https://web.science.uu.nl/pmi/publications/PDF/2012/TiPS-Berendsen-2012.pdf

The rhizosphere microbiome and plant health

Plant growth-promoting bacterial endophytes.

Phytoremediation and rhizoremediation of organic soil contaminants : Potential and challenges

Exploiting plant–microbe partnerships to improve biomass production and remediation

In the last decade, there has been an increase in research on improving the ability of plants to remove environmental pollution. Genes from microbes, plants, and animals are being used successfully to enhance the ability of plants to tolerate, remove, and degrade pollutants. Through expression of specific bacterial genes in transgenic plants, the phytotoxic effects of nitroaromatic pollutants were overcome, resulting in increased removal of these chemicals. Overexpression of mammalian genes encoding cytochrome P450s led to increased metabolism and removal of a variety of organic pollutants and herbicides. Genes involved in the uptake or detoxification of metal pollutants were used to enhance phytoremediation of this important class of pollutants. Transgenic plants containing specific bacterial genes converted mercury and selenium to less toxic forms. In addition to these transgenic approaches, the use of microbes that live within plants, termed endophytes, also led to improved tolerance to normally phytotoxic chemicals and increased removal of the pollutants. Bacteria that degraded a herbicide imparted resistance to the herbicide when inoculated into plants. In another study, plants harboring bacteria capable of degrading toluene were more tolerant to normally phytotoxic concentrations of the chemical, and transpired less of it into the atmosphere. This review examines the recent advances in enhancing phytoremediation through transgenic plant research and through the use of symbiotic endophytic microorganisms within plant tissues.

http://depts.washington.edu/envaplab/papers/TansleyReviewDoty.pdf

Enhancing phytoremediation through the use of transgenics and endophytes

Poplar and willow are economically-important, fast-growing tree species with the ability to colonize nutrient-poor environments. To initiate a study on the possible contribution of endophytes to this ability, we isolated bacteria from within surface-sterilized stems of native poplar (Populus trichocarpa) and willow (Salix sitchensis) in a riparian system in western Washington state. Several of the isolates grew well in nitrogen-limited medium. The presence ofnifH, a gene encoding one of the subunits of nitrogenase, was confirmed in several of the isolates including species ofBurkholderia, Rahnella, Sphingomonas, andAcinetobacter. Nitrogenase activity (as measured by the acetylene reduction assay) was also confirmed in some of the isolates. The presence of these diazotrophic microorganisms may help explain the ability of these pioneering tree species to grow under nitrogen limitation.

https://courses.washington.edu/cfr523/documents/SymbiosisPoplarWillowEndophytes.pdf

Diazotrophic endophytes of native black cottonwood and willow

Small, volatile hydrocarbons, including trichloroethylene, vinyl chloride, carbon tetrachloride, benzene, and chloroform, are common environmental pollutants that pose serious health effects We have developed transgenic poplar (Populus tremula × Populus alba) plants with greatly increased rates of metabolism and removal of these pollutants through the overexpression of cytochrome P450 2E1, a key enzyme in the metabolism of a variety of halogenated compounds The transgenic poplar plants exhibited increased removal rates of these pollutants from hydroponic solution When the plants were exposed to gaseous trichloroethylene, chloroform, and benzene, they also demonstrated superior removal of the pollutants from the air In view of their large size and extensive root systems, these transgenic poplars may provide the means to effectively remediate sites contaminated with a variety of pollutants at much faster rates and at lower costs than can be achieved with current conventional techniques

https://www.pnas.org/content/pnas/104/43/16816.full.pdf

Enhanced phytoremediation of volatile environmental pollutants with transgenic trees

Endophytic bacteria associated with sweet potato plants (Ipomoea batatas (L.) Lam.) were isolated, identified and tested for their ability to fix nitrogen, produce indole acetic acid (IAA), and exhibit stress tolerance. Eleven different strains belonging to the genera, Enterobacter, Rahnella, Rhodanobacter, Pseudomonas, Stenotrophomonas, Xanthomonas and Phyllobacterium, were identified. Four strains were shown to produce IAA (a plant growth hormone) and one strain showed the ability to grow in nitrogen free medium and had the nitrogenase subunit gene, nifH. To determine if IAA production by the endophytes had any role in protecting the cells against adverse conditions, different stress tests were conducted. The IAA producer grew well in the presence of some antibiotics, UV and cold treatments but the response to pH, osmotic shock, thermal and oxidative treatments was the same for both the IAA producer and the no IAA producer. To determine if IAA produced by the strains was biologically relevant to plants, cuttings of poplar were inoculated with the highest IAA producing strain. The inoculated cuttings produced roots sooner and grew more rapidly than uninoculated cuttings. These studies indicate that endophytes of sweet potato plants are beneficial to plant growth.

/pdf/characterization-of-bacterial-endophytes-of-sweet-potato-53j4igsfm8.pdf

Characterization of bacterial endophytes of sweet potato plants

Growth enhancement and drought tolerance of hybrid poplar upon inoculation with endophyte consortia

Endophytes have been isolated from a large diversity of plants and have been shown to enhance the remediation efficiency of plants, but little information is available on the influence of endophytic bacteria on phytoremediation of widespread environmental contaminants such as polycyclic aromatic hydrocarbons (PAHs). In this study we selected a naturally occurring endophyte for its combined ability to colonize plant roots and degrade phenanthrene in vitro. Inoculation of two different willow clones and a grass with Pseudomonas putida PD1 was found to promote root and shoot growth and protect the plants against the phytotoxic effects of phenanthrene. There was an additional 25–40% removal of phenanthrene from soil by the willow and grasses, respectively inoculated with PD1 when compared to the uninoculated controls. Fluorescent microscopy using fluorescent protein tagging of PD1 confirmed the presence of bacteria inside the root tissue. Inoculation of willows with PD1 consistently improved the growth and he...

Zareen Khan

Papers

Diazotrophic endophytes of native black cottonwood and willow

Enhanced phytoremediation of volatile environmental pollutants with transgenic trees

Characterization of bacterial endophytes of sweet potato plants

Growth enhancement and drought tolerance of hybrid poplar upon inoculation with endophyte consortia

Degradation, Phytoprotection and Phytoremediation of Phenanthrene by Endophyte Pseudomonas putida, PD1