(Uncorrected OCR) Abstract of the thesis entitled MOLECULAR BIOLOGY OF A CRYPTIC DEHALOGENASE FROM Burkholderia cepacia MBA4 Submitted by Laiju Sam For the degree of Doctor of Philosophy at The University of Hong Kong in July 2000 Burkholderia cepacia MBA4 has been previously shown to produce a single dehalogenase in batch culture condition. Other cryptic dehalogenases were detected in cells grown in continuous culture. In this study, one of the cryptic dehalogenases was cloned and characterised. This cryptic haloacid dehalogenase was designated Chd 1 and expressed constitutively in Escherichia coli. The structural gene, chdJ, was isolated from a 1.7-kb PstI fragment. This fragment. contains a functional promoter since the expression of chdl in E. coli is orientation independent. The nucleotide sequence of the fragment was determined and analysed and an open reading frame for 840 amino acids was identified. The nucleotide sequence of chdl did not show any homology with those of other dehalogenase genes. Comparison of the deduced amino acid sequence, however, showed significant homology, ranging from 42-50%, with the amino acid sequences of several other dehalogenases. Phylogenetic analysis indicated that Chd 1 is closely related to dehalogenase CI and dehalogenase IVa of Pseudomonas putida CBS3 and B. cepacia MBA4 respectively. 1 The recombinant Chdl had a native molecular weight of 58,000 daltons whereas the denatured molecular weight was found to be 27,000 daltons. Thus, the enzyme exists predominantly as a dimer. When the activity towards the two stereoisomers of 2-monochloropropionic acid were considered individually, the enzyme was found to be active towards the L-isomer only. The purified enzyme was most active towards monobromoacetic acid with specific activities of 5.44, 1.5, 4.56, and 1.95 J!mole of halide released/min/mg protein for monobromoacetic acid, 2-monobromopropionic acid, monochloroacetic acid and 2-monochloropropionic acid respectively. Maximum activity of the enzyme was observed at pH 6.5. The enzyme was found to be thermolabile. chdl was cloned in the T7 RNA polymerase driven pRSET A and Irc promoter based pPROEXHT expression vectors. However, no significant expression of chdl was obtained in these systems. Chd 1 differed from other dehalogenases in having a long leader sequence. This leader sequence contains a potential signal peptidase cleavage site. This is a property of periplasmic enzymes. In order to detect the unprocessed molecules of Chd 1, chdl was expressed in the temperature-sensitive E. coli strain IT 41 (lep9-mutant). This strain contains a mutation in the leader peptidase gene. The leader peptidase is inactive in this strain at the non-permissive temperature of o 42 C. Precursor molecules of Chd 1 was detected in cultures shifted to this non- permissive temperature. Periplasmic fractions isolated from E. coli harboring chdl were found to contain the active dehalogenase. 11 / abstract / toc / Botany / Doctoral / Doctor of Philosophy

published_or_final_version / Botany / Doctoral / Doctor of Philosophy

Thesis (PhD)--Macquarie University, Division of Environmental & Life Sciences, Department of Biological Sciences, 2008. / Bibliography: p. 257-274. / Literature review -- General materials and methods -- Characterisation of strain collection -- Distribution of integrons and gene cassettes in pseudomonas -- Genomic context of pseudomonas integrons -- Evolutionary analysis of pseudomonas spp. integrons 199 -- Final discussion -- Appendix -- References. / Integrons associated with mobile genetic elements have played a central role in the emergence and spread of multiple antibiotic resistance in many pathogenic bacteria. However, the discovery of integrons in the chromosomes of diverse, non-pathogenic bacteria suggests that integrons have a broader role in bacterial evolution. The Pseudomonas stutzeri species complex is a well studied model for bacterial diversity. Members of the complex are genetically closely related, but sub-taxa are not able to be defined by exclusively shared sets of phenotypic characters. Rather, on the basis of total DNA:DNA similarity, Ps. stutzeri strains have been divided into 17 different groups (termed genomovars). Two Ps. stutzeri strains have been found to contain Chromosomal Integrons (CIs). This thesis involved exploration of the hypothesis that a CI was present in the common ancestor of the Ps. stutzeri species complex and assessed the impact of integrons on diversity across all Pseudomonads. The history and significance of integrons is discussed in Chapter 1 as part of a literature review, and general materials and methods are provided in Chapter 2. Chapters 3 - 6 comprise the sections in which data generated during my PhD project are presented. A comprehensive analysis of the relationships between the strains being analysed is presented in Chapter 3. In Chapter 4, results of PCR and hybridisation screening for integrons across the strain collection are presented. In Chapter 5 the recovery of additional integrons and in depth sequence analysis of the recovered integrons are described. Finally, Chapter 6 contains statistical analyses of integron-associated genes and Chapter 7 contains a final discussion the most significant findings. Twenty-three Pseudomonas spp. strains were screened for the presence of integrons. All but three were found to contain integron-like sequences; however, most integron sequences recovered contained inactivated core integrons. viii Despite having a chromosomal locus, integrons in Pseudomonas were found to have properties indicative of frequent horizontal transfer. Evidence was also obtained which suggests that integrons have been acquired at the same locus on multiple independent occasions. This has not been observed in other families of chromosomal integrons and suggests that the loci at which integrons in Pseudomonas are found are hotspots for recombination. / Mode of access: World Wide Web. / xiii, 274 p. ill

