Biological activity and colonization pattern of the bioluminescence-labeled plant growth-promoting bacterium Kluyvera ascorbata SUD165/26

Kluyvera ascorbata SUD165/26 is a spontaneous siderophore-overproducing mutant of K. ascorbata SUD165, which was previously isolated from nickel-contaminated soil and shown to significantly enhance plant growth in soil contaminated with high levels of heavy metals. To develop a better understanding of the functioning of K. ascorbata SUD165/26 in the environment, and to trace its distribution in the rhizosphere, isolates of this bacterium were labeled with either green fluorescent protein or luciferase. When the plant growth-promoting activities of the labeled strains were assayed and compared with the activities of the unlabeled strain, none of the monitored parameters had changed to any significant extent. When the spatial colonization patterns of the labeled bacteria on canola roots were determined after seed application, it was observed that the bacterium was tightly attached to the surface of both roots and seeds, and formed aggregates. The majority of the bacterial population inhabited the upper two thirds of the roots, with no bacteria detected around the root tips.     

A Plant Growth-Promoting Bacterium That Decreases Nickel Toxicity in Seedlings

A plant growth-promoting bacterium, Kluyvera ascorbata SUD165, that contained high levels of heavy metals was isolated from soil collected near Sudbury, Ontario, Canada. The bacterium was resistant to the toxic effects of Ni²⁺, Pb²⁺, Zn²⁺, and CrO₄⁻, produced a siderophore(s), and displayed 1-aminocyclopropane-1-carboxylic acid deaminase activity. Canola seeds inoculated with this bacterium and then grown under gnotobiotic conditions in the presence of high concentrations of nickel chloride were partially protected against nickel toxicity. In addition, protection by the bacterium against nickel toxicity was evident in pot experiments with canola and tomato seeds. The presence of K. ascorbata SUD165 had no measurable influence on the amount of nickel accumulated per milligram (dry weight) of either roots or shoots of canola plants. Therefore, the bacterial plant growth-promoting effect in the presence of nickel was probably not attributable to the reduction of nickel uptake by seedlings. Rather, it may reflect the ability of the bacterium to lower the level of stress ethylene induced by the nickel.     

Proteomic analysis of the response of the plant growth-promoting bacterium Pseudomonas putida UW4 to nickel stress

Background  

Plant growth-promoting bacteria can alleviate the inhibitory effects of various heavy metals on plant growth, via decreasing levels of stress-induced ethylene. However, little has been done to detect any mechanisms specific for heavy metal resistance of this kind of bacteria. Here, we investigate the response of the wild-type plant growth-promoting bacterium Pseudomonas putida UW4 to nickel stress using proteomic approaches. The mutant strain P. putida UW4/AcdS^-, lacking a functional 1-aminocyclopropane-1-carboxylic acid deaminase gene, was also assessed for its response to nickel stress.     

Metal tolerance in tissue cultures of anthoxanthum odoratum

Tissue cultures were initiated from one non-tolerant (S20) and two zinc and lead tolerant (T92 and T94) clones of Anthoxanthum odoratum. Growth of callus from the non-tolerant clone was reduced by the presence of zinc, lead, copper and nickel, whereas callus from the two tolerant clones showed no reduction of growth in the presence of zinc and lead but growth was reduced by copper and nickel. The specificity of metal tolerance shown by the parental material was maintained in the callus. Tolerant and non-tolerant callus accumulated similar amounts of zinc and lead.     

Concentrations of Trace Metals in Dominant Aquatic Plants of the Lake Provala (Vojvodina, Yugoslavia)

The trace metal (Fe, Mn, Zn, Cu, Ni, Pb, Cd, Sr, and Cr) contents in the most common submerged and floating aquatic plants Ceratophyllum demersum L., Myriophyllum spicatum L., and Nymphoides flava Hill. of Provala Lake were evaluated. Considerable higher contents of iron, manganese, zinc, nickel, lead and strontium were found in submerged species than in the floating ones. The presence of cadmium and lead in plant tissues points to a certain degree of lake water pollution.     

