Methylobacterium organophilum can use nitrogen in the form of ammonium ions ((NH4)(2)SO4 and NH4Cl) and from nonammonium sources such as glycine, alanine, peptone, and yeast extract. When potassium was limited, significantly more PHB was produced when the ammonium ion was the nitrogen source rather than a nonammonium form. With ammonium, the amount of PHB produced was 0.50 similar to 0.53 g PHB/1 or 52.0 similar to 53.2% of the dry cell weight. If nitrogen was from a nonammonium source, the respective values were 0.04 similar to 0.06 g PHB/1 or 8.1 similar to 11.3% of dry cell weight. When ammonium sulfate was the sore source of nitrogen under potassium-limited conditions, cell growth and PHB accumulation increased as the pH increased from 6.0 to 7.5. Cell growth and PHB amount at pH 7.5 were 2.50 g dry cell weight/1 and 1.40 g PKB/1, respectively.