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Inoculum size as a factor limiting success of inoculation for biodegradation
M A Ramadan1, O M el-Tayeb, M Alexander
1Department of Agronomy, Cornell University, Ithaca, New York 14853.
Applied and Environmental Microbiology
|May 1, 1990
Summary
Introducing Pseudomonas cepacia into lake water requires a high inoculum size for effective p-nitrophenol (PNP) biodegradation. Low cell densities fail due to protozoan grazing and nutrient limitations, hindering synthetic chemical breakdown in natural environments.
Area of Science:
- Environmental microbiology
- Bioremediation of synthetic chemicals
Background:
- Synthetic chemicals like p-nitrophenol (PNP) pose environmental challenges.
- Microbial degradation is a key bioremediation strategy.
- The success of introducing specific bacterial strains into natural ecosystems is not always guaranteed.
Purpose of the Study:
- To investigate the impact of inoculum size of Pseudomonas cepacia on p-nitrophenol (PNP) biodegradation in nonsterile lake water.
- To identify factors limiting the biodegradation of synthetic chemicals by introduced bacteria in natural aquatic environments.
Main Methods:
- Assessing PNP mineralization by varying initial cell densities of Pseudomonas cepacia in lake water.
- Monitoring bacterial population dynamics and protozoan activity.
- Evaluating the effects of antimicrobial agents (cycloheximide, nystatin) and nutrient amendments (KH2PO4, NH4NO3) on biodegradation.
Main Results:
- Low inoculum sizes (330 cells/ml) of P. cepacia failed to mineralize PNP.
- Effective PNP biodegradation occurred with higher inoculum densities (3.3 x 10^4 to 3.6 x 10^5 cells/ml).
- Bacterial population decline at low densities was linked to protozoan grazing; its inhibition allowed bacterial multiplication and PNP degradation.
- Nutrient addition (KH2PO4, NH4NO3) also supported biodegradation at low cell densities.
Conclusions:
- Inoculum size is critical for the success of Pseudomonas cepacia in degrading synthetic chemicals in natural waters.
- Protozoan grazing and nutrient availability are significant factors limiting bioremediation by introduced bacteria.
- Strategies to overcome these limitations, such as increasing inoculum density or supplementing nutrients, are necessary for effective in-situ bioremediation.