Assessing Plant Phytoextraction Potential Through Mathematical Modeling

One of the most serious and long-term consequences of environmental pollution is heavy metal contamination of soils. Elements such as zinc, cadmium, lead, nickel, and chromium are being released into the environment by many industrial processes and have now reached concentrations that are of concern. Phytoremediation is a new, low-cost, and environmentally friendly technique that relies on the natural properties of some plants to clean-up the ground through their ability to take up metals from the soil. Hyperaccumulator plants, capable of accumulating metals far in excess of any normal physiological requirement, represent a most promising tool for metal phytoextraction, but the in field establishment of their conditions for utilization needs a long period because of the plant life-cycle. The use of a mathematical model is proposed to process growth and uptake data from in vitro experiments for a rapid assessment of the time and concentration parameters for the deployment of hyperaccumulator plants for phytoextraction purposes. This preliminary research has been carried out using Alyssum bertolonii Desv., a nickel hyperaccumulator endemic to Italian serpentine soils.     

Burkholderia sp. SCMS54 reduces cadmium toxicity and promotes growth in tomato

Cadmium (Cd) can enter soil through the use of fertilisers, calcareous, pesticides and industrial and/or domestic effluents. Cd can leach into groundwater and be taken up by plants, potentially leading to reductions in plant growth and yield. In soil, plant roots interact with heavy metal (HM)‐tolerant microorganisms that may promote plant growth. Soil microorganisms may also be able to solubilise or mobilise soil metals, thereby acting as bioremediators. A better understanding of the interaction among plants, metals, microorganisms and soil will lead to improved plant tolerance. Two multi‐tolerant bacteria from the Burkholderia genus were isolated from Cd‐contaminated and Cd‐uncontaminated soil of a coffee plantation. In addition to its high tolerance to Cd, the strain SCMS54 produces indole‐acetic acid (IAA), solubilises inorganic phosphate and produces siderophores, demonstrating its potential to contribute to beneficial plant–microorganism interactions. When interacting with tomato plants exposed to Cd, the bacterium led to decreases in plant peroxide and chlorosis levels, promoted relative plant growth and decreased the root absorption of Cd, resulting in increased plant tolerance to this highly toxic HM. The results indicated that the inoculation of tomato plants with Burkholderia sp. SCMS54 promotes better growth in plants cultivated in the presence of Cd. This phenomenon appears to be attributed to a mechanism that decreases Cd concentrations in the roots via a beneficial interaction between the bacteria and the plant roots.     

Hydroxamate siderophores produced by Streptomyces acidiscabies E13 bind nickel and promote growth in cowpea (Vigna unguiculata L.) under nickel stress

The siderophore-producing ability of nickel-resistant Streptomyces acidiscabies E13 and the role of the elicited siderophores in promoting plant growth under iron and nickel stress are described. Siderophore assays indicated that S. acidiscabies E13 can produce siderophores. Electrospray ionization mass spectrometry (ESI-MS) revealed that the bacterium simultaneously produces 3 different hydroxamate siderophores. ESI-MS showed that in addition to iron, all 3 siderophores can bind nickel. In vitro plant growth tests were conducted with cowpea (Vigna unguiculata) in the presence and absence of the elicited siderophores. Culture filtrates containing hydroxamate siderophores significantly increased cowpea height and biomass, irrespective of the iron status of the plants, under nickel stress. The presence of reduced iron was found to be high in siderophore-containing treatments in the presence of nickel. Measurements of iron and nickel contents of cowpea roots and shoots indicated that the siderophore-mediated plant growth promotion reported here involves the simultaneous inhibition of nickel uptake and solubilization and supply of iron to plants. We conclude that hydroxamate siderophores contained in culture filtrates of S. acidiscabies E13 promoted cowpea growth under nickel contamination by binding iron and nickel, thus playing a dual role of sourcing iron for plant use and protecting against nickel toxicity.     

Increasing <Emphasis Type="Italic">Triticum aestivum</Emphasis> tolerance to cadmium stress through endophytic strains of <Emphasis Type="Italic">Bacillus subtilis</Emphasis>

Impact of inoculation of wheat seeds with endophytic strains of B. subtilis bacterium on revealing cadmium phytotoxicity of the plants was investigated. It was shown that, in the presence of Cd in the plants whose seeds were inoculated with the above bacteria, the activities of catalase and peroxidase and the content of nonprotein thiols were increased, while an intensity of lipid peroxidation decreased. Moreover, inoculation of plant seeds with the bacteria contributed to lowering the metal content in plant shoots.     

