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Action of autochthonous bacteria on the decay of enteric viruses in groundwater

Wall, Katrina Joy (2006) Action of autochthonous bacteria on the decay of enteric viruses in groundwater. PhD thesis, Murdoch University.

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      Abstract

      With global freshwater supplies under pressure, viable water reuse methods are being examined to assist in improving water supplies. Municipal effluent is an ideal source for water reclamation as it is consistent in quality and quantity. The health aspects of water reuse have been identified as an issue of concern, in particular the potential presence of enteric viruses. Managed Aquifer Recharge (MAR) is a method that can aid water reclamation by recharging water such as treated effluent into a suitable aquifer. Research into the removal of pathogenic contaminants by natural processes within aquifers, namely the action of autochthonous bacteria, has led to the consideration that MAR could be used to assist in the removal of microbial pathogens. Pathogens have been demonstrated to be removed during residence in groundwater, but the presence of active autochthonous groundwater bacteria are required for significant removal rates to occur.

      The aim of this research was to investigate the interaction between autochthonous groundwater bacteria (AGB) and the enteroviruses Poliovirus type 1, Coxsackievirus B3 and Adenovirus B41. It was established that these viruses decrease in number in the presence of AGB but the mechanisms causing this decrease are poorly understood. Experiments were designed to examine how the individual AGB caused decay of the viruses.

      In this study AGB were isolated and tested for their ability in increase the decay of the viruses. It was determined that 27 % (17/63) of the isolated AGB influenced viral decay. The AGB isolates varied in their influence with only 3 out of 17 isolates being able to cause of the decay of both poliovirus and coxsackievirus. Similar variations in decay were observed for adenovirus. Decay times for all three viruses varied amongst the AGB and between the viruses.

      Experiments were undertaken to characterise the mechanism causing the antiviral activity of four groundwater isolates (1G, 3A, 4B and 9G) under varying conditions and treatments to give insight into the compounds or mechanisms responsible for viral decay. This would indicate whether compounds produced by the AGB responsible for viral decay were closely associated to bacterial cells (perhaps membrane bound), independent of metabolic activity, heat labile or were enzymatic in nature.

      The influence of enzyme inhibiters and heat treatment indicated that viral degradation is caused by compounds that are enzymatic in nature. As viral numbers were monitored by nucleic acid copy numbers rather than via infectivity assays, the viral protein coats must be the first step in degradation followed by the removal of the viral nucleic acid. This two step process would require both protease and nuclease enzymes to result in loss of viral numbers as measured by RT-PCR/PCR.

      Further characterisation and identification of these four bacterial isolates was also carried out. Three out of the four isolates were sequenced and analysed using partial 16S rRNA gene sequences to determine their phylogenetic relationships compared to related organisms. Isolate 3A was placed in the order Burkholderiales. Isolate 4B was placed in the family Xanthomonadaceae. Isolate 9G was placed in the family Rhizobiaceae. Isolate 1G was only partially sequenced and preliminary identification placed it in the phylum Bacteriodetes.

      Understanding of the processes carried out by AGB within an aquifer during MAR using reclaimed waters will aid in increasing the viability of this water reuse process. If important natural processes could be utilised to remediate any potential pathogens, the health concerns with reclaimed waters could be addressed and solved simply through prescribed retention times within the aquifer. Key species of AGB may even be utilised as markers to assess the suitability of an aquifer for MAR.

      Publication Type: Thesis (PhD)
      Murdoch Affiliation: School of Biological Sciences and Biotechnology
      Supervisor: Toze, Simon and O'Hara, Graham
      URI: http://researchrepository.murdoch.edu.au/id/eprint/1299
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