Vegetative reproduction | EPFL Graph Search

Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is any form of asexual reproduction occurring in plants in which a new plant grows from a fragment or cutting of the parent plant or specialized reproductive structures, which are sometimes called vegetative propagules. Many plants naturally reproduce this way, but it can also be induced artificially. Horticulturists have developed asexual propagation techniques that use vegetative propagules to replicate plants. Success rates and difficulty of propagation vary greatly. Monocotyledons typically lack a vascular cambium, making them more challenging to propagate. Background Plant propagation is the process of plant reproduction of a species or cultivar, and it can be sexual or asexual. It can happen through the use of vegetative parts of the plants, such as leaves, stems, and roots to produce new plants or through growth from specialized vegetative plant parts. Whil

Nanopore Integrated Nanogaps for DNA Detection

Axel Fanget, László Forró, Sergey Khlybov, Arnaud Magrez, Aleksandra Radenovic, Floriano Traversi

A high-throughput fabrication of sub-10 nm nanogap electrodes combined with solid-state nanopores is described. These devices should allow concomitant tunneling and ionic current detection of translocating DNA molecules. We report the optimal fabrication parameters in terms of dose, resist thickness, and gap shape that allow easy reproduction of the fabrication process at wafer scale. The device noise and current voltage characterizations performed and the influence of the nanoelectrodes on the ionic current noise is identified. In some cases, ionic current rectification for connected or biased nanogap electrodes is also observed. In order to increase the extremely low translocation rates, several experimental strategies were tested and modeled using finite element analysis. Our findings are useful for future device designs of nanopore integrated electrodes for DNA sequencing.

American Chemical Society2014

Implantation of Bacillus pseudomycoides Chromate Transporter Increases Chromate Tolerance in Bacillus subtilis

Imrich Barak, Barbora Bártová, Rizlan Bernier-Latmani, Zuzana Chromiková

Chromium of anthropogenic origin contaminates the environment worldwide. The toxicity of chromium, a group I human carcinogen, is greatest when it is in a hexavalent oxidation state, Cr(VI). Cr(VI) is actively transported into the cell, triggering oxidative damage intracellularly. Due to the abundance of unspecific intracellular reductants, any microbial species is capable of bio-transformation of toxic Cr(VI) to innocuous Cr(III), however, this process is often lethal. Only some bacterial species are capable of sustaining the vegetative growth in the presence of a high concentration of Cr(VI) and thus operate as self-sustainable bioremediation agents. One of the successful microbial Cr(VI) detoxification strategies is the activation of chromate efflux pumps. This work describes transplantation of the chromate efflux pump from the potentially pathogenic but highly Cr resistant Bacillus pseudomycoides environmental strain into non-pathogenic but only transiently Cr tolerant Bacillus subtilis strain. In our study, we compared the two Bacillus spp. strains harboring evolutionarily diverged chromate efflux proteins. We have found that individual cells of the Cr-resistant B. pseudomycoides environmental strain accumulate less Cr than the cells of B. subtilis strain. Further, we found that survival of the B. subtilis strain during the Cr stress can be increased by the introduction of the chromate transporter from the Cr resistant environmental strain into its genome. Additionally, the expression of B. pseudomycoides chromate transporter ChrA in B. subtilis seems to be activated by the presence of chromate, hinting at versatility of Cr-efflux proteins. This study outlines the future direction for increasing the Cr-tolerance of non-pathogenic species and safe bioremediation using soil bacteria.

2022

Metal reduction and sporulation in Desulfotomaculum reducens

Elena Cristina Dalla Vecchia

The genera Desulfotomaculum and Clostridium, belonging to the phylum Firmicutes, comprise Gram-positive, low G+C genomic content, anaerobic, spore- forming bacteria. Desulfotomaculum is a metabolically and environmentally versatile genus capable of growing fermentatively as well as by respiring sulfate. D. reducens is also capable of metal reduction and has been reported to conserve energy from this process. In this thesis, iron (Fe(III)) reduction by D. reducens in the presence of pyruvate or lactate as electron donors was investigated. When pyruvate is present, D. reducens grows fermentatively. If Fe(III) is present, it can act as an electron sink alternative to protons and consume excess reducing equivalents accumulated during pyruvate oxidation. Electron transfer to Fe(III) by D. reducens in the presence of pyruvate is mediated by a soluble electron carrier, likely riboflavin, released by cells during fermentation. This mechanism allows the microorganism to reduce extracellular, solid phase Fe(III) even if it is not directly accessible by physical contact. In the presence of lactate, D. reducens is unable to conserve significant energy from electron donor oxidation and Fe(III) reduction. In contrast to pyruvate, during lactate oxidation, no redox-active compound is released by the cells, and extracellular, solid phase Fe(III) can only be reduced by direct contact. This implies that a surface exposed reductase must be present in D. reducens cells. The investigation of the surface proteome of this organism led to the identification of three proteins, most likely localized to the cell surface, potentially involved in Fe(III) reduction. One is a heterodisulfide reductase subunit A, a putative intermediate in the Fe(III) reduction chain. The second is a membrane-associated hydrogenase. The third protein is annotated as alkyl hydroperoxide reductase although its actual function may be thiol-disulfide oxidoreduction; several lines of evidence suggest the involvement of the latter in metal reduction by D. reducens. Clostridium species are widespread in the environment and are capable of utilizing a great variety of organic substrates for fermentative growth, while they are unable to conserve energy through respiration. However, they can reduce terminal electron acceptors to eliminate excess reducing equivalents from fermentation. Among the electron acceptors used by Clostridium spp., are metals, such as iron and uranium (U(VI)). One species whose vegetative cells are capable of U(VI) reduction is C. acetobutylicum, although little information is available on the mechanism underlying this process. In this thesis, the potential involvement of the spores of C. acetobutylicum in U(VI) reduction is probed. It was found that the spores of this species can reduce the radionuclide, and that to do so they require the presence of an unidentified soluble compound released by growing cells and H2 as the electron donor. The involvement of spores in metal reduction is very interesting because generally spores are considered not to interact directly with the surrounding environment. In fact, spores are dormant, thus metabolically inactive, cells. Spore formation is a cell differentiation process activated in response to environmental stress and conditions that are hostile to vegetative growth. Sporulation has been extensively studied and characterized in Bacillus subtilis, for which a model has been developed. Some information is also available on sporulation in the clostridia. In this thesis, a genomic investigation of sporulation in the Desulfotomaculum genus was undertaken. The B. subtilis model was used as a reference and the information on Clostridium as a comparison. Significant similarities were found in the core regulatory process across genera, while some differences were identified in the initiation of sporulation. Substantial differences were highlighted in the spore structural proteins.