Über die Kallosebildung in Siebröhren von Kartoffelpflanzen in Abhängigkeit von Blattrollvirusinfektion und chemisch-physikalischen Bedingungen

All the cultivars of tomato tested were found to be infected with the root‐knot nematode, Meloidogyne incognita, however, to varying extent. There was also reducton in plant growth parameters accordingly. Further reduction in plant growth of tomato cultivars was recorded when plants also received the treatment with the heavy metal, lead, notwithstanding the fact that the presence of lead also reduced the root‐knot development. Tomato cv. Arka Vikas showed minimum reduction in plant growth with single or combined treatment with the nematode and the heavy metal.     

Siderophores mediate reduced and increased uptake of cadmium by Streptomyces tendae F4 and sunflower (Helianthus annuus), respectively

Aims: As a toxic metal, cadmium (Cd) affects microbial and plant metabolic processes, thereby potentially reducing the efficiency of microbe or plant‐mediated remediation of Cd‐polluted soil. The role of siderophores produced by Streptomyces tendae F4 in the uptake of Cd by bacteria and plant was investigated to gain insight into the influence of siderophores on Cd availability to micro‐organisms and plants. Methods and Results: The bacterium was cultured under siderophore‐inducing conditions in the presence of Cd. The kinetics of siderophore production and identification of the siderophores and their metal‐bound forms were performed using electrospray ionization mass spectrometry. Inductively coupled plasma spectroscopy was used to measure iron (Fe) and Cd contents in the bacterium and in sunflower plant grown in Cd‐amended soil. Siderophores significantly reduced the Cd uptake by the bacterium, while supplying it with iron. Bacterial culture filtrates containing three hydroxamate siderophores secreted by S. tendae F4 significantly promoted plant growth and enhanced uptake of Cd and Fe by the plant, relative to the control. Furthermore, application of siderophores caused slightly more Cd, but similar Fe uptake, compared with EDTA. Bioinoculation with Streptomyces caused a dramatic increase in plant Fe content, but resulted only in slight increase in plant Cd content. Conclusion: It is concluded that siderophores can help reduce toxic metal uptake in bacteria, while simultaneously facilitating the uptake of such metals by plants. Also, EDTA is not superior to hydroxamate siderophores in terms of metal solubilization for plant uptake. Significance and Impact of the Study: The study showed that microbial processes could indirectly influence the availability and amount of toxic metals taken up from the rhizosphere of plants. Furthermore, although EDTA is used for chelator‐enhanced phytoremediation, microbial siderophores would be ideal for this purpose.     

Isolation of a naturally-occurring nickel resistance plasmid from a rare hypersaline estuary (Laguna Madre,Texas, USA) for potential use as a bio-indicator of metal contamination

Metal-resistant bacteria were isolated from sediments of the Laguna Madre, a rare hypersaline estuary impacted by many anthropogenic compounds, including various metals and metalloids. Bacteria were initially isolated on nutrient agar supplemented with NaCl; random isolates (n = 100) were tested for metal resistance toward zinc, nickel, chromium, and cadmium using a pour plate disc assay. Metal-resistant cultures were assayed for plasmids that contained naturally-occurring heavy metal resistance genes. Putative metal-resistance plasmids were tested for metal-resistance efficacy by transforming a metal-sensitive strain of Escherichia coli. Polymerase Chain Reaction (PCR) primers were designed to detect cnrA, part of a nickel–cobalt resistance gene cluster, and restriction endonuclease digests were performed to detect restriction sites within the plasmid. Results showed that many bacterial isolates tested were resistant toward most of the metals used in this study. Among tested bacteria cultures, 34 were resistant to zinc, 64 were resistant to chromium, and 51 resistant to cadmium. Only 8 cultures were resistant to nickel; however, most bacteria were found to be resistant to more than one metal. Several plasmids were found from the bacteria isolates. One plasmid, designated pDZ5, was isolated from a bacterium identified as Bacillus pumilus by 16S rRNA sequencing. Plasmid pDZ5 conferred nickel resistance to the metal-sensitive E. coli strain and was found to contain cnrA as confirmed by PCR amplification. Plasmid pDZ5 was successfully cut with restriction enzymes for potential ligation with reporter genes. The presence, abundance and expression of pDZ5 may prove to be a useful bio-indicator of metal contamination, specifically nickel pollution, in the Laguna Madre due to the fewer number of bacteria that were nickel-resistant compared to other metals.     

