Promising bacterial genera for agricultural practices: an insight on plant growth-promoting properties and microbial safety aspects

In order to address the ever-increasing problem of the world's population food needs, the optimization of farming crops yield, the combat of iron deficiency in plants (chlorosis)and the elimination/reduction of crop pathogens are of key challenges to solve. Traditional ways of solving these problems are either unpractical on a large scale (e.g. use of manure)or are not environmental friendly (e.g. application of iron-synthetic fertilizers or indiscriminate use of pesticides). Therefore, the search for greener substitutes, such as the application of siderophores of bacterial source or the use of plant-growth promoting bacteria (PGPB), is presented as a very promising alternative to enhance yield of crops and performance. However, the use of microorganisms is not a risk-free solution and the potential biohazards associated with the utilization of bacteria in agriculture should be considered. The present work gives a current overview of the main mechanisms associated with the use of bacteria in the promotion of plant growth. The potentiality of several bacterial genera (Azotobacter, Azospirillum, Bacillus, Pantoea, Pseudomonas and Rhizobium)regarding to siderophore production capacity and other plant growth-promoting properties are presented. In addition, the field performance of these bacteria genera as well as the biosafety aspects related with their use for agricultural proposes are reviewed and discussed.