Preadapted inocula for limiting the risk of errors in biodegradability tests

Area of Science:

• Environmental Microbiology
• Bioremediation
• Chemical Engineering

Background:

• Standard 28-day biodegradability tests can be unreliable with low initial biodegrading populations.
• Xenobiotic compounds require a sufficient number of biodegraders for timely positive test results.
• Initial microbial concentration critically influences the lag phase in biodegradation assays.

Purpose of the Study:

• To investigate the impact of initial bacterial concentration on the lag time of para-nitrophenol biodegradation tests.
• To evaluate the effect of adapted Pseudomonas putida density on biodegradation kinetics.
• To determine optimal conditions for reliable and efficient biodegradability testing.

Main Methods:

• Experiments were conducted using adapted Pseudomonas putida with para-nitrophenol as the sole carbon source.
• Varied initial concentrations (X0) of P. putida were used to measure lag times.
• The influence of river water addition on lag time and biodegradation rate was assessed.

Main Results:

• Lag time decreased logarithmically with increasing bacterial density (y = 63.5 - 5.7(log10X0)).
• Addition of river water further shortened lag times and increased biodegradation rates (1.29 to 2.11 mgC L-1 hr-1).
• Adapted inocula at 10^5 cells/L ensured a 99.9% probability of a positive test response.

Conclusions:

• Higher initial adapted bacterial concentrations are crucial for meeting the 28-day biodegradability test timeframe.
• Adapting mixed inocula before testing is the most effective strategy to increase biodegraders.
• Achieving a high probability of positive test results requires only a moderate density of adapted cells.