Pressure transducer method for measuring gas production by microorganisms

Abstract

A simple method for measuring gas production by microorganisms by using a pressure transducer to sense pressure buildup was developed and tested with members of the coliform group. The test system consisted of a 5.0 lb/in2 pressure transducer and a pressure equalizer valve attached to the metal cap of a test tube (20 by 150 mm); gas pressure was recorded on a strip chart recorder. Gas pressure response curves consisted of (i) a lag period with no marked increase in pressure, (ii) a rapid pressure buildup period, and (iii) a leveling off period. A linear relationship was established between inoculum size and length of the lag period. Cultures shaken at 200 oscillations/min showed a marked increase in rate of gas release over stationary cultures. Cell concentrations at the time of rapid buildup in pressure were 108/ml. Mean maximum pressure recordings, lb/in2 per 10 ml of broth, were: Enterobacter aerogenes, 3.70; Citrobacter intermedium, 2.70; and Escherichia coli, 2.10. Mean CO2 concentrations, ppm of headspace gas, for E. coli were: (i) 2,000 at time of inoculation, (ii) 25,000 at time of rapid buildup in pressure, and (iii) 150,000 at maximum pressure.