Effect of Zn-tolerant bacterial strains on growth and Zn accumulation in Orychophragmus violaceus

Several Zn-tolerant bacterial strains were isolated from heavy-metal contaminated sludge, and their effects on root elongation, mobility, and accumulation of Zn in Orychophragmus violaceus were studied. The isolated strains included Bacillus subtilis, B. cereus, Flavobacterium sp. and Pseudomonas aeruginosa which were capable of stimulating root elongation in O. violaceus seedlings either in the presence or absence of Zn. The four bacterial strains significantly increased the concentration of water-extractable Zn compared with axenic soil. In addition, the four Zn-tolerant bacteria significantly increased the shoot biomass and Zn accumulation in O. violaceus compared to non-inoculated plants. The bacterial strains displayed different capacities to enhance plant Zn accumulation. Flavobacterium sp. was identified as the best candidate for enhancing Zn accumulation in plants, increasing Zn accumulation up to 1.21- and 1.19-fold in shoots and roots, respectively, compared to non-inoculated plants. It was indicated that Zn-tolerant bacteria played an important role in influencing the availability of water-soluble Zn in soil and Zn accumulation by plants. This study provides insight into the development of plant–microbe systems for phytoremediation.     

Application of plant growth-promoting endophytes (PGPE) isolated from Solanum nigrum L. for phytoextraction of Cd-polluted soils

Many plant growth-promoting endophytes (PGPE) can assist their host plants cope with contaminant-induced stress responses, which can improve plant growth. In this study, four heavy metals resistant endophytic bacteria, Serratia nematodiphila LRE07, Enterobacter aerogenes LRE17, Enterobacter sp. LSE04 and Acinetobacter sp. LSE06, were isolated from Cd-hyperaccumulator Solanum nigrum L. grown in metal-polluted soil. Their plant growth promoting properties such as production of 1-aminocyclopropane-1-carboxylic (ACC) deaminase, indole-3-acetic acid (IAA), siderophores and phosphate solubilizing activity were characterized in vitro. When added to the Cd-amended soils, all of these four bacteria significantly increased Cd extraction from the soils. Subsequently, a pot experiment was conducted to elucidate the effects of inoculating of these PGPE on the plant growth and Cd uptake by S. nigrum L. grown in three different levels of Cd-contaminated soils. Results showed that the inoculation with these PGPE not only stimulated the growth of host plant, but also influenced the accumulation of Cd in the root, stem and leaf tissue of S. nigrum L. All four strains could colonize the rhizosphere soil and even some can be found in plant interior tissues. The present observations demonstrated that PGPE were valuable microorganism resource which can be exploited to improve the efficiency of phytoextraction.     

Lyophyllum sp. strain Karsten alleviates pH pressure in acid soil and enhances the survival of Variovorax paradoxus HB44 and other bacteria in the mycosphere

In previous work, Variovorax paradoxus strain HB44, next to Burkholderia terrae BS001 and Dyella japonica BS003, were found to be selected in the mycosphere of the tricholomataceous fungi Laccaria proxima and Lyophyllum sp. strain Karsten in an acid soil denoted G. V. paradoxus HB44 showed poor survival in G bulk soil, irrespective of prior soil sterilization, and this poor survival also occurred for B. terrae BS001 and D. japonica BS003. In contrast, the survival rate of strain HB44 in two other soils, with pH values > 5.5, was significantly raised. Also, significantly enhanced strain HB44 survival in G soil was found if the pH was raised to 5.5 or 6.5, and it was even shown to grow (in the presence of the exogenous carbon source glycerol) at such pH values in the sterile G soil. This behaviour was similar to that of the V. paradoxus type strain. Strikingly, Lyophyllum sp. strain Karsten, when colonizing the sterilized G soil, significantly raised the soil pH from about 4.6 to ≥5.0. The pH raise was dependent on time, hyphal development, as well as on initial soil pH, but was consistent throughout. The modulated soil pH conditions were shown to be permissive for the survival and growth of strain HB44, and this was extended to strains BS001 and BS003. These findings corroborate the hypothesis that L. sp. strain Karsten provides a suitable habitat for acid-sensitive strains like HB44, BS001 and BS003 in its mycosphere in acid soil, which is strongly defined by the establishment of a growth-permissive pH.     

