Potential use of endophytic root bacteria and host plants to degrade hydrocarbons

Abstract

Microbe-assisted phytoremediation depends on competent root-associated microorganisms that enhance remediation efficiency of organic compounds. Endophytic bacteria are a key element of the root microbiome and may assist plant degradation of contaminants. The aim of this study was to investigate the application of four hydrocarbon-degrading endophytic strains previously isolated from an oil sands reclamation area. Strains EA1-17 (Stenotrophomonas sp.), EA2-30 (Flavobacterium sp.), EA4-40 (Pantoea sp.), and EA6-5 (Pseudomonas sp.) were inoculated in white sweet clover growing on soils amended with diesel at 5,000, 10,000, and 20,000?mg·kg^?1. Our results indicate that plant growth inhibition caused by diesel fuel toxicity was overcome in inoculated plants, which showed significantly higher plant biomass. Analysis of soil F2 and F3 hydrocarbon fractions also revealed that these soils were remediated by inoculated plants when diesel was applied at 10,000?mg·kg^?1 and 20,000?mg·kg^?1. In addition, quantification of hydrocarbon-degrading genes suggests that all bacterial strains successfully colonized sweet clover plants. Overall, the endophytic strain EA6-5 (Pseudomonas sp.), which harbored hydrocarbon-degrading genes, was the most effective candidate in phytoremediation experiments and could be a strategy to increase plant tolerance and hydrocarbon degradation in contaminated (e.g., diesel fuel) soils.     

Endophytic Bacteria Induce Growth Promotion and Wilt Disease Suppression in Oilseed Rape and Tomato

To determine whether bacteria isolated from within plant tissue can have plant growth-promotion potential and provide biological control against soilborne diseases, seeds and young plants of oilseed rape (Brassica napus L. cv. Casino) and tomato (Lycopersicon lycopersicum L. cv. Dansk export) were inoculated with individual bacterial isolates or mixtures of bacteria that originated from symptomless oilseed rape, wild and cultivated. They were isolated after surface sterilization of living roots and stems. The effects of these isolates on plant growth and soilborne diseases for oilseed rape and tomato were evaluated in greenhouse experiments. We found isolates that not only significantly improved seed germination, seedling length, and plant growth of oilseed rape and tomato but also, when used for seed treatment, significantly reduced disease symptoms caused by their vascular wilt pathogens Verticillium dahliae Kleb and Fusarium oxysporum f. sp. lycopersici (Sacc.), respectively.     

Infection Biology of Bacterial Wilt of Forage Grasses

Infection of perennial ryegrass (Lolium perenne L.), Italian ryegrass (Loliummultiflorum L.), and timothy (Phleum pratense L.) by Xanthomonas campestris pv. graminis and Xanthomonas campestris pv. phlei occurred mainly via wounds rather than natural openings. Nevertheless, bacteria were detected by isolation and immunofluorescence in plants sprayed with the pathogen without prior wounding and in plants in which intact ears had been dipped in inocula. High concentrations of bacteria were observed around the stomata of perennial ryegrass and timothy by scanning electron microscopy 48 h after inoculation. Perennial ryegrass and Italian ryegrass and individual plants of ryegrass and timothy differedin susceptibility to the pathogens.     

Phytoremediation of Oil-Sludge–Contaminated Soil

The aim of this research was to select plant species that could be effective in the phytoremediation of a former oil-sludge pit. Seven crop plants (Triticum aestivum L., Secale cereale L., Avena sativa L., Hordeum vulgare, Sorghum bicolor L. Moench, Panicum miliaceum L., and Zea mays L.), five wild grasses (Lolium perenne L., Bromopsis inermis, Agropyron cristatum L., Agropyrum tenerum L., and Festuca pratensis Huds.), and three legumes (Medicago sativa L., Trifolium pratense L., and Onobrychis antasiatica Khin.) were screened for phytotoxicity, including the assessment of germination, shoot biomass, and root biomass, in a pot experiment. The estimation of oil-sludge degradation in the root zone of the tested plants showed that rye accelerated cleanup most effectively, degrading all of the main contaminant fractions in the oil sludge by a total of 52%. Although alfalfa had a lower phytoremediation potential than did rye, it maintained large numbers of soil microorganisms, including polycyclic aromatic hydrocarbon degraders, in its rhizosphere. Rye and alfalfa were chosen for a large-scale study to remediate an oil-sludge pit on the grounds of a petroleum refinery. Remediation monitoring confirmed the effectiveness of rye: the oil-sludge content decreased consistently for 3 years and remained low in comparison with the results from other plant species.     

