All fossil fuels contain varying levels of sulfur compounds which are undesirable because they cause environmental pollution, corrosion, acid rain and lead to health problems. There is strict international legislation for the permissible levels of sulfur compounds in fossil fuels. The aim of this research therefore was the biocatalyst development for biodesulfurisation using two approaches. In the first approach, Rhodococcus erythropolis IGTS8-5 and IGTS8-5G were immobilised in porous coke particles and tested in repeated cycles successfully. Both bacterial strains grew well in the chemically defined medium with glucose as the main carbon and energy source and the model sulfur compound dibenzothiophene (DBT) as the sole sulfur source. 0.8 g of cells was immobilized on 250 g of coke particles without refreshing the medium over 72 h while 1.8 g of cells were immobilised on 250 g of coke when the media was refreshed every 24 hours for 120 h after the initial immobilisation batch of 72h. The latter, were used repeatedly in twelve consequtive batch desulfurisation cycles during which the biodesulfurisation activity progressively decreased from over 95% removal of 100 ppm DBT to around 45% removal. DBT removal is often expressed in terms of 2-hydroxybiphenyl which is the end product of biodesulfurisation. The biodesulfurisation activityof immobilised bacteria was equivalent to 310 umol 2-HBP h-1g-1 dry cell weight during the first hour. Freely suspended cells on the other hand exhibited biodesulfurisation activity equivalent to 91 umol 2-HBP h-1g-1 dry cell weight. Unfortunately, after the first 24 h, the activity of the immobilised cells decreased to 12 umol 2-HBP h-1g-1 dry cell weight. Use of plant cell cultures for biodesulfurisation is the other novel aspect of this work. Armoracia rusticana (horse radish) cell culture was chosen as the novel biocatalyst since this plant is a well known source of peroxidase enzyme which is involved in the biodesulfurisation metabolism according to the literature on bacterial biodesulfurisation. Arabidospsis thaliana (thale cress) was also used since its genome is completely sequenced and it is a model organism in genomics studies. Our results indicate that cell suspensions of both plants did show biodesulfurisation activity by reducing the level of sulfur compounds, mainly DBT and other three derivatives from both aqueous and oil phase. When compared to the bacteria, in terms of DBT consumption, the activity of A. rusticana was calculated as 55 umol DBT h-1 g-1 DCW and 65 umol DBT h-1 g-1 DCW for A. thaliana while in bacteria it was 91 umol DBT h-1 g-1 DCW for IGTS8-5 and 73 umol DBT h-1 g-1 DCW for IGTS8-5G. Transcriptomics analysis of the plant cell cultures after exposure to the DBT when compared to control cultures showed alterations in gene expression levels several of which were related to sulfur metabolism and transmembrane transporters of sulfate.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:576883 |
| Date | January 2013 |
| Creators | Al Yaqoub, Zakariya |
| Contributors | Mavituna, Ferda |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/biocatalyst-development-for-biodesulfurization(77967e83-b529-4f1a-b3f4-2e2607cb4f4f).html |
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