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Comparing cultivation-dependent and cultivation-independent approaches for characterizing activated sludge and soil bacterial populations degrading a model pollutant, 2-chloropropionic acid (2MCPA)

Hama Chawash, Kwestan 2011. Comparing cultivation-dependent and cultivation-independent approaches for characterizing activated sludge and soil bacterial populations degrading a model pollutant, 2-chloropropionic acid (2MCPA). MPhil Thesis, Cardiff University.
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Abstract

Extensive use of organic halogenated chemicals in many areas of agriculture and industry has resulted in widespread presence of toxic and carcinogenic compounds in the environment, creating many problems. Bacteria are able to degrade these harmful compounds, primarily by production of dehalogenating enzymes using them as sole sources of carbon and energy. Little is known about microbial adaptation during -haloacid (HA) degradation. Therefore, this study aimed to investigate bacterial community and dehalogenase genes during degradation of 2-chloropropionic acid (2MCPA) in activated sludge and soil inoculated Ready Biodegradation Tests (RBT) format, using DNA based cultivation-independent and cultivation-dependent methods. Changes in the bacterial communities of activated sludge (AS) and soil (HS and LS) RBTs were monitored by analysis of bacterial 16S rRNA and HA dehalogenase (dehI & dehII) genes. Bacterial 16S rRNA gene DGGE profiles showed that several bacterial species (phylotypes) were persistent during 2MCPA degradation, whilst other phylotypes were either enriched or appeared transiently. Some changes in the bacterial communites were associated with appearance of deh genes. At lower inoculum concentration of soil (LS-RBT), 2MCPA degradation gave biphasic curve of dechlorination; the presence of a Comamonas phylotype during the initial stages of substrate degradation coincided with the presence of group II dehalogenases (dehII), and was replaced by Methylibium in the second phase of 2MCPA degradation, coinciding with the presence of a group I dehalogenases (dehI). However, in the high inoculum of soil (HS)-RBT and AS-RBT, 2MCPA degradation was completed more rapidly in a single phase, with enrichment of Herbaspirillum-like (in HS-RBT) phylotypes, and Caulobacter and Cupriavidus-like (in AS-RBT) phylotypes. Samples removed periodically from the RBTs were used to inoculate solid and liquid sub-cultures (2 or 10 mM 2MCPA) for further enrichment and isolation of 2MCPA-degrading bacteria. DGGE profiles of 16S rRNA gene sequences from the AS-RBT revealed considerable differences from those of the liquid sub-cultures, suggesting that degradation of 2MCPA was affected by and possibly determined by substrate concentration and presence of specific degraders in a system. The isolates obtained from soil and AS-RBTs, whether or not they reflected the RBT, were mainly Alphaproteobacteria, indicating the importance of these bacteria in degrading 2MCPA. Four 2MCPA-degrading bacteria, Afipia sp. KH3, Rhizobium sp. KH31, Herbaspirillum sp. KH17 and Methylobacterium sp. KH4, were isolated in this study and characterized phylogenetically and with respect to their dehalogenases. Among the genes involved in 2MCPA degradation, the sequence of dehI of strain KH17 was identical to that of dehI of Herbaspirillum sp. DA1. This study showed there is significant bias during liquid sub-culture process, and highlights the advantage of using molecular based (PCR-DGGE) methods in investigating the actual contribution of bacteria population in degrading xenobiotics (HAs). Moreover, molecular genetic analyses were useful in monitoring the enrichment and isolation possesses.

Item Type: Thesis (MPhil)
Status: Unpublished
Schools: Biosciences
Date of First Compliant Deposit: 30 March 2016
Last Modified: 19 Mar 2016 22:23
URI: https://orca.cardiff.ac.uk/id/eprint/14104

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