Polymorphism of lectin genes in <Emphasis Type="Italic">Lathyrus</Emphasis> plants

The carbohydrate-binding sequences of the lectin genes from spring vetchling Lathyrus vernus (L.) Bernh., marsh vetchling L. palustris (L.), and Gmelin’s vetchling L. gmelinii (Fitsch) (Fabaceae) were determined. Computer-aided analysis revealed substantial differences between nucleotide and predicted amino acid sequences of the lectin gene regions examined in each of the three vetchling species tested. In the phylogenetic trees based on sequence similarity of carbohydrate-biding regions of legume lectins, the sequences examined formed a compact cluster with the lectin genes of the plants belonging to the tribe Fabeae. In each plant, L. vernus, L. palustris, and L. gmelinii, three different lectin-encoding genes were detected. Most of the substitutions were identified within the gene sequence responsible for coding the carbohydrate-binding protein regions. This finding may explain different affinity of these lectins to different carbohydrates, and as a consequence, can affect the plant host specificity upon development of symbiosis with rhizobium bacteria.     

Use of integrated phytoremediation for cleaning-up of oil-sludge-contaminated soil

The possibility of using multicomponent systems, including plants, mineral fertilizers, and plant growth promoting microorganisms, has been studied in vegetative experiments in order to stimulate phytoremediation of oil-sludge-contaminated soil. Winter rye (Secale cereale L.) was used as the principal phytoremediating plant species, whereas alfalfa (Medicago sativa L.), nitrogen fertilizer (ammonium nitrate), and a PGPR strain (Azospirillum brasilense SR80) were applied as additional components, individually or in various combinations. The obtained data revealed the critical importance of alfalfa for phytoremediation of hydrocarbon-contaminated soil. Application of different multicomponent treatments resulted in approximately 70% reduction of pollutant concentration in soil. The developed technological approaches were successfully tested in the remediation of an ex-oil-sludge pit on the ground of a petroleum refinery.     

Rhizosphere bacteria enhance the accumulation of selenium and mercury in wetland plants

The role of rhizosphere bacteria in facilitating Se and Hg accumulation in two wetland plants, saltmarsh bulrush (Scirpus robustus Pursh) and rabbitfoot grass (Polypogon monspeliensis (L.) Desf.), was studied. Ampicillin-amended plants (i.e., with inhibited rhizosphere bacteria) supplied with Na₂SeO₄ or HgCl₂ had significantly lower concentrations of Se and Hg, respectively, in roots than plants without ampicillin. These results were confirmed by inoculating axenic saltmarsh bulrush plants with bacteria isolated from the rhizosphere of plants collected from the field; these plants accumulated significantly more Se and Hg compared to axenic controls. Therefore, rhizosphere bacteria can increase the efficiency of Se and Hg phytoremediation by promoting the accumulation of Se and Hg in tissues of wetland plants. Received: 9 April 1999 / Accepted: 11 May 1999     

Evidence for a general light-dependent negative control of NADPH-protochlorophyllide oxidoreductase in angiosperms

The effect of light on NADPH-protochlorophyllide oxidoreductase and its mRNA has been studied in five different species of dicotyledonous plants, bean (Phaseolus vulgaris L.), pea (Pisum sativum L.), tomato (Lycopersicon esculentum Mill.), sunflower (Helianthus annuns L.) and mustard (Sinapis alba L.), and in two monocotyledonous plant species, maize (Zea mays L.) and barley (Hordeum vulgare L.). In all these species, illumination of etiolated seedlings led to a rapid decline of both the activity and the content of the enzyme protein. These results indicate that there may be a general light-dependent regulation of the enzyme common to higher plants.Abbreviation Pchlide reductase NADPH-protochlorophyllide oxidoreductase Didicated to Professor H. Mohr on the occasion of his 60th birthdayWe are grateful to P. Westhoff and H. Schrubar (Botanisches Institut, Universität Düsseldorf, FRG) for making available to us their data on the Pchlide reductase of Sorghum bicolor prior to publication and for sending us seeds of this plant species. This work has been supported by the Deutsche Forschungsgemeinschaft.     

