Inorganic phosphate solubilization by rhizosphere bacteria in a Zostera marina community

Abstract

Actively growing Zostera marina plants had a greater rhizosphere inorganic phosphate solubilizing potential than dormant plants. Rhizosphere bacteria that were capable of calcium phosphate solubilization were obligate aerobes and numbered approximately 4 × 108 colony-forming units/g dry weight root. Bacterial isolates solubilized calcium phosphate when cultured with glucose as the sole carbon and energy source but not when cultured with amino acids. Both calcium phosphate (hydroxyapatite) and glucose were found in sea grass bed sediment. Acetic acid was also detected from roots plus clinging sediment, from sediment, and from cultured bacterial isolates in a glucose-supplemented medium. The minimum concentration of acetic acid that showed detectable solubilization of calcium phosphate was 10−5 M. It is suggested that acetic acid, a product of glucose metabolism in the rhizosphere flora, is responsible for phosphate solubilization in the environment.