You Are What You Can Find to Eat: Bacterial Metabolism in the Rhizosphere

Metabolism is the underpinning force that sustains life. Within the rhizosphere it is a cyclic process, with substrates flowing between different compartments of the complete soil-plant-microbe system. The physiochemical and structural environment of the rhizosphere is shaped by a combination of plant genotype and soil type, both of which strongly impact the microbial community structure. External influences such as seasonality, the degree of water saturation and anthropomorphic inputs also play a role. Together these factors influence the flux of metabolites through the rhizosphere community, which in turn impacts on plant growth, development and disease. In this review, the focus is on metabolism within the bacterial population of the rhizosphere, since this group covers every type of plant-microbe interaction: from obligately symbiotic to destructively pathogenic, and includes those have little or no direct impact on plant hosts. The focus of the review is on metabolic functions that occur in the rhizosphere either during bacteria-plant interactions or bacteria-bacteria interactions and mainly covers heterotrophic metabolism of organic substrates. As such, many of the autotrophic (and phototrophic) reactions of inorganic compounds are not included.