UV‐B impact on aphid performance mediated by plant quality and plant changes induced by aphids

Plants face various abiotic and biotic environmental factors and therefore need to adjust their phenotypic traits on several levels. UV‐B radiation is believed to impact herbivorous insects via host plant changes. Plant responses to abiotic challenges (UV‐B radiation) and their interaction with two aphid species were explored in a multifactor approach. Broccoli plants [Brassica oleracea L. convar. botrytis (L.), Brassicaceae] were grown in two differently covered greenhouses, transmitting either 80% (high UV‐B) or 4% (low UV‐B) of ambient UV‐B. Three‐week‐old plants were infested with either specialist cabbage aphids [Brevicoryne brassicae (L.), Sternorrhyncha, Aphididae] or generalist green peach aphids [Myzus persicae (Sulzer), Sternorrhyncha, Aphididae]. Plants grown under high‐UV‐B intensities were smaller and had higher flavonoid concentrations. Furthermore, these plants had reduced cuticular wax coverage, whereas amino acid concentrations of the phloem sap were little influenced by different UV‐B intensities. Cabbage aphids reproduced less on plants grown under high UV‐B than on plants grown under low UV‐B, whereas reproduction of green peach aphids in both plant light sources was equally poor. These results are likely related to the different specialisation‐dependent sensitivities of the two species. The aphids also affected plant chemistry. High numbers of cabbage aphid progeny on low‐UV‐B plants led to decreased indolyl glucosinolate concentrations. The induced change in these glucosinolates may depend on an infestation threshold. UV‐B radiation considerably impacts plant traits and subsequently affects specialist phloem‐feeding aphids, whereas aphid growth forces broccoli to generate specific defence responses.     

Comparative Characteristics of Carbohydrate Binding by Lectins from Broad Bean,Pea, Common Vetch,and Lentil Seeds

Lectins from the seeds of broad bean (Vicia faba L.), pea (Pisum sativum L.), common vetch (V. sativa L.), and lentil (Lens culinaris Medik.) were isolated and purified by affinity chromatography. The hemagglutinating activity of lectins was most effectively inhibited by methyl--D-mannopyranoside, trehalose, and D-mannose. Other carbohydrate haptens, such as methyl--D-glucopyranoside, maltose, and alginic and D-glucuronic acids were less effective. Two lectins obtained from different lentil cultivars, unlike other lectins, had a relatively high affinity for melecitose, N-acetyl-D-glucosamine, L-sorbose, and sucrose. Furthermore, these lectins interacted with soluble starch. All the lectins examined had similar, but not identical, carbohydrate-binding properties. Because of their similar D-mannose/D-glucose specificity, these lectins interacted with lipopolysaccharides and exopolysaccharides of Rhizobium leguminosarum bv. viciae, root nodule bacteria that infect broad-bean, pea, common-vetch, and lentil plants with the formation of nitrogen-fixing symbiosis. However, owing to individual distinctions of carbohydrate-binding properties, these lectins showed a higher affinity for the polysaccharides of those microsymbionts within the R. leguminosarum bv. viciae species that were better specialized towards one or the other host plant from the cross inoculation group of legumes.     

Effect and Aftereffect of Temperature on Respiration of Intact Plants

Effects and aftereffects of typical temperatures of cultivar habitat (background temperature), heat-hardening, and cold-hardening temperatures on dark respiration of leaf segments and intact plants were investigated on plant species differing in cold tolerance—cucumber (Cucumis sativus L.), tomato (Lycopersicon esculentum Mill.), cicer milkvetch (Astragalus cicer L.), and narrow-leaved lupine (Lupinus angustifolium L.). At cold-hardening temperatures, the respiratory metabolism underwent rearrangements serving to compensate for elevated energy losses during plant adaptation. This was manifested in the increase in the respiratory coefficient (RC) and the Q ₁₀ coefficient during hardening. The preconditioning of plants at hardening temperatures enhanced O₂ uptake and elevated the ratio of growth respiration to maintenance respiration in the post-treatment period. Conversely, temperature variations within the background range had no aftereffect on RC, Q ₁₀, and O₂ uptake.     