Isolation of Cadmium-Resistant Bacteria and Their Resistance Mechanisms

In the first series of studies aimed at addressing the environmental problems of soils and drainage systems, we attempted to isolate cadmium (Cd)-resistant bacteria from soils heavily contaminated with Cd and determine their growth rate in media with cadmium. In soils contaminated with heavy metals, there was on increase in the number of Cd-resistant bacteria. Among 14 Cd-resistant bacteria isolated from soils contaminated with heavy metals, only six strains (Flavobacterium sp., Comamonas testosteronii, Methylobacterium fujisawaense, Alcaligenes piechaudii, Alcaligenes xylosoxidans) were identified as new types of Cd-resistant bacteria. All the isolated resistant bacteria grew fast, and reached the maximum growth rates within 24 to 48 h (Growth conditions were as follows. Culture medium: nutrient broth, pH: 6.0, temperature: 30°C and of concentration of added Cd: 0.1, 1.0, 10.0, and 100.0 mg kg^-1).     

盐胁迫油菜根际中含假单胞菌（Pseudomonas spp.1）的氨基环丙烷-1-羧酸 (ACC) 脱氨基酶特征研究

When exposed to biotic or abiotic stress conditions,plants produce ethylene from its immediate precursor 1-aminocyclopropane-1-carboxylate(ACC),leading to retarded root growth and senescence.Many plant growth-promoting rhizobacteria contain the enzyme ACC deaminase and this enzyme can cleave ACC to form α-ketobutyrate and ammonium,thereby lowering levels of ethylene.The aim of this study was to isolate and characterize ACC deaminase-producing bacteria from the rhizosphere of salt-stressed canola(Brassica napus L.).Out of 105 random bacterial isolates,15 were able to utilize ACC as the sole source of nitrogen.These 15 isolates were also positive for indole acetic acid(IAA) production.Phylogenetic analysis based on partial 16 S rDNA sequences showed that all isolates belonged to fluorescent Pseudomonas spp.In the canola rhizosphere investigated in this study,Pseudomonas fluorescens was the dominant ACC deaminase-producing species.Cluster analysis based on BOX-A1R-based repetitive extragenic palindromic-polymerase chain reaction(BOX-PCR) patterns suggested a high degree of genetic variability in ACC deaminase-producing P.fluorescens strains.The presence of indigenous ACC-degrading bacteria in the rhizosphere of canola grown in saline soils indicates that these bacteria may contribute to salinity tolerance.     

Characterization of brushite as a re-crystallization product formed during bacterial solubilization of hydroxyapatite in batch cultures

Two strains of bacteria (Burkholderia sp., strain FeGL01, and Burkholderia caribiensis, strain FeGL03) were isolated from a Brazilian high phosphorus iron ore. The capacity of both strains to solubilize hydroxyapatite, Ca₅(PO₄)₃(OH), was assessed in plate and batch cultures. In batch cultures, the concentration of solution-P showed two kinetics: an initial one, characterized by a continuously increasing kinetics and a second one, characterized by oscillatory kinetics. To understand the nature of these oscillations, phosphatic residues in the spent broth were collected before, during and after the oscillations, and characterized using scanning electron microscopy (SEM), energy-dispersive X-ray chemical microanalyses (EDX) and X-ray diffraction (XRD). From these studies, it was found that drops in P concentration were related to the formation of an intermediate phosphate in the residues, identified as brushite, CaHPO₄·2H₂O. Later increase of available P in the solution was found to be a consequence of re-dissolution of brushite crystals previously formed. Re-crystallization of brushite was also detected in plate cultures after 12-14 days of incubation     

Vigna radiata var. GM4 Plant Growth Enhancement and Root Colonization by a Multi-Metal-Resistant Plant GrowthPromoting Bacterium Enterobacter sp. C1D in Cr(VI)-Amended Soils