Fidelity of metal insertion into hydrogenases.

The fidelity of metal incorporation into the active center of hydrogenase 3 from Escherichia coli was studied by analyzing the inhibition of the maturation pathway by zinc and other transition metals. Hydrogenase maturation of wild-type cells was significantly affected only by concentrations of zinc or cadmium higher than 200 microM, whereas a mutant with a lesion in the nickel uptake system displayed a total blockade of the proteolytic processing of the precursor form into the mature form of the large subunit after growth in the presence of 10 microM Zn(2+). The precursor could not be processed in vitro by the maturation endopeptidase even in the presence of an excess of nickel ions. Evidence is presented that zinc does not interfere with the incorporation of iron into the metal center. Precursor of the large subunit accumulated in nickel proficient cells formed a transient substrate complex with the cognate endoprotease HycI whereas that of zinc-supplemented cells did not. The results show that zinc can intrude the nickel-dependent maturation pathway only when nickel uptake is blocked. Under this condition zinc appears to be incorporated at the nickel site of the large subunit and delivers a precursor not amenable to proteolytic processing since the interaction with the endoprotease is blocked.     

Cadmium and Nickel Toxicity for <Emphasis Type="Italic">Sinapis alba</Emphasis> Plants Inoculated with Endophytic Strains of <Emphasis Type="Italic">Bacillus subtilis</Emphasis>

We studied the effect of cadmium and nickel on Sinapis alba L. plants inoculated with endophytic strains of Bacillus subtilis. It was shown that treatment of S. alba seeds with endophytic strains of bacteria B. subtilis improves plant resistance to the toxic effect of cadmium and nickel and reduces manifestation of oxidative stress in the presence of higher levels of metal ions in the above-ground part of plants. Anti-stress effect and the ability of endophytic strains of B. subtilis to intensify uptake of cadmium and nickel ions by S. alba plants may be used for phytoextraction of heavy metals and stimulation of plant growth in contaminated areas.     

Characteristics of Phytogeochemistry in Copper Mine Area of Hongtou Shan,Liaoning Province

The contents of copper, zinc, lead nickel and cadmium for 322 samples of 44 species growing on copper mine area of Hongtou Shoo were determined. The results showed that the average contents of zinc, nickel, lead, cadmium in dry matter are 51.313 ppm, 1.536 ppm, 0.361 ppm and 0.058 ppm respectively. The variable range of zinc and cad- mium contents is larger, difference between minimum and maximum value is about 30–40 times. Zinc, lead and nickel contents in leaves of xylophyta in dry matter are mostly higher than in branches, but cadmium content of branches in dry matter is higher than leaves. The contents of lead and zinc in plants of minerelization areas are higher than that in non-minerelization areas. The results of correlative analysis showed that the linear regression between the metal contents in plants and soils are significant, for example, Lespedeza bicolor Thalictrum thumbergii, Arundinella hirta et al. It is important in phytogeochemical methods of prospecting for mineral. However, the correlative coefficients between the elements contents in leaves and branches of Quercus liaotungensis and in soils are not obvious. The correlative coefficient of nickel in plants and zinc, lead, cadmium and organic matter contents in soils are mostly negative value, without significant correlation. The results of the principal component analysis showed that the correlation of cadmium and zinc is significant among five elements in the plants. The contributive rate of first principal component is 33.94%, the positive target of the main target constitute is cadmium and zinc.     

Rhizobacteria of Populus euphratica Promoting Plant Growth Against Heavy Metals

The heavy metal-resistant bacteria from rhizospheric soils of wild Populus euphratica forest growing in arid and saline area of northwestern China were investigated by cultivation-dependent methods. After screening on medium sparked with zinc, copper, nickel and lead, 146 bacteria strains with different morphology were isolated and most of them were found to be resistant to at least two kinds of heavy metals. Significant increase in fresh weight and leaf surface area of Arabidopsis thaliana seedlings under metal stress were noticed after inoculated with strains especially those having multiple-resistance to heavy metals such as Phyllobacterium sp. strain C65. Investigation on relationship between auxin production and exogenous zinc concentration revealed that Phyllobacterium sp. strain C65 produced auxin, and production decreased as the concentration of zinc in medium increased. For wheat seedlings treated with zinc of 2 mM, zinc contents in roots of inoculated plants decreased by 27% (P < 0.05) compared to the uninoculated control. Meanwhile, zinc accumulation in the above-ground tissues increased by 22% (P < 0.05). The translocation of zinc from root to above-ground tissues induced by Phyllobacterium sp. strain C65 helped host plants extract zinc from contaminated environments more efficiently thus alleviated the growth inhibition caused by heavy metals.     