Contribution of Oxidative Stress to the Development of Cold-Induced Damage to Leaves of Chilling-Sensitive Plants: 2. The Activity of Antioxidant Enzymes during Plant Chilling

Changes in the activities of cytosolic superoxide dismutase, ascorbate peroxidase, and catalase were studied in 7–11-day-old seedlings of maize (Zea mays L.), cucumber (Cucumis sativus L.), millet (Panicum miliaceum L.), and etiolated potato (Solanum tuberosum L.) sprouts. The assays were performed immediately after chilling at 2°C for 1–24 h and one day after 24-h chilling. During the first 1–2 h of chilling, enzyme activities were substantially reduced in chilling-sensitive plants (cucumber and maize). Further chilling resulted in a gradual increase in the enzyme activities to a degree dependent on plant species. One day after the plants were returned to a high temperature, the enzyme activities were restored to an initial level or exceeded it (excluding maize superoxide dismutase). In the potato (cold-resistant species), we did not observe any regular changes in the activities of antioxidant enzymes. On the whole, the activities of these enzymes inversely depended on species cold-resistance. The conclusion is that one of the cold-resistance factors is the capacity of antioxidant enzymes to maintain their activities during chilling and restore them relatively rapidly after plant transfer to warm conditions.     

Testing the efficiency of three 15N-labeled nitrogen compounds for indirect labeling of grasshoppers via plants in the field

In field studies of plant–insect herbivore interactions it is often difficult to establish which herbivore has fed on a particular plant. We investigated the suitability of three different ¹⁵N‐labeled nitrogen compounds (ammonium, nitrate, and glycine) for indirect marking of three grasshopper species [Omocestus viridulus (L.), Chorthippus parallelus (Zett.), and Chorthippus biguttulus (L.) (Orthoptera: Acrididae)] through labeling their food plants in the field. In two short‐term experiments grassland plots of 1 m² were separately labeled with either one of the different nitrogen compounds. Grasshoppers were caged on three food‐plant species [Dactylis glomerata L., Holcus lanatus L. (Poaceae), and Trifolium repens L. (Fabaceae)] present in these plots for 72 h. Significantly enriched δ¹⁵N values in grasshoppers were found in all plant/grasshopper combinations. Enrichment in grasshoppers was positively correlated with the enrichment of plants and labeling with nitrate resulted in highest ¹⁵N enrichment. In a long‐term experiment, individuals of C. biguttulus were placed in a cage covering an area of 1 m² for 37 days, with sampling of grasshoppers at regular intervals. δ¹⁵N values of the grasshopper and a common food plant, D. glomerata, increased steadily over time, up to 40‐fold by the end of the experiment. Our results demonstrate that ¹⁵N‐labeling of plants is an appropriate tool for the investigation of insect–plant interactions under natural conditions.     

Relative preference of Lygus hesperus (Hemiptera: Miridae) to selected host plants in the field

Abstract Information on host plant preference of agriculturally important insect pests, such as Lygus hesperus (Knight), can be helpful in predicting its occurrence and future movement among crop and non-crop host plants. A field study was conducted during 2005 and 2006 to evaluate the host preference of Lygus to cotton and four other host plants in the Texas High Plains, including alfalfa (Medicago sativa L.), wild sunflower (Helianthus annuus L.), Russian thistle (Salsola iberica L.) and pigweed (Amaranthus palmeri L.). Sampling for both nymphs and adults during 2005 (July to November) and 2006 (June to November) showed that alfalfa and Russian thistle were the two most preferred hosts out of the five hosts evaluated. Abundance of nymphs (numbers per 50 sweeps per host plant) during the sampling period also indicated the superior reproductive suitability of alfalfa and Russian thistle. Cotton appeared to be the least attractive host plant for Lygus when Russian thistle and alfalfa were available in the host mosaic. Seasonal abundance of Lygus was found to be lower during 2006 compared to 2005, which may be explained by the difference in rainfall patterns during these two years. In terms of species dominance, L. hesperus was the most dominant species in the sampled population followed by an inconsiderable fraction of L. elisus and L. lineolaris.     

