Rhizobacteria are capable of stimulating plant growth through a variety of mechanisms that include improvement of plant nutrition, production and regulation of phytohormones, and suppression of disease causing organisms. While considerable research has demonstrated their potential utility, the successful application of plant growth promoting rhizobacteria (PGPR) in the field has been limited by a lack of knowledge of ecological factors that determine their survival and activity in the plant rhizosphere. To be effective, PGPR must maintain a critical population density of active cells. Inoculation with PGPR strains can temporarily enhance the population size, but inoculants often have poor survival and compete with indigenous bacteria for available growth substrates. PGPR often have more than one mechanism for enhancing plant growth and experimental evidence suggests that the plant growth stimulation is the net result of multiple mechanisms of action that may be activated simultaneously. The aim of this review is to describe PGPR modes of action and discuss practical considerations for PGPR use in agriculture.

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Phytases are a group of enzymes capable of releasing phosphate from phytate, one of the most abundant forms of organic phosphate in the natural environment. Phytases can be found in many organisms; in bacteria, they are particularly described in γ-proteobacteria. In recent years, bacterial phytases have been isolated, characterized and proposed as potential tools in biotechnology. Microbial phytases have been applied mainly to animal (swine and poultry) and human foodstuffs in order to improve mineral bioavailability and food processing. Here, we summarize the current knowledge of bacterial phytases and phytase-producing bacteria, as well as their potential biotechnological applications, including new fields poorly explored, such as fish nutrition, environmental protection and plant nutrition. Despite the recognized importance in biotechnology, information on bacterial phytases and phytase-producing bacteria is clearly limited and major efforts are required to improve the knowledge of phytases present in bacteria and their utilization.

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