Recent Advances in Bacterial Amelioration of Plant Drought and Salt Stress

The recent literature indicates that plant growth-promoting bacteria (PGPB) employ a range of mechanisms to augment a plant’s ability to ameliorate salt and drought stress. These mechanisms include synthesis of auxins, especially indoleacetic acid, which directly promotes plant growth; synthesis of antioxidant enzymes such as catalase, superoxide dismutase and peroxidase, which prevents the deleterious effects of reactive oxygen species; synthesis of small molecule osmolytes, e.g., trehalose and proline, which structures the water content within plant and bacterial cells and reduces plant turgor pressure; nitrogen fixation, which directly improves plant growth; synthesis of exopolysaccharides, which protects plant cells from water loss and stabilizes soil aggregates; synthesis of antibiotics, which protects stress-debilitated plants from soil pathogens; and synthesis of the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which lowers the level of ACC and ethylene in plants, thereby decreasing stress-induced plant senescence. Many of the reports of overcoming these plant stresses indicate that the most successful PGPB possess several of these mechanisms; however, the involvement of any particular mechanism in plant protection is nearly always inferred and not proven

Bacterial Modulation of Plant Ethylene Levels

A focus on the mechanisms by which ACC deaminase-containing bacteria facilitate plant growth.Bacteria that produce the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, when present either on the surface of plant roots (rhizospheric) or within plant tissues (endophytic), play an active role in modulating ethylene levels in plants. This enzyme activity facilitates plant growth especially in the presence of various environmental stresses. Thus, plant growth-promoting bacteria that express ACC deaminase activity protect plants from growth inhibition by flooding and anoxia, drought, high salt, the presence of fungal and bacterial pathogens, nematodes, and the presence of metals and organic contaminants. Bacteria that express ACC deaminase activity also decrease the rate of flower wilting, promote the rooting of cuttings, and facilitate the nodulation of legumes. Here, the mechanisms behind bacterial ACC deaminase facilitation of plant growth and development are discussed, and numerous examples of the use of bacteria with this activity are summarized

The use of plant growth-promoting bacteria to prevent nematode damage to plants

Plant-parasitic nematodes have been estimated to annually cause around US $173 billion in damage to plant crops worldwide. Moreover, with global climate change, it has been suggested that the damage to crops from nematodes is likely to increase in the future. Currently, a variety of potentially dangerous and toxic chemical agents are used to limit the damage to crops by plant-parasitic nematodes. As an alternative to chemicals and a more environmentally friendly means of decreasing nematode damage to plants, researchers have begun to examine the possible use of various soil bacteria, including plant growth-promoting bacteria (PGPB). Here, the current literature on some of the major mechanisms employed by these soil bacteria is examined. It is expected that within the next 5\u201310 years, as scientists continue to elaborate the mechanisms used by these bacteria, biocontrol soil bacteria will gradually replace the use of chemicals as nematicides

Recent developments in the study of plant microbiomes

To date, an understanding of how plant growth-promoting bacteria facilitate plant growth has been primarily based on studies of individual bacteria interacting with plants under different conditions. More recently, it has become clear that specific soil microorganisms interact with one another in consortia with the collective being responsible for the positive effects on plant growth. Different plants attract different cross-sections of the bacteria and fungi in the soil, initially based on the composition of the unique root exudates from each plant. Thus, plants mostly attract those microorganisms that are beneficial to plants and exclude those that are potentially pathogenic. Beneficial bacterial consortia not only help to promote plant growth, these consortia also protect plants from a wide range of direct and indirect environmental stresses. Moreover, it is currently possible to engineer plant seeds to contain desired bacterial strains and thereby benefit the next generation of plants. In this way, it may no longer be necessary to deliver beneficial microbiota to each individual growing plant. As we develop a better understanding of beneficial bacterial microbiomes, it may become possible to develop synthetic microbiomes where compatible bacteria work together to facilitate plant growth under a wide range of natural conditions

