1,720,971 research outputs found
Comparison between cultivated and total bacterial communities associated with Cucurbita pepo using cultivation-dependent techniques and 454 pyrosequencing.
No full textEndophytic bacteria often have beneficial effects on their host plants that can be exploited for bioremediation applications but, according to the literature, only 0.001–1% of all endophytic microbes should be cultivable. This study compared the cultivated endophytic communities of the roots and shoots of Cucurbita
pepo with the total endophytic communities as determined by cultivation-dependent techniques and 454 pyrosequencing. The ten most abundant taxa of the total communities aligned well with the
cultivated taxa; however, the abundance of these taxa in the two communities differed greatly. Enterobacter showed very low presence in the total communities, whereas they were dominantly present in the cultivated communities. Although Rhizobium dominated in total root and shoot communities, it was poorly cultivable and even then only in growth media containing plant extract. Since endophytes likely contribute to plant-growth promotion, cultivated bacterial strains were tested for their plant-growth promoting capabilities, and the results were correlated with their abundance in the total community. Bacillus and Pseudomonas showed promising results when considering cultivability, abundance in the total community and plant-growth promoting capability. This study demonstrated that, although a limited number of bacterial genera were cultivable, current
cultivation-dependent techniques may be sufficient for further isolation and inoculation experiments that aim to improve phytoremediation efficiency
The role of endophytes and copper nanoparticles in the success or failure of DDE phytoremediation using Cucurbita pepo
No full text2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane (DDT) was produced and applied as a pesticide starting in 1939, and was used globally by 1943 (Turusov et al., 2002). In 1974, sufficient evidence was gathered demonstrating that DDT and its metabolites, 2,2-bis(p-chlorophenyl)-1,1-dichloro-ethylene (DDE) and 1,1- dichloro-2,2-bis(p-chlorophenyl)-ethane (DDD), were persistent in the environment and showed bioaccumulation in higher animal species causing for instance egg shell thinning and endocrine disruption as a consequence (Thomas et al., 2008). These findings lead to the ban of the production and use in Belgium. DDE toxicity and recalcitrance are therefore regarded as important environmental problems. The hydrophobic character of DDE causes a strong adsorption to soil particulates, making it difficult to remove it from soils. The research of White et al. (2010) has demonstrated that Cucurbita pepo ssp. pepo cultivar Raven (Zucchini Raven) has a strong potential to extract and translocate weathered DDE from soils. The main objective of this research was to improve phytoremediation of DDE-contaminated soils with Cucurbita pepo through the use of plant-associated bacteria and copper nanoparticles. To utilize plant growth-promoting endophytes in phytoremediation applications, it is necessary that they are cultivable in laboratory conditions. Therefore, we investigated different media and gelling agents as well as the effect of the addition of plant extract to the medium on cultivability of endophytic strains. For these purposes, the bacterial communities were identified using both cultivationdependent and cultivation-independent methods and their possible plant growthpromoting capacities were investigated. In our research, a 1/10 diluted rich 869 medium proved to yield the highest numbers of endophytes as well as the highest diversity. Furthermore, we also investigated whether adding plant extract to the bacterial growth medium enhanced the growth of bacteria that were previously stored at -80°C and had lost their ability to grow. The addition of plant extract indeed lead to a significant increase in the growth capacity of bacterial strains that were stored in glycerol. A next step in our research was to evaluate the effects of DDE on both the cultivable and total endophytic communities. We observed an increased endophytic diversity in plants that were exposed to DDE and identified several bacterial strains that could resist DDE toxicity such as Sphingomonas sp. and Stenotrophomonas sp. Recently, copper nanoparticles (CuNPs) are added to pesticides for their antifungal ability as well as their capacity to increase the uptake of pesticides into the plants. Therefore, the