Pseudomonas is a diverse genus of Gram-negative bacteria that includes pathogens of plants, insects, and humans as well as environmental strains with no known pathogenicity. Pseudomonas fluorescens itself encompasses a heterologous group of bacteria that are prevalent in soil and on foliar and root surfaces of plants. Some strains of P. fluorescens suppress plant diseases and the genomic sequences of many biological control strains are now available. I used a combination of bioinformatic and phylogenetic analyses along with mutagenesis and biological assays to identify and compare the TonB-dependent outer-membrane proteins (TBDPs) of ten plant-associated strains of P. fluorescens and related species. TBDPs are common in Gram-negative bacteria, functioning in the uptake of ferric-siderophore complexes and other substrates into the cell. I identified 14 to 45 TBDRs in each strain of P. fluorescens or P. chlororaphis. Collectively, the ten strains have 317 TBDPs, which were grouped into 84 types based upon sequence similarity and phylogeny. As many as 13 TBDPs are unique to a single strain and some show evidence of horizontal gene transfer. Putative functions in the uptake of diverse groups of microbial siderophores, sulfur-esters, and other substrates were assigned to 28 of these TBDP types based on similarity to characterized orthologs from other Pseudomonas species. Redundancy of TBDP function was evident in certain strains of P. fluorescens, especially Pf-5, which has three TBDPs for ferrichrome/ferrioxamine uptake, two for ferric-citrate uptake and three for heme uptake. Five TBDP types are present in all ten strains, and putative functions in heme, ferrichrome, cobalamin, and copper/zinc uptake were assigned to four of the conserved TBDPs. The fluorescent pseudomonads are characterized by the production of pyoverdine siderophores, which are responsible for the diffusible UV fluorescence of these bacteria. Each of the ten plant-associated strains of P. fluorescens or P. chlororaphis has three to six TBDPs with putative roles in ferric-pyoverdine uptake (Fpv). To confirm the roles of the six Fpv outer membrane proteins in P. fluorescens Pf-5, I introduced deletions into each of the six fpv genes in this strain and evaluated the mutants and the parental strain for heterologous pyoverdine uptake. I identified at least one ferric-pyoverdine that was taken up by each of the six Fpv outer-membrane proteins of Pf-5. By comparing the ferric-pyoverdine uptake assay results to a phylogenetic analysis of the Fpv outer-membrane proteins, I observed that phylogenetically-related Fpv outer-membrane proteins take up structurally-related pyoverdines. I then expanded the phylogenetic analysis to include nine other strains within the P. fluorescens group, and identified five additional types of Fpv outer-membrane proteins. Using the characterized Fpv outer-membrane proteins of Pf-5 as a reference, pyoverdine substrates were predicted for many of the Fpv outer-membrane proteins in the nine other strains. Redundancy of Fpv function was evident in Pf-5, as some pyoverdines were recognized by more than one Fpv. It is apparent that heterologous pyoverdine recognition is a conserved feature, giving these ten strains flexibility in acquiring iron from the environment. Overall, the TBDPs of the P. fluorescens group are a functionally diverse set of structurally-related proteins present in high numbers in many strains. While putative functions have been assigned to a subset of the proteins, the functions of most TBDPs remain unknown, providing targets for further investigations into nutrient uptake by P. fluorescens spp.. The work presented here provides a template for future studies using a combination of bioinformatic, phylogenetic, and molecular genetic approaches to predict and analyze the function of these TBDPs. / Graduation date: 2012