Response of the pollen beetle Meligethes aeneus to volatiles emitted by intact plants and conspecifics

The response of the pollen beetle Meligethes aeneus Fab. (Coleoptera, Nitidulidae) to the volatiles of undamaged plants and conspecifics was tested in a Y-tube-olfactometer-bioassay. Beetles that had hibernated preferred significantly the volatiles emitted by their most important host plant, oilseed-rape (Brassica napus L. ‘Lorar’) in the early bud-stage. However, the odour emitted by rye (Secale cereale L.), tomato plants (Solanum lycopersicum L.), and yarrow (Achillea millefolium L.) were also attractive when tested against the corresponding growing-medium. Dock plants (Rumex obtusifolius L.) and touch-me-not (Impatiens parviflora L.) possessed no attractive properties. When tested against each other, oilseed-rape was preferred significantly by M. aeneus above all other plants, with the exception of tomato. The results indicate that M. aeneus is able to locate its host plant by olfactory stimuli in the early bud-stage, i.e. in that stage in which the infestation begins in the field and when the typical yellow colour and floral scent of oilseed-rape are absent. Female pollen beetles avoided significantly the volatiles emitted by female conspecifics and an ether extract of conspecifics of mixed sex, while volatiles from males had no significant effect on females. Furthermore, males showed no preferences when responding to conspecific odour in the olfactometer. These results suggest the existence of an epideictic pheromone for M. aeneus.     

Effect of the saprophytic fungus Fusarium oxysporum on arbuscular mycorrhizal colonization and growth of plants in greenhouse and field trials

Effects of the saprophytic fungus Fusarium oxysporum on arbuscular mycorrhizal (AM) colonization and plant dry matter were studied in greenhouse and field experiments. Host plants: maize (Zea mays L.), sorghum (Sorghum vulgare L.), lettuce (Lactuca sativa L.), tomato (Lycopersicum esculentum L.), wheat (Triticum vulgare L), lentil (Ervum lens L.) and pea (Pisum sativum L.), the AM fungi: Glomus mosseae, G. fasciculatum, G. intraradices, G. clarum, and G. deserticola and the carriers for F. oxysporum inoculum: aqueous solution, thin agar slices, and pellets of agar and alginate were tested under greenhouse conditions. Greatest plant growth and AM colonization responses in sterilized and unsterilized soils were observed with pea, Glomus deserticola and sodium alginate pellets as the carrier for F. oxysporum inoculum. Under field conditions, adding F. oxysporum increased the survival of transplanted pea, possibly through a beneficial effect on AM fungi. Application of F. oxysporum increased shoot dry matter, N and P concentrations of pea and sorghum plants, and the level of AM colonization attained by indigenous or introduced AM fungi. These parameters were similar in plants inoculated with either G. deserticola or with the indigenous AM fungi. Application of the saprophytic fungus increased the number of propagules of AM fungi in field plots in which pea was grown, but this increase was not sufficient to increase AM colonization of sorghum after the pea crop. This revised version was published online in June 2006 with corrections to the Cover Date.     

Influence of the food plants on the degree of parasitism of larvae ofHeliothis armigera byCotesia kazak