effects of CuNPs on plant growth, endophytic communities and DDE uptake were evaluated. Some bacterial strains showed to be sensitive to the combination of DDE and CuNPs, while others showed enhanced presence in the endophytic communities. Ten strains exhibiting both DDE-degrading and plant growth-promoting capacities were selected for a further investigation of their possible application in DDE phytoremediation. Of the 10 strains that were tested, 3 showed a good inoculation efficiency and plant growth-promoting capacity. Therefore, these three strains were selected for a DDE-degradation experiment using GCMS analysis. All three strains demonstrated a good ability to degrade DDE when inoculated in selective 284 medium supplemented with DDE. The genomes of these strains were also fully sequenced which showed them to be Sphingomonas taxi UH1, Methylobacterium radiotolerans UH1 and Enterobacter aerogenes UH1. By analyzing the genomes, several genes involved in plant growth-promotion and DDE-degradation were identified. After investigating the effects of DDE, CuNPs and endophytes separately, the combined effects of these factors on Cucurbita pepo and its DDE-uptake were evaluated. For this experiment, plants were inoculated with S. taxi UH1, M. radiotolerans UH1, E. aerogenes UH1, or a consortium of all three strains before being exposed to CuNPs and DDE. The effects on the plant growth, as well as the changes in DDE-uptake were studied. The presence of CuNPs caused a decrease of plant weight. Inoculation with the selected endophytes however, increased the plant weights to be higher than the non-inoculated control plants. The DDE concentrations of the plants exposed to CuNPs were significantly higher than those of non-exposed plants. The final experiment was to verify if the knowledge that was obtained during all previous experiments in the laboratory could be applied under field conditions. Plants were inoculated with the bacterial strains and grown for 100 days in a DDE-contaminated field. The effects of the inoculation and DDE-contamination were evaluated on both the plants and their endophytic communities (cultivable and total). The results showed a significant increase of the amount of DDE that was extracted from the soil by plants that were inoculated with the consortium of Enterobacter aerogenes UH1, Methylobacterium radiotolerans UH1, and Sphingomonas taxi UH1 in comparison to the non-inoculated control plants. Therefore, we can conclude that the phytoremediation of DDEcontaminated soils with Cucurbita pepo plants can be successfully enhanced through inoculation with DDE-degrading, plant growth promoting endophytes. In laboratory experiments, the presence of CuNPs demonstrated promising results towards increased uptake of DDE, but due to legislative constraints, the effects of CuNPs could not be evaluated in field conditions.2,2-bis(p-chlorofenyl)-1,1,1-trichloro-ethaan (DDT) werd geproduceerd en toegepast als pesticide vanaf 1939 en het gebruik ervan was tegen 1943 wereldwijd verspreid (Turusov et al., 2002). In 1974 waren er voldoende bewijzen dat DDT en zijn metabolieten, 2,2-bis(p-chlorofenyl)-1,1-dichloroethyleen (DDE) en 1,1-dichloro-2,2-bis(p-chlorofenyl)-ethaan (DDD), zeer persistent waren in het milieu en geaccumuleerd werden in de vetweefsels van hogere diersoorten met verdunning van eierschalen en endocriene verstoring als gevolg (Thomas et al., 2008), wat leidde tot verbieden van zowel het gebruik als de productie van DDT in België. DDE-toxiciteit en persistentie in het milieu worden hierdoor beschouwd als belangrijke milieuproblemen. Het hydrofobe karakter van DDE veroorzaakt een sterke absorptie aan bodempartikels waardoor het moeilijk verwijderbaar is uit de bodem. Het onderzoek van White et al. (2010) toonde het potentieel van Cucurbita pepo ssp. pepo cultivar Raven (Zucchini Raven) om verweerde DDE uit bodems te extraheren en binnen de plant te transporteren aan. De voornaamste doelstelling van dit onderzoek was om fytoremediatie van DDE-vervuilde bodems met Cucurbita pepo te verbeteren door middel van het gebruik van plant-geassocieerde bacteriën en kopernanopartikels (CuNPs). Om plantengroei-bevorderende bacteriën toe te passen in fytoremediatie is het noodzakelijk dat de bacteriën gegroeid kunnen worden in laboratoriumomstandigheden. Daarom werden verschillende media en stollingsmiddelen voor deze media getest, alsook het effect van het toevoegen van plantenextracten aan het bacterieel medium. Tijdens deze experimenten werden de bacteriële gemeenschappen