As (400 mg/kg), pH 3.3-2.8, and from river sediment found near the mine (As, 363 mg/kg, Sb, 93 mg/kg), pH 5.2-4.8, growing on Czapek-Dox agar exhibited distinct responses in the mycelial growth in arsenic contaminated environments. The radial growth of the isolate from the coal dust in comparison to the control strain from an environment without pollution was reduced approximately to one-half. It formed black, very small compact colonies, with dense sporulation. The opposite, the strain from the river sediment, grew better in Czapek-Dox agar like the control. It formed larger colonies with dense centre and strong sporulation. Also, the culture from river sediment developed faster than the coal dust isolate and control strain. Differences were also recorded in size and thickness of conidia heads, phialide, metulae, and conidiophores. Both isolates from contaminated localities exhibited higher tolerance to exogenic toxic effects of As5+, Cd2+ and Cu2+ (5, 25 or 50 mg/l) than the control culture. Tolerance was monitored using the growth of biomass in liquid Czapek-Dox medium. We confirmed the morphological identification of our isolates to A. niger species with the PCR method. The results refer to complicated relations between biotic and abiotic effects that may directly affect the processes observed in the in situ environment.

Influence of pH on copper and zinc sensitivity of ericoid mycobionts in vitro

The effect of pH on growth, metal uptake and toxicity in four isolates of ericoid mycobionts (two Hymenoscyphus ericae from unpolluted heathland sites and two H. ericae-type mycobionts from metal-contaminated mine spoil) was assessed in vitro. These isolates were incubated in liquid medium (10% Rorison's medium, glucose at 10 g l(-1)) containing either 0.25 mM Cu or 2.0 mM Zn and adjusted to pH 2, 3, 4, 5 or 6. After 30 days incubation, dry mass and mycelial metal content were determined and growth was expressed as tolerance index, i.e. dry mass in the presence of metal as a percentage of dry mass in the absence of metal. Initial medium pH had a significant effect on both tolerance index and metal accumulation. Tolerance indices were highest at pH 2, with several isolates showing a stimulation of growth (i.e. tolerance index >100%) at this pH. Tolerance index decreased at higher initial pH values and growth of two mycobionts was completely inhibited (tolerance index=0) in the Cu-supplemented media at pH 6. Reduction in tolerance index coincided with an increase in mycelial accumulation of Cu and Zn. Practical and environmental implications of these results are discussed.

Heavy-metal stress and developmental patterns of arbuscular mycorrhizal fungi

The rate of global deposition of Cd, Pb, and Zn has decreased over the past few decades, but heavy metals already in the soil may be mobilized by local and global changes in soil conditions and exert toxic effects on soil microorganisms. We examined in vitro effects of Cd, Pb, and Zn on critical life stages in metal-sensitive ecotypes of arbuscular mycorrhizal (AM) fungi, including spore germination, presymbiotic hyphal extension, presymbiotic sporulation, symbiotic extraradical mycelium expansion, and symbiotic sporulation. Despite long-term culturing under the same low-metal conditions, two species, Glomus etunicatum and Glomus intraradices, had different levels of sensitivity to metal stress. G. etunicatum was more sensitive to all three metals than was G. intraradices. A unique response of increased presymbiotic hyphal extension occurred in G. intraradices exposed to Cd and Pb. Presymbiotic hyphae of G. intraradices formed presymbiotic spores, whose initiation was more affected by heavy metals than was presymbiotic hyphal extension. In G. intraradices grown in compartmentalized habitats with only a portion of the extraradical mycelium exposed to metal stress, inhibitory effects of elevated metal concentrations on symbiotic mycelial expansion and symbiotic sporulation were limited to the metal-enriched compartment. Symbiotic sporulation was more sensitive to metal exposure than symbiotic mycelium expansion. Patterns exhibited by G. intraradices spore germination, presymbiotic hyphal extension, symbiotic extraradical mycelium expansion, and sporulation under elevated metal concentrations suggest that AM fungi may be able to survive in heavy metal-contaminated environments by using a metal avoidance strategy.