Influence of the food plants ofHeliothis armigera (Hb.) on the degree of parasitism by exotic parasiteCotesia kazak Telenga (Hymenoptera: Braconidae) was studied in cages in the laboratory on 7 food plants such as cotton (Gossypium hirsutum L.), tomato (Lycopersicon esculentum Mill), okra [Abelmoschus esculentus (L.) Moench], Dolichos (dolichos lablab L.), pigeonpea [Cajanus cajan (L.) Millsp.], Cowpea (Vigna unquiculata (L.) and chickpea (Cicer arietium L.). To determine the preference of the parasite 2 test methods were employed. In single plant choice test cotton was most preferred. Next in order of preference were tomato and okra. Dolichos, pigeonpea, cowpea and chickpea were least preferred. In multiple choice test, however, cotton and okra were preferred followed by tomato. Parasites were seen visiting these plants very frequently and high parasitism was recorded on these plants. Chick pea, pigeon pea, cowpea and Dolichos were the least preferred food plants. There appears to be some difference in fecundity as affected by some food plants. Exposure on okra, cotton and tomato resulted in higher cocoon production as compared to pigeonpea, Dolichos, cowpea and chickpea. There was, however, no difference in sex-ratio and longevity of the progeny as affected by food plants. This exotic parasite should be released first in crops such as cotton, okra and tomato on whichH. armigera is a very serious pest in India and elsewhere. Contribution No. 140/86 of the Indian institute of Horticultural Research, Bangalore-560 089     

Genetic transformation of perennial tropical fruits

Summary Genetic transformation provides the means for modifying single horticultural traits in perennial plant cultivars without altering their phenotype. This capability is particularly valuable for perennial plants and tree species in which development of new cultivars is often hampered by their long generation time, high levels of heterozygosity, nucellar embryony, etc. Most of these conditions apply to many tropical and subtropical fruit crops. Targeting specific gene traits is predicated upon the ability to regenerate elite selections of what are generally trees from cell and tissue cultures. The integrity of the clone would thereby remain unchanged except for the altered trait. This review provides an overview of the genetic transformation of perennial tropical and subtropical fruit crops, i.e., citrus (Citrus spp.), banana and plantain (Musa groups AAA, AAB, ABB, etc.), mango (Mangifera indica L.), pineapple (Ananas comosus L.), avocado (Persea americana Mill.), passion fruit (Passiflora edulis L.), longan (Dimocarpus longan Lour.), and litchi (Litchi chinensis Sonn.).     

The influence of colonizing methylobacteria on morphogenesis and resistance of sugar beet and white cabbage plants to <Emphasis Type="Italic">Erwinia carotovora</Emphasis>

The influence of colonization of sugar beet (Beta vulgaris var. saccharifera (Alef) Krass) and white cabbage (Brassica oleracea var. capitata L.) plants by methylotrophic bacteria Methylovorus mays on the growth, rooting, and plant resistance to phytopathogen bacteria Erwinia carotovora was investigated. The colonization by methylobacteria led to their steady association with the plants which had increased growth speed, root formation and photosynthetic activity. The colonized plants had increased resistance to Erwinia carotovora phytopathogen and were better adapted to greenhouse conditions. The obtained results showed the perspectives for the practical implementation of methylobacteria in the ecologically clean microbiology substances used as the plant growth stimulators and for the plant protection from pathogens.     

Free-living culturable bacteria and protozoa from the rhizoplanes of three floating aquatic plant species

Terrestrial plant roots exude compounds that promote the proliferation of microorganisms, a phenomenon called the rhizosphere effect. However, little is known about the influence of roots of aquatic plants on microbial populations. We compared cultivable bacteria and protozoa from the rhizoplanes of Azolla filiculoides Lam., Lemna gibba L., and Ricciocarpus natans L., collected at the Tecocomulco Lagoon (Hidalgo, Mexico). The functional bacterial groups isolated from A. filiculoides, L. gibba and R. natans, were macro- and microscopically characterized, and phylogenetically identified using the 16S rDNA gen. About 96% of isolates corresponded to Gram-negative bacteria, and potential N-fixing free-living bacteria (diazotrophic bacteria) were the most abundant. Molecular analysis detected 15 bacterial genera in the rhizoplane of R. natans, whereas A. filiculoides and L. gibba only yielded five genera, among which Aeromonas was predominant. Twenty-five genera of flagellated and 20 genera of ciliated protozoa were identified. Bodo was the more abundant flagellated, whereas Halteria was the most frequent ciliate. All three aquatic plants showed the rhizospheric effects. The most abundant and diverse community of protozoa was found in A. filiculoides, which also had the most abundant bacterial community, but the highest bacterial diversity was found in R. natans.