The use of various substrates and substrate concentrations by a Hyphomicrobium sp. isolated from soil: Effect on growth rate and growth yield.

The content of Hyphomicrobium sp. was estimated from a clay loam soil using the most probable number technique with methanol as the sole carbon source. The method enumerated Hyphomicrobia as 0.2% of the total bacteria determined by acridine orange direct counts. Hyphomicrobium sp. was not able to use C-C compounds such as glucose or acetate for growth. Maximal growth yield and growth rate were obtained when the concentration of methanol was in the range of 0.5-5 mg C/liter. Substrate affinity measurements revealed Ks values of 0.8 μM and 5.8 μM when the methanol concentration was 0.5-2.5 μM and 5-200 μM, respectively. Hyphomicrobium sp. had the ability to assimilate volatile organic compounds from air for growth. A growth yield of 0.7 mg/liter cell carbon was obtained in a mineral medium that contained no additions of organic compounds but had been stored for 4 weeks in flasks, allowing volatile compounds from the air to dissolve in the medium. When air was pumped into the culture during cultivating, the growth yield was proportional to the flow rate of air into the culture.