Contamination of agricultural soils by heavy metals has become a major concern due to their toxic effects on plant growth, symbiosis and consequently the yields of crops. In the present study, to enhance plant growth in Cr(VI)-amended soils, novel metalresistant plant growth-promoting bacteria (PGPB) were isolated from a soil contaminated with industrial waste effluent. One of the bacterial isolates, identified as Enterobacter sp. C1D by 16S rRNA gene sequencing, was found to be multi-metal resistant in nature with excellent plant growth-promoting (PGP) traits. Mung bean (Vigna radiata var. GM4) inoculation with Enterobacter sp. C1D significantly (P < 0.01) increased root and shoot length, shoot and root weight, and chlorophyll content in a range of Cr(VI) treatments. Plant tolerance towards Cr(VI) measured as effective concentration showed higher values with Enterobacter sp. C1Dtreated plants compared to un-inoculated plants. Root colonization study was also carried out using green fluorescence protein-labeled Enterobacter sp. C1D under a hydroponic system. Confocal laser scanning microscopy of the plant roots showed heavy bacterial loads on the surface of the plant root specifically at the root tip and the point of root hair/lateral root formation. The results of PGP traits showed that elevated indole acetic acid levels and 1-aminocyclopropane-1-carboxylate deaminase activity enabled Enterobacter sp. C1D to enhance V. radiata growth in Cr(VI)-amended soils, whereby it significantly increased plant tolerance towards elevated Cr(VI) concentrations.     

Selection of Variovorax paradoxus-like bacteria in the mycosphere and the role of fungal-released compounds

At two occasions (2004 and 2006), a similar cluster of culturable bacteria was found to be selected in the mycosphere of the basidiomycetous fungus Laccaria proxima (Agaricales, Tricholomataceae) in the field. The bacteria, identified as related to Variovorax paradoxus, comprised 7.3-9% of the total culturable bacterial community in the L. proxima mycosphere, but were not found in corresponding bulk soil (<0.3%). One strain, denoted HB44, was selected in order to unravel the basis of the V. paradoxus mycosphere competence in in vitro experiments with the former Laccaria laccata, which was recently reclassified as Lyophyllum sp. strain Karsten (Agaricales, Tricholomataceae). In liquid culture experiments, L. strain Karsten was shown to be an avid producer of glycerol, next to acetate and formate, which constituted the most abundant carbonaceous compounds released. Strain HB44 was able to grow avidly at the expense of the glycerol liberated by the fungus, as evidenced by proton NMR analysis of the fungal exudates in the medium before and after bacterial growth. In sterilized field soil, strain HB44 survived significantly better in the presence than in the absence of L. strain Karsten. Addition of a glycerol series to the sterilized soil (without the fungus) resulted in the persistence or growth of strain HB44, but only if the pH of this soil was previously set at 5.5. Thus, we provide evidence for the contention that tricholomataceous fungi can create specific niches in soil for the V. paradoxus-related strain HB44 and that glycerol may be a main carbon source that drives the selection of this organism.     

Isolation and characterization of plant growth promoting endophytic bacterial isolates from root nodule of Lespedeza sp.

Thirty-nine endophytic bacterial strains were isolated from the nodule of Lespedeza sp. grown in two different locations of South Korea. All strains were checked for their plant growth promoting (PGP) abilities under in vitro conditions. Most of the isolates showed multiple PGP activity, i.e., indole acetic acid production, ACC deaminase activity, siderophore production, and phosphate solubilization. The strains were identified by using 16S rRNA gene sequence analysis as belonging to Alphaproteobacteria, Betaproteobacteria, Actinobacteria, and Firmicutes phylum with nine different genera Arthrobacter, Bacillus, Bradyrhizobium, Burkholderia, Dyella, Methylobacterium, Microbacterium, Rhizobium, and Staphylococcus. Gene nodA amplification showed positive results only for strains from Bradyrhizobium and Rhizobium genera. The strains from Bradyrhizobium and Rhizobium genera enhanced plant growth, nodulation, and acetylene reduction activity when inoculated on Vigna unguiculata L. (cowpea), whereas other strains did not induce nodule formation but enhanced plant growth. Herbaceous legume Lespedeza sp. formed root nodules with diverse bacterial group, and probably, these bacteria can be used for stimulating plant growth.     

