Evaluation of bacterial strategies to degrade non-desorbable naphthalene in natural and artificial s...

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" Evaluation of bacterial strategies to degrade non-desorbable naphthalene in natural and artificial sorbents "
Mohammad Sajjad T. C. Voice

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	54320
Doc. No	:	TL24274
Call number	:	‭3171521‬
Main Entry	:	Mohammad Sajjad
Title & Author	:	Evaluation of bacterial strategies to degrade non-desorbable naphthalene in natural and artificial sorbents\ Mohammad Sajjad
College	:	Michigan State University
Date	:	2005
Degree	:	Ph.D.
student score	:	2005
Page No	:	162
Abstract	:	Recently, several studies demonstrated that bacteria might be able to degrade sorbed contaminants without prior desorption in water. Mechanisms including extra-cellular biomaterial production, chemotaxis/motility, and adhesion were hypothesized to be responsible for the enhanced bioavailability of these compounds. However, experimental evidence to confirm this bacterial potential in the soil system has not been verified. In this study we evaluated the role of the selected bacterial phenotypes in naphthalene degradation in a sorbent-slurry system. The rate and extent of sorbed-phase naphthalene was determined in the sorbent-slurry systems inoculated separately with the wild-type Psuedomonas putida G7 and the mutant strains (with one or other missing phenotypes), and the results were compared for evaluating the role of these phenotypes. The experimental results showed that wild-type P. putida G7 degraded sorbed naphthalene at a rate and extent greater than what can be removed from both Tenax beads and serial extraction methods. Activity of extra-cellular enzyme was ruled out during the biodegradation study since the experiments with bacterial filtrates did not show any degradation of observable free naphthalene during the incubation period. The possible effect of biomaterial on the sorption/desorption parameters was also observed to be negligible. The amount of the biomaterial produced during the bio-availability studies was small enough to have caused any significant effect on mass transfer parameters. This study demonstrates that the effect of chemotaxis/motility phenotypes could not be observed in natural soils under both stirred and quiescent conditions. In a stirred system, the mixing had masked the role of chemotaxis/motility due to maintenance of isotropic concentration and mixing-mediated adhesion of cells to sorbent particles. Under quiescent conditions, wild-type P. putida G7 and mutant strains were not able to degrade the non-desorbable fraction of naphthalene because of pore size exclusion and retardation of bacterial cell in natural soil. However, the role of chemotaxis/motility was apparent in the system containing activated carbon, where wild-type degraded the non-desorbable naphthalene fraction at a greater rate and extent as compared with the system containing mutant strains. The difference in uptake rates between wild-type and mutant strains was due to the presence of a significant concentration gradient at the soil/water interface as a result of a large pool of non-desorbable naphthalene fraction in the activated carbon. This study also attempts to examine factors affecting bacterial attachment that, consequently, enhances bio-degradation. The wild type P. putida G7 and the mutant strains, deficient in adhesion, were observed to have equally accessed non-desorbable fraction of naphthalene and degraded the fraction at an equal rate and extent. Three orders of decrease in molar concentration of the buffer medium did not affect the rate and extent of sorbed phase naphthalene degradation by P. putida G7. Important attachment phenotypes of P. putida G7 did not play any significant role in enhanced bioavailability of sorbed phase naphthalene. The results of this study suggest that factors promoting bacterial attachment (i.e. removal of exopolysaccharides, presence of flagella and reduction of buffer medium concentration) do not contribute to biodegradation of non-desorbable fraction of soil-sorbed naphthalene in a mixed soil-slurry system.
Subject	:	Health and environmental sciences; Applied sciences; Artificial sorbents; Biodegradation; Chemotaxis; Naphthalene; Pseudomonas putida; Environmental engineering; Environmental science; 0768:Environmental science; 0775:Environmental engineering
Added Entry	:	T. C. Voice
Added Entry	:	Michigan State University