To assess the suitability of a mineral medium selected from the literature for high cell density cultivations of Priestia megaterium DSM 509 (ultimately for producing PHA), fermentations were planned and tested in a (2 L) bioreactor. After few hours of a batch culture, growth was limited despite an efficient oxygenation and the relative abundance of macronutrients, suggesting trace elements (TE) deficiencies. They had to be increased to achieve higher growth rates and cell densities. Growth was improved by adding up to 10 times more TE as maximum growth rate increased from 0.20 to 2.36 g L−1 h−1, but eventually growth limitations occurred. Major and trace minerals were therefore determined by ICP-OES. These analyses showed that the selected medium was deficient mainly in Co, Mn and Zn. Requirements for 11 minerals could then be assessed and used to formulate a new mineral medium. Tested in a fed-batch culture assigned to a specific growth rate of 0.2 h−1, it allowed P. megaterium to grow in 8 h during the batch phase without being limited until the exhaustion of glucose. In the fed-batch phase, high cell densities of 53.6 g L−1 were reached after 10 h with a space-time yield of 2.96 g L−1 h−1.