Biological filtration processes for the removal of the cyanobacterial toxin, cylindrospermopsin

Wijesundara, Shiromani Wasantha Kumari (2007). Biological filtration processes for the removal of the cyanobacterial toxin, cylindrospermopsin PhD Thesis, School of Medicine, The University of Queensland.

       
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Author Wijesundara, Shiromani Wasantha Kumari
Thesis Title Biological filtration processes for the removal of the cyanobacterial toxin, cylindrospermopsin
School, Centre or Institute School of Medicine
Institution The University of Queensland
Publication date 2007-11-12
Thesis type PhD Thesis
Supervisor Moore, Michael
Newcombe, Gayle
O'Donohue, Mark
Shaw, Glen
Subjects 320000 Medical and Health Sciences
Formatted abstract Cylindrospermopsin (CYN) is a hepatotoxic alkaloid produced by certain freshwater cyanobacteria. It has been distributed mainly in tropical and subtropical regions, but also in the northern temperate zone of the world. Cylindrospermopsis raciborskii and Aphanizomenon ovalisporum are the main CYN producing cyanobacteria in Australia. The presence of CYN in drinking water has the potential to cause human illness from consumption of contaminated water. The elimination of this toxin is very important in the drinking water treatment industry.
CYN has been shown to be degraded by chlorine, but can result in the formation of chlorinated by-products. Application of natural aquatic bacteria to degrade CYN is highly important to the water industry as it is incorporating natural degradation principles. At present, very little is known about the application of biodegradation in the removal of CYN. In this project the optimum conditions for CYN biodegradation and the ability for use of biologically active filters to eliminate CYN were investigated.
This thesis presents evidence for the applicability of a Biologically Active Filtration Plant (BAFP) sited at North Pine Dam, Queensland, Australia in removing both soluble toxin and the toxin producing C. raciborskii cells when the dam water was filtered through both roughing filter and sand filter. CYN elimination was shown for extra-cellular CYN and Cylindrospermopsis raciborskii cells throughout the year without showing any adverse effect from seasonal variations. According to the laboratory culture experiments, the total time for degradation of CYN and the lag period in each culture was different because these bacteria may require a certain period of time for
their establishment. No lag phase was observed before degradation commenced at the end of the study period indicating the endemic bacterial population was induced by the frequent exposure to CYN. These findings suggest that under conditions employed in this study; biologically active sand filtration has the potential to be an effective treatment process for the complete removal of CYN in drinking water.
The CYN degradation characteristics were also investigated with special reference to the culture characteristics of CYN degrading bacteria. As a culture medium, Jaworski’s medium was the best for the CYN degrading bacteria. The study of biodegradation of purified CYN with the comparison of biodegradation of cell free extract CYN indicated that cell free extract CYN has some dissolved organic matter that can enhance microbial growth. CYN degrading bacteria could degrade a wide range of concentrations of CYN with an initial slow degradation phase up to 5 days and then rapid degradation phase until the degradation was completed. Biodegradation of CYN was determined to be a zero order reaction for the CYN concentration ranges 0- 400 �g L-1, showing biphasic degradation kinetics with an initial slow degradation phase up to 5 days and then rapid degradation phase until the degradation was completed. Furthermore, CYN degrading bacteria could degrade the CYN analog, deoxy-CYN indicating that the structural differences between CYN and deoxy-CYN do not have any impact on biodegradation process of these compounds.
Phylogenetic analysis based on 16S rRNA gene sequence revealed that the main CYN degrading strain was Sinorhizobium species. The bacterium could degrade CYN as a carbon source; therefore the utilisation of CYN by the bacterium as a food source was indicated. The degradation process of this strain was affected by environmental factors such as pH and temperature. For maximum degradation efficiency, this strain required
a neutral pH condition and a temperature of 300C. Under such conditions, a treatment system established with this strain could be effective to eliminate CYN in drinking water.
Collectively, these observations strongly suggest that there is significant potential for application of biologically active filtration plants to drinking water treatment to eliminate CYN based on the biodegradation characteristics and the efficiency of the filtration plant studied. With the potential increase of toxic by-products generated with the use of chemicals in Australian water treatment plants, this study provides valuable new information for the use of natural degradation processes, particularly since minimal research in this area has been conducted.


 
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