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Articles

Technique for the Determination of the Rate of Ethylene Production by Pseudomonas solanacearum¹

Christen D. Upper^b

^a Department of Plant Pathology, University of Wisconsin, Madison, Wisconsin 53706, Agricultural Research Service, United States Department of Agriculture, Department of Plant Pathology, University of Wisconsin, Madison, Wisconsin 53706

A tube culture system was designed for measurement of ethylene evolved by the phytopathogenic bacterium, Pseudomonas solanacearum. The system consisted of 10 glass tubes joined together in series and coated on the inside surface with a dextrose-peptone-casamino acids agar medium. The system provided a large surface for bacterial growth in relation to the volume of air. The system was seeded with a bacterial suspension (7 x 10⁸ cells/ml) drawn through all the tubes by vacuum applied at one end and was then placed in a water bath at 30 C. Air was pumped through the system at 3 ml/min; the outlet was connected directly to the inlet port of a gas sampling loop and ethylene in the sample was determined by gas chromatography.

Maximum rate of ethylene production for a fluidal, virulent isolate of P. solanacearum (K60) was 5.5 x 10^–9 moles/min and occurred at the end of lag phase and beginning of stationary phase. Three other fluidal isolates produced ethylene at relatively low rates (2.4-6.4% that of K60). Avirulent, butyrous variants of these isolates grew as well as the virulent forms in most cases, but ethylene production rates per cell were much lower for the avirulent than for the virulent forms. Loss of virulence appears to be accompanied by lower ethylene production.

Peak CO₂ production (14.5 µmoles/min) and O₂ consumption (11.7 µmoles/min) for isolate K60 also occurred at the time when the bacterial culture was entering stationary phase. The concentrations of O₂ (11%) and CO₂ (11%) in air present at this time were thought to be neither limiting nor inhibitory to bacterial growth.

¹ Research was supported by the College of Agricultural and Life Sciences, University of Wisconsin (Project 1474), and by National Science Foundation Grant GB-31584.