Mycorrhizal-Bacterial Amelioration of Plant Abiotic and Biotic Stress

Soil microbiota plays an important role in the sustainable production of the different types of agrosystems. Among the members of the plant microbiota, mycorrhizal fungi (MF) and plant growth-promoting bacteria (PGPB) interact in rhizospheric environments leading to additive and/or synergistic effects on plant growth and heath. In this manuscript, the main mechanisms used by MF and PGPB to facilitate plant growth are reviewed, including the improvement of nutrient uptake, and the reduction of ethylene levels or biocontrol of potential pathogens, under both normal and stressful conditions due to abiotic or biotic factors. Finally, it is necessary to expand both research and field use of bioinoculants based on these components and take advantage of their beneficial interactions with plants to alleviate plant stress and improve plant growth and production to satisfy the demand for food for an ever-increasing human population

Evaluación de factibilidad de mejoras empleando control predictivo basado en modelos en reactores de biodiésel

La producción de biocombustibles, en especial de biodiesel, es un proceso costoso y que requiere especial cuidado en el control de cada una de las etapas de obtención del mismo. Es una práctica habitual el uso de controladores convencionales como el PID, sin embargo los sistemas comerciales hoy ofrecen la oportunidad de incorporar otros controladores que mejoran notablemente el desempeño del comportamiento a lazo cerrado del sistema. En este contexto, se presentarán los ensayos preliminares realizados con diferentes estructuras de control sobre el reactor tales como feedforward, cascada, compensador de tiempo muerto (compensador Smith) y con particular énfasis, control predictivo basado en modelos (Model Based Predictive Control, MPC). La primera etapa requiere disponer del modelo dinámico de un reactor de biodiésel que se implemente para simular los diferentes escenarios en que deberá funcionar. El concepto es que el mismo sea capaz de adaptarse a las condiciones operativas específicas de plantas con diferente capacidad operativa. Es importante explotar la capacidad de simulación que poseen los controladores comerciales para disponer de una herramienta eficiente para la toma de decisiones. Se mostrarán los resultados alcanzados empleando plataformas académicas de diseño y su posterior configuración en el controlador comercial PCS7 de Siemens.Fil: Gamalero, Marcelo. Universidad Nacional de Rosario. Facultad de Cs.exactas Ingenieria y Agrimensura; Argentina;Fil: Luppi, Patricio Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Conicet - Rosario. Instituto Rosario de Investigaciones En Ciencias de la Educación; Argentina; Universidad Nacional de Rosario. Facultad de Cs.exactas Ingenieria y Agrimensura; Argentina;Fil: Basualdo, Marta Susana. Universidad Tecnológica Nacional. Regional Rosario; Argentina; Consejo Nacional de Invest.cientif.y Tecnicas. Centro Cientifico Tecnol.conicet - Rosario. Centro Int.franco Arg.d/cs D/l/inf.y Sistem.

Phytoremediation of a highly arsenic polluted site, using pteris vittata L. And arbuscular mycorrhizal fungi

Phytoremediation is a promising green technique for the restoration of a polluted environment, but there is often a gap between lab and field experiments. The fern, Pteris vittata L., can tolerate a high soil arsenic concentration and rapidly accumulate the metalloid in its fronds. Arbuscular mycorrhizal fungi (AMF) are mutualistic fungi that form a symbiosis with most land plants\u2019 roots, improve their growth, and induce stress tolerance. This paper reports the results obtained using P. vittata inoculated with AMF, to extract Arsenic (As) from an industrial site highly contaminated also by other pollutants. Two experiments have been performed. In the first one, AMF colonized ferns were grown for two years under controlled conditions in soil coming from the metallurgic site. Positive effects on plant health and As phytoextraction and accumulation were detected. Then, considering these results, we performed a three year in situ experiment in the industrial site, to assess the remediation of As at two different depths. Our results show that the colonization of P. vittata with AMF improved the remediation process of As with a significant impact on the depth 0\u20130.2 m

