Bacterial degradation of ortho-dimethyl phthalate ester and adaptation of escherichia coli K12 to carbon-limited growth
BACTERIAL DEGRADATION OF ortho-DIMETHYL PHTHALATE ESTER AND ADAPTATION OF Escherichia coli K12 TO CARBON-LIMITED GROWTH
for the degree of Master of Philosophy at The University of Hong Kong
in April 2004
Microbial degradation of ortho-dimethyl phthalate ester (DMP) under aerobic conditions was investigated using bacteria isolated from sewage sludge and mangrove sediment from Hong Kong Mai Po Nature Reserve. Five morphologically distinctive microorganisms were isolated from the sludge of a sewage treatment plant and tested for their ability to degrade DMP and its analogues. One of them, Comamonas acidovorans strain Fy-l, achieved the complete degradation of phthalic acid at a high concentration within a short period of time, but none was capable of degrading DMP in culture of a single species. Two consortia of microorganisms were capable of degrading DMP through the formation of monomethyl phthalate and phthalic acid. Furthermore, the Gompertz function and the Richards function were modified and used to describe the DMP degradation process, and the results indicated that the modified Richards model was better than the Gompertz model in describing DMP degradation curves. DMP was also degraded efficiently by the immobilized consortium of bacteria on membrane fibers.
A novel bacterium, strain MPsc, was isolated for degradation of DMP from the mangrove sediment. On the basis of phenotypic, biochemical and 16S rDNA gene
sequence analyses, the strain MPsc should be considered as a new bacterium at the genus level. This strain, together with Rhodococcus zopfii, also isolated from the same mangrove sediment, was able to mineralize DMP aerobically.
Degradation of DMP by consortia, isolated from both sewage sludge and mangrove sediment, followed a common two-stage hydrolysis of the ester bonds to phthalic acid by one member of the two bacteria in each consortium. Further degradation of phthalic acid required the participation of the other member. Biochemical cooperation between the two strains in each consortium allowed the complete degradation of DMP. The results suggest that the degradation of complex organic compounds, including DMP, may be carried out by several members of microorganisms working together biochemically in natural environments
Microbial growth in carbon-limited conditions was also investigated using Escherichia coli Kl2 as a model organism. N-acetyl-D-glucosamine (NAG) and arabinose were used as the sole source of carbon and energy. Metabolic evolution at a low carbon concentration led to a nearly 4-fold increase in substrate carbon affinity (Ks) for both NAG and arabinose. Adaptation to long-term carbon-limitation also resulted in a domination by 1poS-attenuated population of E. coli Kl2 with a considerable plasticity with respect to carbon utilization. The results considerably extend our understanding of microbial growth in carbon-limited conditions.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:phthalate esters biodegradation escherichia coli growth
Date of Publication:01/01/2004