Bacteria-inducing legume nodules involved in the improvement of plant growth, health and nutrition

Bacteria-inducing legume nodules are known as rhizobia and belong to the class Alphaproteobacteria and Betaproteobacteria. They promote the growth and nutrition of their respective legume hosts through atmospheric nitrogen fixation which takes place in the nodules induced in their roots or stems. In addition, rhizobia have other plant growth-promoting mechanisms, mainly solubilization of phosphate and production of indoleacetic acid, ACC deaminase and siderophores. Some of these mechanisms have been reported for strains of rhizobia which are also able to promote the growth of several nonlegumes, such as cereals, oilseeds and vegetables. Less studied are the mechanisms that have the rhizobia to promote the plant health; however, these bacteria are able to exert biocontrol of some phytopathogens and to induce the plant resistance. In this chapter, we revised the available data about the ability of the legume nodule-inducing bacteria for improving the plant growth, health and nutrition of both legumes and nonlegumes. These data showed that rhizobia meet all the requirements of sustainable agriculture to be used as bio-inoculants allowing the total or partial replacement of chemicals used for fertilization or protection of crops

Phytoremediation using native plants

The unprecedented growth in industrialization has significantly increased pollution in the environment causing public health concerns. The remediation of various contaminated environmental matrices presents a global challenge. Phytoremediation using native plants can serve a dual purpose of site remediation and ecological restoration. Native plants provide an ideal residence for microbial community in their rhizosphere with enzymatic ability to accumulate, stabilize, biodegrade or volatilize various inorganic and organic contaminants. A case study that compared a native plant, Chromolaena odorata, from crude oil-polluted land in Nigeria against a referenced plant, Medicago sativa, for polycyclic aromatic hydrocarbons (PAHs) remediation is presented in this chapter. It was observed that the native plant thrived, tolerated and degraded PAHs better than the reference plant but with no significant difference in PAH degradation. The use of plants is well suited to its natural contaminated area and solar-driven, prevents erosion and eliminates secondary airborne and waterborne waste but with some challenges. Phytoremediation using native species may be effective and efficient than its non-native counterparts, and it is ecologically safer, cheaper, aesthetically pleasing, socially acceptable and easier to cultivate. Native plants in phytoremediation can be further enhanced and improved using molecular techniques to optimize the harvest time, reduce growth duration and increase biomass production and root depth

Rhizobium Presence and Functions in Microbiomes of Non-leguminous Plants

The genus Rhizobium is well known in the context of its interaction with leguminous plants. The symbiosis Rhizobium-legume constitutes a significant source of ammonia in the biosphere. Rhizobium species have been studied and applied as biofertilizers for decades in legumes and nonlegumes, due to the potential as N-fixer and plant growth promoter. Since its discovery, conventional culture-dependent techniques were used to isolate Rhizobium members from their natural niche, the nodule, and their identification was routinely performed via 16S rRNA gene and different housekeeping genes. Biotechnological advances based on the use of omics-based technologies showed that species belonging to the genus Rhizobium are keystone taxa in several diverse environments, such as forests, agricultural land, Arctic, and Antarctic ecosystems, contaminated soils and plant-associated microbiota. In this chapter, we will summarize the advances in the study of the Rhizobium genus, from culturomics strategies to modern omics methodologies, mostly based on next-generation sequencing approaches. These cutting-edge molecular approaches are fundamental in the study of the behavior of Rhizobium species in their interaction with Non-leguminous plants, supporting their potential as an ecological alternative to chemical fertilizers in the battle against Climatic Change