CELL DENSITY-DEPENDENT ADAPTATION OF PSEUDOMONAS-PUTIDA TO BIODEGRADATION OF P-NITROPHENOL

A Pseudomonas putida isolated from a natural microbial community adapted to p-nitrophenol (PNP) underwent an extended lag period in pure cultures exposed to PNP. The length of the lag was inversely proportional to the cell density. Length of the lag period was not affected by PNP concentrations over a range of 15-5000 mug L-1. In experiments where the total population was held constant while the volume of the culture fluid was varied, the more dilute suspensions adapted much more slowly. This result suggested that a ''factor'' must accumulate in the culture before initiation of PNP degradation. Hydroquinone, an early intermediate in PNP degradation, accumulated transiently in culture fluid during adaptation of the P. putida to PNP. When hydroquinone was added to cultures along with PNP, the length of the lag period was reduced. Addition of hydroquinone did not shorten lag periods at cell concentrations below 10(5) cfu mL-1. This suggests that hydroquinone is not the actual inducer or effector but that it is converted by the cells to the active component. We propose that the lag period before biodegradation of PNP is caused by delayed induction of enzymes. Induction is dependent upon the accumulation of hydroquinone or a factor whose release is stimulated by hydroquinone.