2.3. Gas collection and volume measurements
Culture bottles were sealed with retroflexed serum stoppers which were tightly fitted with a syringe for efflux of gases from the culture. PVC tubule was attached tightly to the syringe for gas collection. The PVC tubule conducted gas to an upside-down burette filled with water. The burette was immersed in a beaker filled with water. Gas produced by the culture eventually accumulated in the inverted burette by displacing an equal volume of water, and was measured from the graduated divisions of the burette until no gas was released as described by Cao et al. [15].