Improvement of Brassica napus growth under cadmium stress by cadmium-resistant rhizobacteria

This study focuses on the characterization of four bacterial isolates from heavy metal-polluted rhizosphere in order to examine their plant growth promoting (PGP) activity. The PGP activity on the canola (Brassica napus) of the strains which showed cadmium resistance and multiple PGP traits was assessed in the presence and in the absence of Cd²⁺. The strains, Pseudomonas tolaasii ACC23, Pseudomonas fluorescens ACC9, Alcaligenes sp. ZN4 and Mycobacterium sp. ACC14 showed 1-aminocyclopropane-1-carboxylate deaminase (ACCD) activity. They also synthesized ACCD enzyme in vitro when 0.4 mM Cd²⁺ was added to the growth medium. The presence of the metal, however, reduced the ACCD activity in Alcaligenes sp. ZN4 and Mycobacterium sp. ACC14, while it did not affect the ACCD activity of P. tolaasii ACC23 and P. fluorescens ACC9. ACC9 and ACC23 produced indole acetic acid (IAA) and siderophores, while ACC14 produced only IAA. IAA and siderophores were produced more actively under Cd-stress.Root elongation assays conducted on B. napus under gnotobiotic conditions demonstrated increases (from 34% up to 97%) in root elongation of inoculated canola seedlings compared to the control plants. Subsequently, the effect of inoculation with these strains on growth and uptake of Cd²⁺ in roots and shoots of canola was studied in pot experiments using Cd-free and Cd-treated (15 μg Cd²⁺ g^?1 dw) soil. Inoculation with P. tolaasii ACC23, P. fluorescens ACC9 and Mycobacterium sp. ACC14 promoted the growth of plants at concentrations of 0 and 15 μg Cd²⁺ g^?1 soil. The maximum growth was observed in the plants inoculated with P. tolaasii ACC23. The strains did not influence the specific accumulation of cadmium in the root and shoot systems, but all increased the plant biomass and consequently the total cadmium accumulation.The present observations showed that the bacterial strains used in this study protect the plants against the inhibitory effects of cadmium, probably due to the production of IAA, siderophores and ACCD activity.     

Physiological enhancement of early growth of rice seedlings (Oryza sativa L.) by production of phytohormone of N2-fixing methylotrophic isolates

Three plant-growth promoting, N₂-fixing methylotrophic strains isolated from rice cultivars (Oryza sativa L.), viz, Methylobacterium sp. CBMB20, Enterobacter sp. CBMB30, Burkholderia sp. CBMB40, were selected, and their activities in promoting the early growth of rice were studied. Seeds treated with the methylotrophic strains improved seed germination, seedling vigor index (SVI), and biomass of rice seedlings. The methylotrophic population in the treated seedlings increased in the vegetative stages when compared to seeding stages. Treated seedlings showed a higher accumulation of plant hormones viz trans-zeatin riboside, isopentenyladenosine, and indole-3-acetic acid than untreated seedlings. Plant hormones were detected immunologically using the phytodetek kit. Conformational evidence suggested that cytokinins were produced by the epiphytic bacteria colonizing the plants rather than by the plants themselves. In addition, the inoculated early stage rice seedlings also exhibited a wide range of acetylene reduction activity. The results suggest the potential use of these bacteria to stimulate germination, SVI, and biomass production, which is mediated by production of plant hormone accumulation and nitrogen fixation.     