Mechanisms of cadmium resistance in anaerobic bacterial enrichments degrading pentachlorophenol

The mechanisms of heavy-metal resistance used by adapted sulfidogenic and methanogenic enrichments degrading pentachlorophenol in the presence of cadmium (Cd) were studied. The enrichment cultures adapted to and readily tolerated bioavailable Cd concentrations up to 50 ppm while degrading an equal concentration of pentachlorophenol. Both cultures removed >95% of the Cd from solution. Transmission electron micrographs revealed (i). the presence of electron-dense particles surrounding the cells in the sulfidogenic enrichments and (ii). the unusual clumping of cells and the presence of an exopolymer in the methanogenic enrichments. Energy dispersive X-ray analysis showed that the sulfidogenic enrichments removed Cd by extracellular precipitation of cadmium sulfide, while the methanogenic enrichment culture removed Cd by extracellular sequestration of Cd into the exopolymer.

Heavy metal pollution in the soils of various land use types based on physicochemical characteristics

In this study, soil samples were collected at eight different regional types of Seoul City and analyzed for their physicochemical properties. In addition, the distribution of heavy metal concentrations was analyzed using samples representing both the surface and deep soil layer. The physicochemical properties analyzed for those samples included parameters such as pH, moisture content, apparent (and true) density, pore ratio, solid content, conductivity, ionic strength, total dissolved solid (TDS), total organic carbon (TOC), and total phosphorus (TP). The contents of heavy metal components contained in plant leaves were also analyzed and compared with those measured from different soil layers. Contents of Cu and Cd were highest in the DH area among eight locations investigated and Pb was higher in the surface soil samples of the GS region than any other locations. According to physicochemical properties of the surface and deep soils, acidity was higher in the surface than deep soils. Depending on the selection of treatment method between strong and weak acids, the metal concentrations were larger by 3-5 times in the strong acid than the weak acid treatments. In addition, metals were higher in the deep than in the surface soil and relative metal contents of leaf samples closely resembled those of soil samples. Results of this study suggest that the physicochemical properties of soils determined from different regional types of Seoul area exhibited a close relationship with the land use types and environmental conditions surrounding each region.

The impact of surface attachment on cadmium accumulation by Pseudomonas fluorescens H2

Cadmium accumulation by Pseudomonas fluorescens H2 attached to glass surfaces and by cells free in suspension in maleate buffer was compared and showed several major differences. The time to saturation of cells with Cd(2+) was different for attached and free cells, although both showed biphasic uptake of Cd(2+). The accumulation of Cd(2+) by free cells was inhibited by the presence of zinc but remained several orders of magnitude higher than accumulation by attached cells. The presence of Zn(2+), however, did not inhibit Cd(2+) uptake by cells attached to the solid substratum. Cadmium uptake still increased with Cd(2+) concentration for both free and attached cells in the presence of Zn(2+). The accumulation of Cd(2+) by both free and attached cells increased with pH up to pH 11. The presence of a metabolic inhibitor, carbomyl cyanide m-chlorophenyl-hydrazone, reduced the uptake of Cd(2+) by free cells by 40% but reduced uptake by attached cells by only 25%. Approximately 65% of Cd(2+) accumulated by cells free in suspension was associated with the cell wall, 33% was present in the cytoplasm and only 2% was bound to exopolymer. The results suggest that the characteristics of heavy metal accumulation by bacterial cells are substantially affected by attachment to solid surfaces.

Chromium-resistant soil actinomycetes: their tolerance to other metals and antibiotics

Chromium occurs widely in most soils, but generally in trace amounts. Actinomycetes, one of the important components of the microbial population in soils interact with a variety of metals including chromium. This study was aimed to evaluate the tolerance of soil actinomycetes to Cr6+, other metals and antibiotics. Thirty-two actinomycete isolates were screened for their tolerance to Cr6+ on tryptone yeast extract agar medium supplemented with Cr6+ at concentrations ranging from 100 to 2000 micrograms ml-1. Thirteen Cr-tolerant isolates were selected on the basis of their growth at the highest concentration, but their performance was not satisfactory in Cr6+ containing liquid salts medium. Resistance of these isolates to other metals and antibiotics was assessed using agar-cup assay and disc diffusion technique, respectively. The sequence of metal toxicity for the actinomycete isolates was in the order Hg2+ > Ni2+ > Cu2+ > Co2+ > Cd2+, but the Cr6+ resistance of the isolates could not be correlated with their antibiotic-resistance profile.

