Comparison of various measures of microbial growth kinetics in suspended and biofilm cultures during biodegradation of naphthalene.

This research focused on measurement of bacterial growth rates and activities in suspended cultures and biofilms using Pseudomonas putida (ATCC 17484) for biodegradation of naphthalene. A comparison was made of the effect of three biomass measures: optical density, total cell protein, and living cell number on the calculated rate of naphthalene disappearance. Living cell number was determined by optimizing a fluorescent staining technique and using epifluorescence microscopy. All three techniques gave similar results in terms of the specific growth rates, and in all three there was a lag time between the disappearance of naphthalene and the appearance of biomass. This was most likely a consequence of the production of intermediate products detected in the chromatograms. Inclusion of a one-hour lag time in the integrated Monod expression considerably improved the agreement between experimental and calculated values. However, further improvements to an understanding of the overall rate processes may require more detailed kinetics of the individual biochemical pathways.