geïdentificeerd door middel van cultivatie-afhankelijke en cultivatie-onafhankelijke methoden en werden hun plantengroei-bevorderende eigenschappen nagegaan. Ons onderzoek toonde aan dat een 1/10 verdund rijk 869 medium zowel de hoogste aantallen bacteriën opleverde, alsook de hoogste diversiteit aan endofyten. Verder werd onderzocht of de toevoeging van plantextract aan het medium kon leiden tot een verbeterde groei van bacteriële stammen waarvan de groeicapaciteit sterk afgenomen of zelfs verloren was na bewaring in een glyceroloplossing bij -80°C. De toevoeging van plantextract leidde inderdaad tot een significante toename van de groeicapaciteit van bacteriën die in een glycerolstock werden bewaard. Een volgende stap in het onderzoek was om de effecten van DDE op zowel de cultiveerbare als de totale endofytische gemeenschappen te evalueren aangezien dit de contaminant is waarop er gefocust werd. We stelden een toename vast van de diversiteit aan endofyten in planten die werden blootgesteld aan DDE en we identificeerden meerdere bacteriële stammen die een hoge tolerantie voor DDE vertoonden, zoals Sphingomonas sp. en Stenotrophomonas sp. Omwille van hun antifungale eigenschappen en om de opname van pesticiden in planten te verhogen worden sedert kort CuNPs toegevoegd aan pesticiden. Daarom hebben we de effecten van CuNPs op de groei van de plant, de endofytische gemeenschappen en de DDE-opname bestudeerd. Sommige bacteriële stammen werden duidelijk geïnhibeerd door de combinatie van DDE en CuNPs, terwijl anderen een verhoogde abundantie vertoonden in de endofytische gemeenschap. Tien bacteriële stammen die zowel DDEdegraderende als plantengroei-bevorderende eigenschappen vertoonden, werden geselecteerd voor verder onderzoek naar hun mogelijke toepassing in de fytoremediatie van DDE. Van de 10 stammen die getest werden, vertoonden er 3 een goede inoculatie-efficiëntie en bevordering van de groei van de planten. Deze 3 stammen werden daarom gekozen voor een DDE-afbraak-experiment gebruik makend van GCMS analyse. De 3 stammen konden DDE afbreken wanneer ze in een selectief 284 medium aangerijkt met DDE geïnoculeerd werden. De volledige genomen van deze stammen werden gesequeneerd. Dit toonde aan dat de stammen tot de soorten Sphingomonas taxi UH1, Methylobacterium radiotolerans UH1 en Enterobacter aerogenes UH1 behoren. Door analyse van de genomen konden verscheidene genen betrokken in de bevordering van de plantengroei en de afbraak van DDE geïdentificeerd worden. Nadat de effecten van DDE, CuNPs en endofyten apart werden bestudeerd, werden ook de gecombineerde effecten van deze factoren geëvalueerd. Tijdens dit experiment werden de planten geïnoculeerd met S. taxi UH1, M. radiotolerans UH1 en E. aerogenes UH1 of een consortium van de 3 stammen voordat ze werden blootgesteld aan CuNPs en DDE. De effecten op de plantengroei en de verschillen in DDE-opname werden geëvalueerd. De aanwezigheid van CuNPs veroorzaakte een afname in het gewicht van de planten. Wanneer de planten echter geïnoculeerd waren met de endofyten, nam het gewicht van de planten toe. In een finaal experiment werd de in het laboratorium vergaarde kennis getest onder veldcondities. Planten werden geïnoculeerd met de geselecteerde endofyten en gedurende 100 dagen gegroeid in een met DDE vervuild veld. De effecten van de inoculatie en de blootstelling aan DDE-vervuiling werden bestudeerd zowel op de groei van de planten als op de cultiveerbare en totale endofytische gemeenschappen. De resultaten toonden een significante toename in de hoeveelheid DDE die verwijderd werd uit de bodem door de planten geïnoculeerd met het consortium van Enterobacter aerogenes UH1, Sphingomonas taxi UH1 en Methylobacterium radiotolerans UH1 in vergelijking met de niet-geïnoculeerde controleplanten. We kunnen daardoor besluiten dat fytoremediatie van DDE-vervuilde bodem met Cucurbita pepo planten succesvol verbeterd kan worden door de inoculatie van planten met DDE-degraderende, plantengroei-bevorderende endofyten. Ook de toepassing van CuNPs toonde onder laboratoriumomstandigheden beloftevolle resultaten voor het verbeteren van fytoremediatie van DDE, maar dit kon door wettelijke beperkingen niet geëvalueerd worden onder veldcondities.Agentschap Innoveren & Onderneme
Optimization of DDE-phytoremediation by exploiting plant-associated bacteria and nanoparticles
No full textIntroduction Researchers at The Connecticut Agricultural Experiment Station observed a
remarkable difference in DDE accumulation at the subspecies level of Cucurbita pepo. C.
