| Summary: | 碩士 === 國立高雄師範大學 === 生物科技系 === 103 === Soil functional hydrocarbon-degrading enzymes play a relatively important role in diesel weathering processes. Thus, this study would like to analyze distribution and temporal change of gene expression of major functional degrading enzymes in diesel-contaminated soils, and determine effects of environmental factors (e.g. pH, water content, and concentration of organic carbon, total nitrogen and total phosphorous) in order to understand the possible biodegrading pathway in diesel weathering processes.
After the six-month experimental period, the experimental group of unsterilized diesel-contaminated soil with peat soil addition showed the highest diesel degradation rate among sixteen experimental groups. The sterilized experimental groups had lower number of bacterial colonies than the unsterilized ones. The soil pH decreased from pH 7 to pH 5 and the water content decreased from 15% to 5%, indicating the growth of some bacteria might be affected. The organic carbon content of soils without peat soil addition was about 2% and that of soils with peat soil addition was about 4%. The soils with peat soil addition contained higher total nitrogen than those without. The soils from the southern Taiwan contained higher total nitrogen than those from the northern Taiwan. The concentrations of total phosphorous were lower than 500 g/g dw, except for the soil from the southern Taiwan in the initial stage. The C/P and N/P increased with time in the soils from the northern Taiwan, but only shown for the soil from the southern Taiwan in the initial three-month stage. The C/P and N/P became suitable for growth of microorganisms in the later experimental period.
The quantitative results of gene expression of functional degrading enzymes showed that the soils from the southern Taiwan had higher gene expression of functional degrading enzymes (with relative ratio >1) than those from the northern Taiwan. The alkB for degrading n-alkane expressed in the initial four months. The xylE presented in the soils without peat soil addition in the 4th and 5th month. The nahAc was found in the six-month experimental period and expressed higher (with relative ration >1 for mRNA expression) in soils without peat soil addition. The bphA expressed after the 3rd month in soils without peat soil addition, but it expressed in the first month in the soil with peat soil addition. The bphA1 presented only in the later months. The xylM only found in the Formosa diesel-contaminated southern soils in the 1st and 2nd month. The ntnM only found in the two types of soils. The tmoF in soils without peat soil addition expressed in the initial two months, but that in soil with peat soil addition expressed in the six-month experimental period. To sum up, the alkB expressed in the initial months, but the other genes of functional degradation enzymes expressed during the six-month experimental period. It indicated that microorganisms would firstly degrade n-alkane, and then degrade aromatic hydrocarbons.
The gene expression of functional degrading enzymes was significantly positively correlated to concentrations of petroleum hydrocarbons and total phosphorous, and bacterial colonies. It indicated that the diesel-contaminated soil contained enough carbon and phosphorous to improve the growth of bacteria with functional degrading enzymes.
|
|---|