Phytodepuration of Pyroligneous Liquor: A Case Study

Wastewaters generated by the pyrolytic process require treatments to reduce the risks of contamination in rivers, lakes, and coastal waters. Utilizing constructed wetlands is one of the possible approaches according to a Circular Economy System. Plant Growth-Promoting Bacteria (PGPB) and Arbuscular Mycorrhizal Fungi (AMF) can improve plant growth and enhance the bioremediation of wastewater. Two experiments were set up: in the first, a pilot mesocosm was designed to evaluate the effects of a consortium of AM fungi and a PGPB strain on Phragmites australis. After 60 days, the highest plant growth was obtained after inoculation with the combination of microorganisms. In the second experiment, a constructed wetland was built to remediate wastewaters from gasification plant. The plants were efficient in scavenging biological oxygen demand (BOD5), chemical oxygen demand (COD), total fat and oils, hydrocarbons, phenols, aldehydes, surfactants, fluorides, sulfites, sulfates, nitrate, and phosphorus. These data suggest that inoculation of P. australis with AMF and PGPB strains significantly improve the depuration process of wastewaters from gasification plants via constructed wetlands

Anti-bacterial prenylated phenols from the Kurdish medicinal plant Onobrychis carduchorum (Fabaceae)

Onobrychis carduchorum C.C. Towns. is a plant widely employed in the Kurdish traditional medicine, to cure inflammations and other skin diseases. We isolated ten different phenolic metabolites from an acetone extract of leaves and flowers. The phenolic compounds belong to three different classes, i.e.: 1. iso-flavones, having a genistein skeleton; 2. flavanones, bearing a naringenin skeleton; 3. dihydro-stilbenes. Many of them have a prenyl unit on an aromatic ring. The above compounds have been found to date mostly in other Fabaceae, as Glycyrrhiza glabra L. (liquorice)1. However, their bioactivities are largely unknown. In this work we reported a strong inhibition activity on the growth of Staphylococcus aureus, a well-known human pathogen. In particular, compound (Fig. 1) shows an inhibitory activity on growth, comparable to that of vancomycin, using the agar-diffusion standard method

Effects of compost amendment on glycophyte and halophyte crops grown on saline soils: Isolation and characterization of rhizobacteria with plant growth promoting features and high salt resistance

Soil salinization and desertification due to climate change are the most relevant challenges for the agriculture of the 21st century. Soil compost amendment and plant growth promoting rhizobacteria (PGP-R) are valuable tools to mitigate salinization and desertification impacts on agricultural soils. Selection of novel halo/thermo-tolerant bacteria from the rhizosphere of glicophytes and halophytes, grown on soil compost amended and watered with 150/300 mM NaCl, was the main objective of our study. Beneficial effects on the biomass, well-being and resilience, exerted on the assayed crops (maize, tomato, sunflower and quinoa), were clearly observable when soils were amended with 20% compost despite the very high soil electric conductivity (EC). Soil compost amendment not only was able to increase crop growth and biomass, but also their resilience to the stress caused by very high soil EC (up to 20 dS m 121 ). Moreover, compost amendment has proved itself a valuable source of highly halo-(4.0 M NaCl)/thermo tolerant rhizobacteria (55\u25e6C), showing typical PGP features. Among the 13 rhizobacterial isolates, molecularly and biochemically characterized, two bacterial strains showed several biochemical PGP features. The use of compost is growing all around the world reducing considerably for farmers soil fertilization costs. In fact, only in Italy its utilization has ensured, in the last years, a saving of 650 million euro for the farmers, without taking into account the environment and human health benefits. Furthermore, the isolation of halo/thermo-tolerant PGPR strains and their use will allow the recovery and cultivation of hun-dreds of thousands of hectares of saline and arid soils now unproductive, making agriculture more respectful of agro-ecosystems also in view of upcoming climate change