pepo ssp pepo accumulates DDE, while C. pepo ssp ovifera did not possess this capacity. In a
first part, this study investigates whether the the differences in DDE accumulation can be
related to differences in the plant-associated bacterial populations of the different subspecies .
Bacteria were isolated from both seeds and plants of accumulating and non-accumulating
Cucurbita pepo subspecies. The plants were exposed to 100 μg L-1 DDE.
The second part of this projects concentrates on silver nanoparticles (AgNPs) and their
capability to increase the uptake of organic contaminants by plants. Here, the possibility to
optimize DDE phytoremediation by exploiting both plant-associated bacteria as well as
AgNPs was investigated. Plants were exposed to 100 μg L-1 DDE, 500 mg L-1 AgNPs or both.
The effects of DDE and AgNPs on plant growth and on the associated bacterial populations
were investigated. Plant biomasses were determined and endophytes from both subspecies in
all conditions were isolated. All isolated bacteria were subjected to (1) genotypic
identification, (2) characterization of their plant growth promoting capacity, (3) screening for
AgNP toxicity and (4) screening for DDE degradation capacity.
Results DDE proved to have a toxic effect on plant growth, while AgNPs did not cause a
decrease in biomass. The effect on the total number of plant-associated bacteria that could be
isolated was the opposite. While DDE increased the number of endophytes in zucchini Raven,
exposure to AgNPs caused a severe decrease. Endophytes associated with zucchini Raven
demonstrated more plant growth promoting capacities than squash-associated bacteria.
Bacteria that were isolated from plants that were exposed to DDE or AgNPs showed to
experience less toxic effects when again exposed to these products.
Conclusion The DDE accumulator Zucchini Raven contains a higher number and diversity of
associated bacteria and its bacteria show more plant growth promoting capacity and potential
DDE degradation capacity than the bacteria associated with the non-DDE-accumulator squash
Zephyr. These findings and the higher DDE-uptake of zucchini Raven makes it a suitable
organism for DDE phytoremediation.
On one hand, AgNPs can be used to increase the DDE uptake of Cucurbita pepo, but on the
other hand it has severe toxic effects on the plant-associated bacteria. Therefore, a good
balance has to be discovered between the advantages and disadvantages of AgNPs for
bacteria-enhanced phytoremediation of DDE using Cucurbita pepo ssp. pepo
The role of endophytes and copper nanoparticles in the success or failure of DDE phytoremediation using Cucurbita pepo
No full text2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane (DDT) was produced and applied as a pesticide starting in 1939, and was used globally by 1943 (Turusov et al., 2002). In 1974, sufficient evidence was gathered demonstrating that DDT and its metabolites, 2,2-bis(p-chlorophenyl)-1,1-dichloro-ethylene (DDE) and 1,1- dichloro-2,2-bis(p-chlorophenyl)-ethane (DDD), were persistent in the environment and showed bioaccumulation in higher animal species causing for instance egg shell thinning and endocrine disruption as a consequence (Thomas et al., 2008). These findings lead to the ban of the production and use in Belgium. DDE toxicity and recalcitrance are therefore regarded as important environmental problems. The hydrophobic character of DDE causes a strong adsorption to soil particulates, making it difficult to remove it from soils. The research of White et al. (2010) has demonstrated that Cucurbita pepo ssp. pepo cultivar Raven (Zucchini Raven) has a strong potential to extract and translocate weathered DDE from soils. The main objective of this research was to improve phytoremediation of DDE-contaminated soils with Cucurbita pepo through the use of plant-associated bacteria and copper nanoparticles. To utilize plant growth-promoting endophytes in phytoremediation applications, it is necessary that they are cultivable in laboratory conditions. Therefore, we investigated different media and gelling agents as well as the effect of the addition of plant extract to the medium on cultivability of endophytic strains. For these purposes, the bacterial communities were identified using both