Grazing by nematodes on rhizosphere bacteria enhances nitrate and phosphorus availability to Pinus pinaster seedlings

The microbial loop is thought to play a major role in the mineralization of nutrients such as nitrogen (N) and phosphorus (P) in terrestrial ecosystems. This microbial loop is based on the grazing of bacteria by predators such as bacterial-feeding nematodes. However, little is known about the impact of grazing by nematodes on the mineral nutrition of woody plants. This study was undertaken to quantify the effect of nematode grazing on bacteria in the rhizosphere on the root architecture, growth and mineral nutrition (N and P) of a woody species (Pinus pinaster). Young P. pinaster seedlings were cultivated for 35 days in a simplified sterile experimental system with bacteria (Bacillus subtilis) and bacterivorous nematodes (Rhabditis sp.) isolated from soil samples collected from a 15-year old stand of maritime pine. To check the hypothesis that bacteria could be a source of nutrients, especially N, two N sources were supplied in the medium: (i) bacterial N labeled with ¹⁵N and (ii) nitrate. Phosphorus was supplied as insoluble inorganic tri-calcium phosphate (TCP). The results showed that the ¹⁵N flow from the bacteria to the plant shoots was only significant when nematodes were present, with an average accumulation of 14 ± 5 μg plant⁻¹ of ¹⁵N. Plants cultivated with nematodes also accumulated significantly more total N in their shoots than sterile ones or inoculated with bacteria, resulting in a net average increase in N of 700 μg plant⁻¹. The same result was observed for the total P accumulation in the shoots, as plants with nematodes accumulated an average of 300 μg plant⁻¹ more P than sterile ones or inoculated with bacteria. However, the presence of bacteria, whether alone or with nematodes, did not modify the root architecture. These results demonstrated that the presence of bacterial-feeding nematodes significantly enhanced N and P availability to P. pinaster seedlings, probably by improving plant use of nitrate and insoluble P supplied in the medium.     

Characterization of Heavy Metal-Resistant Endophytic Yeast Cryptococcus sp. CBSB78 from Rapes (Brassica chinensis) and Its Potential in Promoting the Growth of Brassica spp. in Metal-Contaminated Soils

A Cd-, Pb-, Zn-, Cu-resistant endophytic yeast CBSB78 was isolated from surface-sterilized rape roots. The isolate was identified as Cryptococcus sp. based on the ITS1?C5.8S?CITS2 sequence analysis. The strain was resistant to 20 mM Cd²⁺, 20 mM Pb²⁺, 10 mM Zn²⁺, and 7 mM Cu²⁺. The yeast CBSB78 was a low indole-3-acetic acid (IAA) producer and possessed low 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity. Overall, 29.4?C244 % of survival rates increased and the dry weight of Brassica alboglabra showed a 41.1 % increase when it was inoculated into the seedlings. The inoculation of CBSB78 could also increase the extraction amounts of Cd, Pb, and Zn by B. alboglabra simultaneously in the multi-metal contaminated soils, which showed the potential to improve extraction efficacy of Cd, Pb, Zn by B. alboglabra seedlings in the field.     

Isolation and characterisation of symbiotically effective Rhizobium resistant to arsenic and heavy metals after the toxic spill at the Aznalcóllar pyrite mine

After the toxic spill occurred at Aznalcóllar pyrite mine (Southern Spain), a wide area of croplands near the Doñana Wild Park was contaminated with 4.5 million m³ of slurries composed of acidic waters loaded with toxic metals and metalloids such as As, Sb, Zn, Pb, Cu, Co, Tl, Bi, Cd, Ag, Hg and Se. Today, 6 years after the spill, the concentration of toxic elements in these soils is still very high, in spite of the efforts to clean the zone. However, some plant species have colonised this contaminated area. Legumes possessing N₂-fixing nodules on their roots represented a significant proportion of these plants. Our objective was to use the Rhizobium-legume symbiosis as a new tool for bioremediate the affected area. We have isolated about 100 Rhizobium strains, 41 of them being resistant to high concentrations of As (300 mg l⁻¹), Cu (100 mg l⁻¹) and Pb (500 mg l⁻¹). Their phenotypes and bioaccumulation potentials have been characterised by their growth rates in media supplemented with As and heavy metals. The presence of the resistance genes in some strains has been confirmed by PCR and Southern blot hybridisation. Several Rhizobium were symbiotically effective in the contaminated soils. On the other hand, the first steps in nodule establishment seemed to be more affected by heavy metals than N₂-fixation.     