Cadmium removal by a new strain of Pseudomonas aeruginosa in aerobic culture

A fluorescent pseudomonad (strain CW-96-1) isolated from a deep-sea vent sample grew at 30 degrees C under aerobic conditions in an artificial seawater medium and tolerated cadmium concentrations up to 5 mM. After 140 h, strain CW-96-1 removed > 99% of the cadmium from solution. Energy dispersive microanalysis revealed that the cadmium was removed by precipitation on the cell wall; sulfide production was confirmed by growth on Kligler's agar. Based on 16S ribosomal DNA sequencing and fatty acid analysis, the microorganism is closely related to Pseudomonas aeruginosa.

Metal biosorption-flotation. Application to cadmium removal

Biosorption using suspended non-living biomass, and flotation (for consequent solid/liquid separation of the metal-loaded biomass) have been studied in the laboratory as a possible combined process, for the removal of toxic metals (i.e., cadmium) from dilute aqueous solutions. The various parameters of the process were investigated in depth, including re-use of biosorbent. A filter aid (contained in the biomass industrial waste used) was found not really to interfere. Zeta-potential measurements of the aforementioned system were also carried out. Promising results were obtained during continuous-flow experiments. A flotation residence time of 4 min was achieved. Metal removal and suspended biomass recovery were generally over 95%.

Microbial biosorption of copper and lead from aqueous systems

Biosorption of metal ions from aqueous systems was evaluated using a culture of acidic soil isolates grown in a completely mixed, aerobic, semi-batch culture reactor. The laboratory scale system was used to test single and bimetallic solutions of copper and lead with sulfates, chlorides, or nitrates. To elucidate the key factors influencing biosorption and to characterize metal uptake by cellular and extra cellular components of the microbial system, a dialysis testing procedure was developed. A direct contact technique was used to determine the rate of metal sorption on cellular surfaces. The effectiveness of biosorption was influenced by pH, initial metal concentrations, and anionic composition. Respirometric tests were carried out to identify potential inhibitory effects of metal accumulation on microbial oxygen uptake rates.

Energetic basis of cadmium toxicity in Staphylococcus aureus

In washed cells of cadmium-sensitive Staphylococcus aureus 17810S oxidizing glutamate, initial Cd2+ influx via the Mn2+ porter down membrane potential (delta psi) was fast due to involvement of energy generated by two proton pumps--the respiratory chain and the ATP synthetase complex working in the hydrolytic direction. Such an unusual energy drain for rapid initial Cd2+ influx is suggested to be due to a series of toxic events elicited by Cd2+ accumulation down delta psi generated via the redox proton pump: (i) strong inhibition of glutamate oxidation accompanied by a decrease of electrochemical proton gradient (delta mu H+) formation via the respiratory chain, (ii) automatic reversal of ATP synthetase from biosynthetic to hydrolytic mode, which was monitored by a decrease of delta mu (H+)-dependent ATP synthesis, (iii) acceleration of the initial Cd2+ influx down delta psi generated by the reversed ATP synthetase, the alternative proton pump hydrolyzing endogenous ATP. The primary, cadmium-sensitive targets in strain 17810S seem to be dithiols located in the cytoplasmic glutamate oxidizing system, prior to the membrane-embedded NADH oxidation system. Inhibition by Cd2+ of delta mu (H+)-dependent ATP synthesis and of pH gradient (delta pH)-linked [14C]glutamate transport is a secondary effect due to cadmium-mediated inhibition of delta mu H+ generation at the cytoplasmic level. In washed cells of cadmium-resistant S. aureus 17810R oxidizing glutamate, Cd2+ accumulation was prevented due to activity of the plasmid-coded Cd2+ efflux system. Consequently, delta mu (H+)-producing and -requiring processes were not affected by Cd2+.