cultivationdependent and cultivation-independent methods and their possible plant growthpromoting capacities were investigated. In our research, a 1/10 diluted rich 869 medium proved to yield the highest numbers of endophytes as well as the highest diversity. Furthermore, we also investigated whether adding plant extract to the bacterial growth medium enhanced the growth of bacteria that were previously stored at -80°C and had lost their ability to grow. The addition of plant extract indeed lead to a significant increase in the growth capacity of bacterial strains that were stored in glycerol. A next step in our research was to evaluate the effects of DDE on both the cultivable and total endophytic communities. We observed an increased endophytic diversity in plants that were exposed to DDE and identified several bacterial strains that could resist DDE toxicity such as Sphingomonas sp. and Stenotrophomonas sp. Recently, copper nanoparticles (CuNPs) are added to pesticides for their antifungal ability as well as their capacity to increase the uptake of pesticides into the plants. Therefore, the effects of CuNPs on plant growth, endophytic communities and DDE uptake were evaluated. Some bacterial strains showed to be sensitive to the combination of DDE and CuNPs, while others showed enhanced presence in the endophytic communities. Ten strains exhibiting both DDE-degrading and plant growth-promoting capacities were selected for a further investigation of their possible application in DDE phytoremediation. Of the 10 strains that were tested, 3 showed a good inoculation efficiency and plant growth-promoting capacity. Therefore, these three strains were selected for a DDE-degradation experiment using GCMS analysis. All three strains demonstrated a good ability to degrade DDE when inoculated in selective 284 medium supplemented with DDE. The genomes of these strains were also fully sequenced which showed them to be Sphingomonas taxi UH1, Methylobacterium radiotolerans UH1 and Enterobacter aerogenes UH1. By analyzing the genomes, several genes involved in plant growth-promotion and DDE-degradation were identified. After investigating the effects of DDE, CuNPs and endophytes separately, the combined effects of these factors on Cucurbita pepo and its DDE-uptake were evaluated. For this experiment, plants were inoculated with S. taxi UH1, M. radiotolerans UH1, E. aerogenes UH1, or a consortium of all three strains before being exposed to CuNPs and DDE. The effects on the plant growth, as well as the changes in DDE-uptake were studied. The presence of CuNPs caused a decrease of plant weight. Inoculation with the selected endophytes however, increased the plant weights to be higher than the non-inoculated control plants. The DDE concentrations of the plants exposed to CuNPs were significantly higher than those of non-exposed plants. The final experiment was to verify if the knowledge that was obtained during all previous experiments in the laboratory could be applied under field conditions. Plants were inoculated with the bacterial strains and grown for 100 days in a DDE-contaminated field. The effects of the inoculation and DDE-contamination were evaluated on both the plants and their endophytic communities (cultivable and total). The results showed a significant increase of the amount of DDE that was extracted from the soil by plants that were inoculated with the consortium of Enterobacter aerogenes UH1, Methylobacterium radiotolerans UH1, and Sphingomonas taxi UH1 in comparison to the non-inoculated control plants. Therefore, we can conclude that the phytoremediation of DDEcontaminated soils with Cucurbita pepo plants can be successfully enhanced through inoculation with DDE-degrading, plant growth promoting endophytes. In laboratory experiments, the presence of CuNPs demonstrated promising results towards increased uptake of DDE, but due to legislative constraints, the effects of CuNPs could not be evaluated in field conditions.2,2-bis(p-chlorofenyl)-1,1,1-trichloro-ethaan (DDT) werd geproduceerd en toegepast als pesticide vanaf 1939 en het gebruik ervan was tegen 1943 wereldwijd verspreid (Turusov et al., 2002). In 1974 waren er voldoende bewijzen dat DDT en zijn metabolieten, 2,2-bis(p-chlorofenyl)-1,1-dichloroethyleen (DDE) en 