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

Analysis of the endophytic lifestyle and plant growth promotion of Burkholderia terricola ZR2-12

Members of the genus Burkholderia are highly versatile bacteria that can be beneficial as well as pathogenic for their eukaryotic hosts. Furthermore, many strains exhibit a remarkable biotechnological potential. To study the ecosystem function and lifestyle of B. terricola, we analysed the interactions with plants and survival in soil as well as the mechanisms behind it. We used a combination of in vitro and ad planta assays to study Burkholderia-plant interaction and assess the role of poly-beta-hydroxybutyrate (PHB). Additionally, DsRed-labelled bacteria were analysed by confocal laser scanning microscopy (CLSM) to study root colonisation. B. terricola ZR2-12 treatment resulted in enhanced growth of sugar beet plants with a more than doubled biomass relative to the non-treated control. The strain was a remarkable good root coloniser, which was found in rhizosphere as well as endorhiza of sugar beet up to 10 log(10) CFU g(-1). Using CLSM, we observed that ZR2-12 cells form large micro-colonies along the apoplastic spaces of the root. Xylem vessels were colonised by smaller aggregates and single cells, whereas in root tips mainly single cells were present. The colonisation patterns differed strongly between older and younger parts of the roots. PHB production of ZR2-12 (up to 70% (w/w) of cell dry mass) provided a competitive advantage for rhizosphere colonisation. B. terricola ZR2-12 belongs to the plant-associated Burkholderia cluster with biotechnological potential due to its excellent root colonisation and plant growth promotion