LACK OF NITROGEN STORAGE BY PARACOCCUS-DENITRIFICANS

The uptake of ammonia and subsequent storage of nitrogen by Paracoccus denitrificans as proposed by Dunstan & Whatley (Proc. R. Soc. Lond. B 227, 429-440 (1986)) was investigated. Growth was measured as either bacterial dry mass, protein accumulation or the optical density of the culture at 550 nm. Their observation that there was continued growth of cultures after rapid ammonia depletion of their culture medium was shown to be an incorrect interpretation of the preliminary data. Because of the synthesis of poly-beta-hydroxybutyrate the optical density of the culture increased with time, but this was not accompanied by either dry mass accumulation or protein synthesis. Growth ceased after the ammonia in the medium was depleted. There is thus no need to propose the synthesis of a specific nitrogen storage compound.