1,1-dichloro-2,2-bis(p-chlorofenyl)-ethaan (DDD), zeer persistent waren in het milieu en geaccumuleerd werden in de vetweefsels van hogere diersoorten met verdunning van eierschalen en endocriene verstoring als gevolg (Thomas et al., 2008), wat leidde tot verbieden van zowel het gebruik als de productie van DDT in België. DDE-toxiciteit en persistentie in het milieu worden hierdoor beschouwd als belangrijke milieuproblemen. Het hydrofobe karakter van DDE veroorzaakt een sterke absorptie aan bodempartikels waardoor het moeilijk verwijderbaar is uit de bodem. Het onderzoek van White et al. (2010) toonde het potentieel van Cucurbita pepo ssp. pepo cultivar Raven (Zucchini Raven) om verweerde DDE uit bodems te extraheren en binnen de plant te transporteren aan. De voornaamste doelstelling van dit onderzoek was om fytoremediatie van DDE-vervuilde bodems met Cucurbita pepo te verbeteren door middel van het gebruik van plant-geassocieerde bacteriën en kopernanopartikels (CuNPs). Om plantengroei-bevorderende bacteriën toe te passen in fytoremediatie is het noodzakelijk dat de bacteriën gegroeid kunnen worden in laboratoriumomstandigheden. Daarom werden verschillende media en stollingsmiddelen voor deze media getest, alsook het effect van het toevoegen van plantenextracten aan het bacterieel medium. Tijdens deze experimenten werden de bacteriële gemeenschappen geïdentificeerd door middel van cultivatie-afhankelijke en cultivatie-onafhankelijke methoden en werden hun plantengroei-bevorderende eigenschappen nagegaan. Ons onderzoek toonde aan dat een 1/10 verdund rijk 869 medium zowel de hoogste aantallen bacteriën opleverde, alsook de hoogste diversiteit aan endofyten. Verder werd onderzocht of de toevoeging van plantextract aan het medium kon leiden tot een verbeterde groei van bacteriële stammen waarvan de groeicapaciteit sterk afgenomen of zelfs verloren was na bewaring in een glyceroloplossing bij -80°C. De toevoeging van plantextract leidde inderdaad tot een significante toename van de groeicapaciteit van bacteriën die in een glycerolstock werden bewaard. Een volgende stap in het onderzoek was om de effecten van DDE op zowel de cultiveerbare als de totale endofytische gemeenschappen te evalueren aangezien dit de contaminant is waarop er gefocust werd. We stelden een toename vast van de diversiteit aan endofyten in planten die werden blootgesteld aan DDE en we identificeerden meerdere bacteriële stammen die een hoge tolerantie voor DDE vertoonden, zoals Sphingomonas sp. en Stenotrophomonas sp. Omwille van hun antifungale eigenschappen en om de opname van pesticiden in planten te verhogen worden sedert kort CuNPs toegevoegd aan pesticiden. Daarom hebben we de effecten van CuNPs op de groei van de plant, de endofytische gemeenschappen en de DDE-opname bestudeerd. Sommige bacteriële stammen werden duidelijk geïnhibeerd door de combinatie van DDE en CuNPs, terwijl anderen een verhoogde abundantie vertoonden in de endofytische gemeenschap. Tien bacteriële stammen die zowel DDEdegraderende als plantengroei-bevorderende eigenschappen vertoonden, werden geselecteerd voor verder onderzoek naar hun mogelijke toepassing in de fytoremediatie van DDE. Van de 10 stammen die getest werden, vertoonden er 3 een goede inoculatie-efficiëntie en bevordering van de groei van de planten. Deze 3 stammen werden daarom gekozen voor een DDE-afbraak-experiment gebruik makend van GCMS analyse. De 3 stammen konden DDE afbreken wanneer ze in een selectief 284 medium aangerijkt met DDE geïnoculeerd werden. De volledige genomen van deze stammen werden gesequeneerd. Dit toonde aan dat de stammen tot de soorten Sphingomonas taxi UH1, Methylobacterium radiotolerans UH1 en Enterobacter aerogenes UH1 behoren. Door analyse van de genomen konden verscheidene genen betrokken in de bevordering van de plantengroei en de afbraak van DDE geïdentificeerd worden. Nadat de effecten van DDE, CuNPs en endofyten apart werden bestudeerd, werden ook de gecombineerde effecten van deze factoren geëvalueerd. Tijdens dit experiment werden de planten geïnoculeerd met S. taxi UH1, M. radiotolerans UH1 en E. aerogenes UH1 of een consortium van de 3 stammen voordat ze werden blootgesteld aan CuNPs en DDE. De effecten op de plantengroei en de verschillen in DDE-opname werden geëvalueerd. De