镉诱导拟南芥根尖过氧化氢积累导致植物根生长抑制

以模式植物拟南芥为材料研究了植物主根对不同浓度镉胁迫的响应。结果表明,随镉浓度的升高,植物主根生长受到明显抑制,胎盘兰染色表明高剂量的镉造成主根根尖细胞死亡。进一步二氨基联苯胺(DAB)染色发现镉胁迫诱导植物根尖大量积累过氧化氢,而在胁迫培养基中加入维生素C可显著改善植物根的生长、降低过氧化氢积累,并减少镉诱导的根尖细胞死亡。上述结果表明,镉胁迫诱导的拟南芥主根生长抑制很可能是由于根尖细胞过氧化物积累所致。     

Solubilization of insoluble inorganic zinc compounds by ericoid mycorrhizal fungi derived from heavy metal polluted sites

Ericoid mycorrhizal fungi increase the ability of their host plants to colonize soils polluted with toxic metals, although the underlying mechanisms are not clearly understood. Two mycorrhizal strains of Oidiodendron maius isolated from contaminated soil were previously shown to tolerate high concentrations of toxic metals. We investigated further the biological mechanisms that may explain metal tolerance, focussing on the interactions between insoluble metal species and extracellular fungal metabolites. In particular, we demonstrate that fungal strains derived from polluted and unpolluted soils mobilize insoluble inorganic zinc compounds to different extents. Strains from polluted soils showed in fact little ability to solubilize Zn from both ZnO and Zn₃(PO₄)₂, whereas strains from unpolluted soils showed a higher solubilization potential. This different behaviour was confirmed when the solubilization abilities of a wider range of fungal strains (25 isolates) was examined. Induction of organic acids (malate and citrate) by the metal compounds was at least in part responsible for metal solubilization. Our results suggest that ericoid mycorrhizal strains from polluted and unpolluted soils may interact differently with metal compounds. We speculate that this may reflect specific strategies to maintain homeostasis of essential metals under different soil conditions.     

Characterization of copper-resistant bacteria and assessment of bacterial communities in rhizosphere soils of copper-tolerant plants

Thirteen copper-resistant bacteria were isolated from copper-tolerant plant species growing on a copper mine wasteland. The isolates were identified by 16S rRNA gene sequence analysis and characterized by their resistance to heavy metals and plant growth-promoting characteristics. The assessment of the bacterial communities in the rhizosphere soils of copper-tolerant plants was measured as bands in denaturing gradient gel electrophoresis (DGGE) obtained directly from rhizosphere soil DNA extracts. The isolates were found to exhibit different multiple heavy metal resistance characteristics. Strains SZY6, YJ7 and JYC17 were found to produce indole acetic acid (IAA), siderophore, 1-aminocyclopropane-1-carboxylate (ACC) deaminase or to solubilize phosphate. Root elongation assay conducted on rape under gnotobiotic conditions with strains MT16, JYC17, SZY6, GZC24, and YJ7 demonstrated increase (from 16 to 41%) in root elongation of inoculated rape seedlings compared to the control plants. In the rhizosphere soil samples the DGGE profiles of the direct DNA extracts were similar. The DGGE profiles indicated that there was no significant correlation between the concentration of available copper in the rhizosphere soils and the number of the visible bands in the DGGE pattern.     