Phytochelatins as biomarkers for heavy metal stress in maize (Zea mays L.) and wheat (Triticum aestivum L.): combined effects of copper and cadmium

Heavy metal contaminated soils often show increased levels of more than one metal, e.g. copper (Cu), cadmium (Cd), zinc (Zn), lead (Pb) or nickel (Ni). In case such soils are used for crop production, prediction of yield reduction or quality decline due to heavy metals in the soil is inadequate when based only on chemical soil analysis. The use of biomarkers such as phytochelatins (PC), non-protein thiols specifically induced in plants upon exposure to heavy metals, may be an additional tool or diagnostic criterion in heavy metal research and in practice. In the present work, Cu and Cd uptake and induction of PC synthesis are studied with hydroponically grown maize and wheat plants exposed to mixtures of the two metals. We observed a close positive relationship between the concentrations of Cd and PC in the plant shoot material. A decreased shoot concentration of Cd after addition of Cu, due to metal competition at common root absorption sites, coincided with lower shoot PC levels. Also differences in metal uptake and xylary metal transport among the two plant species were reflected in corresponding differences in PC concentration. The observed direct relationship between shoot PC concentration and the degree of metal-induced growth inhibition makes the use of PC promising for the purpose tested for.     

单一与复合污染条件下两种敏感性植物对Cd、Zn、Pb的吸收效应

为了进一步研究镉、锌、铅 3种重金属元素间的相互作用以及对植物吸收重金属能力的影响 ,在模拟单一重金属污染试验研究的基础上 ,采用正交回归设计方案 ,研究了 Cd、Zn、Pb复合污染情况下紫花苜蓿和披碱草两种敏感性植物对 3种重金属的吸收效应。结果表明 ,在单一污染条件下 ,镉元素对紫花苜蓿生长的影响大于锌、铅 ,铅元素对披碱草生长的影响大于锌、镉 ;紫花苜蓿对于镉的吸收累积显著高于披碱草 ,植物内镉元素浓度最高达到 1 0 88.5 mg/kg,而披碱草对于铅元素的吸收则高于紫花苜蓿 ,植物内铅元素浓度最高达到 1 3 4 5 .5 mg/kg。在复合污染条件下 ,两种植物对铅、锌和铅、镉的吸收在不同浓度范围内分别存在存在着协同效应和拮抗效应 ;同时两种植物对锌、镉元素在实验涉及浓度范围内都存在着拮抗效应。这对于深入研究复合污染条件下重金属的土壤环境化学行为 ,对植物的综合毒性以及不同植物对重金属的吸收累积效应等 ,具有一定的参考意义     

Xanthan is not essential for pathogenicity in citrus canker but contributes to<Emphasis Type="Italic"> Xanthomonas</Emphasis> epiphytic survival

Xanthan-deficient mutants of Xanthomonas axonopodis pv. citri, the bacterium responsible for citrus canker, were generated by deletion and marker exchange of the region encoding the carboxy-terminal end of the first glycosyltransferase, GumD. Mutants of gumD did not produce xanthan and remained pathogenic in citrus plants to the same extent as wild-type bacteria. The kinetics of appearance of initial symptoms, areas of plant material affected, and growth of bacteria inside plant tissue throughout the disease process were similar for both wild-type and mutant inoculations. Moreover, exopolysaccharide deficiency did not impair the ability of the bacteria to induce hypersensitive response on non-host plants. Apart from variations in phenotypic aspects, no differences in growth or survival under different stress conditions were observed between the xanthan-deficient mutant and wild-type bacteria. However, gumD mutants displayed impaired survival under oxidative stress during stationary phase as well as impaired epiphytic survival on citrus leaves. Our results suggest that xanthan does not play an essential role in citrus canker at the initial stages of infection or in the incompatible interactions between X. axonopodis pv. citri and non-host plants, but facilitates the maintenance of bacteria on the host plant, possibly improving the efficiency of colonization of distant tissue.