aanwezigheid van CuNPs veroorzaakte een afname in het gewicht van de planten. Wanneer de planten echter geïnoculeerd waren met de endofyten, nam het gewicht van de planten toe. In een finaal experiment werd de in het laboratorium vergaarde kennis getest onder veldcondities. Planten werden geïnoculeerd met de geselecteerde endofyten en gedurende 100 dagen gegroeid in een met DDE vervuild veld. De effecten van de inoculatie en de blootstelling aan DDE-vervuiling werden bestudeerd zowel op de groei van de planten als op de cultiveerbare en totale endofytische gemeenschappen. De resultaten toonden een significante toename in de hoeveelheid DDE die verwijderd werd uit de bodem door de planten geïnoculeerd met het consortium van Enterobacter aerogenes UH1, Sphingomonas taxi UH1 en Methylobacterium radiotolerans UH1 in vergelijking met de niet-geïnoculeerde controleplanten. We kunnen daardoor besluiten dat fytoremediatie van DDE-vervuilde bodem met Cucurbita pepo planten succesvol verbeterd kan worden door de inoculatie van planten met DDE-degraderende, plantengroei-bevorderende endofyten. Ook de toepassing van CuNPs toonde onder laboratoriumomstandigheden beloftevolle resultaten voor het verbeteren van fytoremediatie van DDE, maar dit kon door wettelijke beperkingen niet geëvalueerd worden onder veldcondities.Agentschap Innoveren & Onderneme
Optimization of DDE-phytoremediation by exploiting plant-associated bacteria and nanoparticles
No full textIntroduction Researchers at The Connecticut Agricultural Experiment Station observed a
remarkable difference in DDE accumulation at the subspecies level of Cucurbita pepo. C.
pepo ssp pepo accumulates DDE, while C. pepo ssp ovifera did not possess this capacity. In a
first part, this study investigates whether the the differences in DDE accumulation can be
related to differences in the plant-associated bacterial populations of the different subspecies .
Bacteria were isolated from both seeds and plants of accumulating and non-accumulating
Cucurbita pepo subspecies. The plants were exposed to 100 μg L-1 DDE.
The second part of this projects concentrates on silver nanoparticles (AgNPs) and their
capability to increase the uptake of organic contaminants by plants. Here, the possibility to
optimize DDE phytoremediation by exploiting both plant-associated bacteria as well as
AgNPs was investigated. Plants were exposed to 100 μg L-1 DDE, 500 mg L-1 AgNPs or both.
The effects of DDE and AgNPs on plant growth and on the associated bacterial populations
were investigated. Plant biomasses were determined and endophytes from both subspecies in
all conditions were isolated. All isolated bacteria were subjected to (1) genotypic
identification, (2) characterization of their plant growth promoting capacity, (3) screening for
AgNP toxicity and (4) screening for DDE degradation capacity.
Results DDE proved to have a toxic effect on plant growth, while AgNPs did not cause a
decrease in biomass. The effect on the total number of plant-associated bacteria that could be
isolated was the opposite. While DDE increased the number of endophytes in zucchini Raven,
exposure to AgNPs caused a severe decrease. Endophytes associated with zucchini Raven
demonstrated more plant growth promoting capacities than squash-associated bacteria.
Bacteria that were isolated from plants that were exposed to DDE or AgNPs showed to
experience less toxic effects when again exposed to these products.
Conclusion The DDE accumulator Zucchini Raven contains a higher number and diversity of
associated bacteria and its bacteria show more plant growth promoting capacity and potential
DDE degradation capacity than the bacteria associated with the non-DDE-accumulator squash
Zephyr. These findings and the higher DDE-uptake of zucchini Raven makes it a suitable
organism for DDE phytoremediation.
On one hand, AgNPs can be used to increase the DDE uptake of Cucurbita pepo, but on the
other hand it has severe toxic effects on the plant-associated bacteria. Therefore, a good
balance has to be discovered between the advantages and disadvantages of AgNPs for
bacteria-enhanced phytoremediation of DDE using Cucurbita pepo ssp. pepo
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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