Metal-tolerant bacteria occurring in heavily polluted soil and mine spoil

The abundance of metal-tolerant populations among culturable bacterial communities in arable soils of different texture and barren spoil of a former silver mine was determined. In addition, bacterial isolates were identified by MIDI-FAME profiling of total-cell fatty acids and plasmid-encoded tolerance to selected heavy metals, as well as the metal-tolerance patterns of the plasmid-containing isolates were ascertained. The difference in the bacterial numbers between the sandy-loam and clay soils was found, which was associated with the effect of higher concentrations of heavy metals, both total and soluble fractions, in the clay soil. The high proportions of metal-tolerant populations in both soils and the spoil were ascertained. In both soils, the bacterial isolates were mostly represented by Gram-negatives, and Variovorax paradoxus dominated in the spoil. Several isolates contained plasmids of the same size, however, only the tolerance to Zn and Cd appeared to be associated with the plasmids, as showed by the transformation data. Minimal inhibitory concentration (MIC) data indicated that the plasmid-containing isolates developed tolerance to several metals tested. Such isolates as Methylobacterium mesopilicum and Flavobacterium from the sandy-loam soil, Pseudomonas gladioli from the clay soil and V. paradoxus from the spoil could be of great interest because of their high tolerance to Zn, Cu, Cd, or Ag, respectively.     

Gram-negative bacterial flora on the root surface of wheat (Triticum aestivum) grown under different soil conditions

We identified 161 Gram-negative bacterial strains isolated from the root surface of wheat grown under different soil conditions. The strains were divided into seven groups based on major morphological and physiological properties. Taxonomic allocation of the groups was verified by guanine+cytosine contents of DNA. Except for one group, which may be assumed to include bacteria belonging to the genera Flavobacterium and Cytophaga, the various groups were taxonomically united. The distribution of the groups changed with soil improvement. Pseudomonads predominated in unimproved soil, but Flavobacterium and Cytophaga spp. were predominant in the most improved soil. As all the strains were non-fermentative by Hugh and Leifson's test, API 20NE identification was applied. However, many strains were misidentified by this system, especially in the Flavobacterium and Cytophaga spp. group. For ecological studies, the strains were classified to species level by the API 20 NE system and by the results of a combination of guanine+cytosine (mol%) and isoprenoid quinone data. The pattern of distribution of the bacteria on the root surface of wheat varied at species level within one genus depending on soil conditions.Dedicated to Professor J. C. G. Ottow on the occasion of his 60th birthday     

Heavy metal content and toxicity of mine and quarry soils

Purpose

Soils formed in metallic mines and serpentinite quarries, among other unfavourable features, have high levels of heavy metals. They can release into the environment causing surface and subsurface water contamination, uptake by plants, their accumulation in the food chain and adverse effects on living organisms. In this work, we studied the magnitude of the soils’ toxic effects not only on spontaneous plants but also on two species with phytoremediation potential.

Materials and methods

Several soils from two different exploitations were selected: a lead and zinc mine and a serpentinite quarry. Soils were characterized, and the pseudo-total and extractable contents of Co, Cr and Ni in soils from a serpentinite quarry were determined. The Cd, Pb and Zn pseudo-total and extractable contents were determined in soils developed in the Pb/Zn abandoned mine. Using a biotest, the chronic toxicity of the soil samples on higher plants was determined. Festuca ovina L., Cytisus scoparius (L.) Link., Sinapis alba L. and Brassica juncea L. were selected, the first two because they are spontaneous plants in the study areas and the last two because they have heavy metal phytoremediation potential.

Results and discussion

Pseudo-total contents of Co, Cr and Ni in the serpentinite quarry soils and of Zn, Pb and Cd in the Zn/Pb mine soils exceed generic reference levels. CaCl₂ is the reactant that extracts the highest proportion of Co, Cr and Ni in the quarry soils and EDTA the largest proportion of Pb Zn and Cd content in the mine soils. The germination index values based on seed germination and root elongation bioassays revealed increasing plant sensitivity to the mine soils in the following order: B. juncea?<?S. alba?<?F. ovina?<?C. scoparius. The wide range of GI values indicates that the response of test plants to soil heavy metals depended on their concentrations and soil characteristics, especially pH and organic matter content.

Conclusions

The pollution index indicates severe Cd, Pb and Zn contamination in the mine soils, as well as high Cr and Ni and moderate Co contamination in the serpentinite quarry soils. The performed biotests were suitable for identifying toxic soils and showed that the studied soils are toxic to the spontaneous plants, more to C. scoparius than to F. ovina. They also indicate that the mine soils are more toxic than the quarry soils for both species.