Cell yields of bacteria grown on methane

Several mixed cultures of methane-oxidizing bacteria have been isolated. Among them, culture HR (consisting of two gram-negative rods, one 0.5 × 1.0 μ, the other 0.8 × 2 to 3 μ) was found to be the fastest-growing and to give the highest yields. Optimal conditions for rapid growth and high cell yields from methane were found to be: 30 C, NH₄⁺ as nitrogen source, and pH 6.5. Requirements for CO₂ and Cu⁺⁺ were observed. Under these conditions, generation times of approximately 3 hr and cell yields from methane between 65 and 70% could be attained. Culture HR can utilize methane, methanol, ethyl alcohol, 1-propanol, n-butyl alcohol, and glucose, but not propane, for growth. Yeast and beef extracts are inhibitory. Carbon balances demonstrate that few if any products other than cells and CO₂ are produced from methane under the growth conditions used. Cell analyses for carbon, hydrogen, nitrogen, and amino acid content of culture HR were also made.