Impact of heavy metals on mass and energy flux within the decomposition process in deciduous forests

: Laboratory experiments on microbial decomposition and on the contribution of diplopods to organic matter decomposition in soil were combined with field studies to reveal the major points of heavy metal effects on the leaf litter decomposition process. The study focused on the accumulation of organic litter material in heavy metal-contaminated soils. Microbial decomposition of freshly fallen leaves remained quantitatively unaffected by artificial lead contamination (1000 mg kg(-1)). The same was true for further decomposed leaf litter material, provided that the breakdown of this material was not influenced by faunal components. Although nutrient absorption in diplopods is affected by high lead contents in the food, this effect alone, however, was shown not to be sufficient for the massive deceleration of the decomposition process under heavy metal influence which could not only be observed in the field but occurred in microcosm studies as well. Reduced reproduction and lower activity of the diplopods most likely were responsible for the observation that lead-influenced diplopods enhanced microbial activity in soil only in a lesser degree than uncontaminated animals did. This effect is assigned to represent the main reason for decreased decomposition rates and the subsequent accumulation of organic material in heavy metal-contaminated soils.

Phospholipid Fatty Acid Composition, Biomass, and Activity of Microbial Communities from Two Soil Types Experimentally Exposed to Different Heavy Metals

The phospholipid fatty acid (PLFA) pattern was analyzed in a forest humus and in an arable soil experimentally polluted with Cd, Cu, Ni, Pb, or Zn at different concentrations. In both soil types, there were gradual changes in the PLFA patterns for the different levels of metal contamination. The changes in the forest soil were similar irrespective of which metal was used, while in the arable soil the changes due to Cu contamination differed from those due to the other metals. Several PLFAs reacted similarly to the metal amendments in the two soil types, while others showed different responses. In both soils, the metal pollution resulted in a decrease in the iso-branched PLFAs i15:0 and i17:0 and in the monounsaturated 16:1ω5 and 16:1ω7 c fatty acids, while increases were found for i16:0, the branched br17:0 and br18:0, and the cyclopropane cy17:0 fatty acids. In the forest soil, the methyl branched PLFAs 10Me16:0, 10Me17:0, and 10Me18:0 increased in metal-polluted soils, indicating an increase in actinomycetes, while in the arable soil a decrease was found for 10Me16:0 and 10Me18:0 in response to most metals. The bacterial PLFAs 15:0 and 17:0 increased in all metal-contaminated samples in the arable soil, while they were unaffected in the forest soil. Fatty acid 18:2ω6, which is considered to be predominantly of fungal origin, increased in the arable soil, except in the Cu-amended samples, in which it decreased instead. Effects on the PLFA patterns were found at levels of metal contamination similar to or lower than those at which effects on ATP content, soil respiration, or total amount of PLFAs had occurred.

Effect of heavy metals on marine Bacillus sp. and Flavobacterium sp

: Responses to varying concentrations of Hg, Cd, and Zn were studied in two strains of bacterial isolates (Flavobacterium sp. and Bacillus sp.) from Indian coastal waters. Growth responses showed inhibition (in terms of percentage reduction with respect to control) and the order of inhibition was Hg>Zn>Cd in the case of Bacillus sp. and Hg>Cd>Zn in the case of Flavobacterium sp. With prolonged incubation Bacillus sp. overcame the inhibitory effect whereas Flavobacterium sp. did not. Higher concentrations of glucose in the growth medium increased the inhibitory effect of the metal. At lower concentrations (15μg ml(-1)) there was a stimulatory effect on [(14)C] glucose uptake on Flavobacterium sp. Our studies showed that the Gram positive isolate was less adaptable to metals than the Gram negative.

Seasonal ecology of hydrocarbon-utilizing microbes in the surface Waters of a river

Seasonal changes in the microbial communities of the New Calabar Riverwater have been investigated. Analyses of the BOD, pH, salinity, oil and grease levels of effluents of industries sited along the river were also conducted. High hydrocarbon-utilizing microbial populations were found. The percentage of hydrocarbon-utilizing heterotrophic bacteria ranged between 0-98% and 0-68% in the rainy and dry months, respectively. Counts of hydrocarbon-utilizing actinomycetes in the rainy months ranged between 0-95% and 2-55% in the dry months. The hydrocarbon-utilizing yeast population ranged between 1-95% and 2-85% for the rainy and dry months, respectively. Rainy month values for hydrocarbon-utilizing mould population ranged from 0-17% while dry month values ranged from 0-47%. The hydrocarbon-utilizing cyanobacterial population ranged between 0-95% and 0-33% in the rainy and dry months, respectively. Our results suggest that the heterotrophic bacterial and cyanobacterial populations are higher in the rainy months than in the dry months. However, the hydrocarbon-utilizing yeast, mould and actinomycete populations did not show seasonal variation.