Les bactéries appartenant au complexe Burkholderia cepacia (Bcc) provoquent des infections sévères chez les personnes atteintes de mucoviscidose. L'infection peut varier d'une forme asymptomatique à une forme plus aiguë pouvant entraîner une pneumonie nécrosante et une septicémie, connue sous le nom de syndrome cepacia. Afin d'étudier les infections causées par le Bcc, nous avons développé un nouveau modèle in vivo, l'embryon de poisson zèbre. Nous avons montré que B. cenocepacia K56-2 pouvait se répliquer dans les macrophages et causer une infection aiguë mortelle pour les embryons. En revanche, B. stabilis LMG14294 induit une infection persistante chez les embryons. Dans cette étude, nous avons montré que les macrophages jouaient un rôle-clé dans la multiplication de K56-2 et dans l'induction d'une réponse inflammatoire MyD88-dépendante, caractérisée par la surexpression des gènes codant pour Cxcl8 (ou IL-8) et l'IL-1b. En l'absence de macrophages, les bactéries sont incapables de se multiplier durant les premières 24h de l'infection, ce qui donne un avantage pour la survie des embryons. L'absence de MyD88 induit aussi l'augmentation de la survie des embryons infectés par K56-2. Mais de manière paradoxale, les bactéries se multiplient mieux chez les embryons myd88-/- mutants que chez les embryons sauvages. Ceci suggère que ce n'est pas le nombre de bactéries qui est important pour l'infection, mais que c'est la réponse inflammatoire excessive causée par cette infection qui entraîne la mort des embryons. Afin d'avoir une vision globale des changements d'expression des gènes de l'hôte durant l'infection, nous avons effectué une expérience de RNAseq. Comme attendu, l'infection aiguë se caractérise par une importante modulation du transcriptome de l'hôte qui augmente avec le temps. A l'opposé, l'infection persistante n'induit que très peu de changements. La réponse immunitaire innée, et en particulier la voie des TLR, ainsi que l'apoptose sont très fortement activées durant une infection aiguë. Pour sa part, B. stabilis module essentiellement les gènes codant pour le système du complément.Le rôle critique des macrophages lors d'une infection par Bcc chez les poissons zèbre est en accord avec les récentes observations cliniques. Ceci suggère que le stade intracellulaire de B. cenocepacia et la réponse inflammatoire qui s'ensuit peuvent être des cibles pour le développement de nouvelles thérapies permettant de lutter contre cette infection. / Bacteria belonging to the Burkholderia cepacia complex (Bcc) can cause chronic infection with periods of acute exacerbation and sometimes fatal necrotizing pneumonia (“cepacia syndrome”) in individuals with cystic fibrosis (CF), and are associated with poor prognosis. Here, we exploited the exciting possibilities for in vivo non-invasive imaging of Bcc infection in transparent zebrafish embryos, with an innate immune system with remarkable similarity to that of humans, and numerous genetic and genomic tools to study the role of host phagocytes and the innate immune response in the pro-inflammatory character of the infection.We show that macrophages play a critical role in intracellular multiplication of B. cenocepacia K56-2 and induction of a MyD88-dependent fatal inflammatory response, characterised by high levels of cxcl8 and il1b expression. Surprisingly, in sharp contrast to the situation found for infections with other pathogens including Mycobacterium marinum and Staphylococcus aureus, in the absence of macrophages, K56-2 survived but was unable to replicate in the first 24 h, which resulted in a significant pro-survival advantage to the host compared to wild type embryos that died within 2 to 3 days. The Toll-like receptor (TLR) pathway is a major arm of the cell-mediated innate immune response with MyD88 as a key adaptor protein involved in the production of pro-inflammatory cytokines. We found that the absence of MyD88 also provided a pro-survival effect to the embryos after infection with K56-2. Paradoxically, the bacteria replicated better in myd88-/- mutant than wild type embryos, suggesting that it is not bacterial burden per se, but the inflammatory response that kills the embryos. Interestingly, cxcl8 and il1b expression were not significantly induced during the first 7 hours in the myd88-/- mutant while a strong induction was seen in control embryos, suggesting that a Myd88-dependent inflammatory response during early macrophage stages significantly contributes to fatal infection.Next, we performed RNAseq to analyse global changes in host gene expression during acute and persistent infection induced by K56-2 and B. stabilis LMG14294 respectively. Whereas acute infection was characterised by strong modulation of host gene expression increasing over time, persistent infection showed modulation of only a small set of genes. TLR and apoptosis signaling pathways were amongst the strongly activated groups during acute infection, in line with the strong inflammatory character of K56-2. During persistent infection, the major differentially expressed gene set concerned genes encoding complement proteins. The critical role for macrophages in Bcc infection in zebrafish is in agreement with recent clinical observations. We suggest that the intracellular stages of B. cenocepacia and the ensuing inflammatory response are essential targets to explore for the development of new therapies to combat this infection.

Orientador: Gabriela Alves Macedo / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-18T14:05:52Z (GMT). No. of bitstreams: 1 Messas_AnaLuizaFanchini_M.pdf: 999204 bytes, checksum: 0d58e169b0435d28b5a6d07b71f613c0 (MD5) Previous issue date: 2011 / Resumo: O ácido fítico é a principal fonte de armazenamento de fósforo em cereais e legumes, sendo que sua forma sal é denominada fitato. O fitato não é digerido pelo trato gastrointestinal de animais monogástricos e, na alimentação humana, o fitato é considerado um fator antinutricional devido à sua capacidade quelante para vários metais e por ligar-se às proteínas, conseqüentemente diminuindo a biodisponibilidade de proteínas e de minerais nutricionalmente importantes, como o zinco, ferro, cálcio, entre outros. Uma das estratégias mais efetivas para a redução do conteúdo de fitato em rações animais e alimentos tem sido a utilização de enzimas exógenas degradadoras de fitato, as fitases. Sendo assim, durante os últimos 20 anos intensificaram-se os estudos em busca de novas fontes desta enzima. A fitase está amplamente distribuída na natureza, sendo encontrada em animais, plantas e micro-organismos. A enzima presente em plantas é menos resistente ao tratamento térmico e é menos estável às condições fisiológicas do trato gastrointestinal, já a de microorganismos pode resistir a altas temperaturas, dependendo da linhagem. Neste estudo, realizou-se a produção, otimização do meio e das condições de cultivo e caracterização de fitase produzida pela bactéria Burkholderia sp. Foi definido como o meio de cultivo otimizado para a produção de fitase de Burkholderia sp. em frascos agitados em 72 horas de fermentação: fitato de sódio 0,075%, sacarose 0,16%, peptona bacteriológica 0,2%, MgSO4.7H2O 0,05%, KCl 0,05%, FeSO4.7H2O 0,0001%, MnSO4.H2O 0,00075% e CaCl2 0,01%. Foi possível aumentar a produção de fitase em 110% (1,01 U/mL para 2,12 U/mL). As condições de cultivo (agitação e temperatura) otimizadas para produção de fitase em frascos agitados foram 37°C e 250 rpm, após 48 horas de fermentação. Na caracterização bioquímica, a fitase apresentou pH ótimo em 5,5 e pH de estabilidade na faixa de 3 a 7, após 1 hora de incubação à 50°C. Apresentou temperatura ótima à 60ºC e mostrou-se estável após 1 hora de tratamento em temperaturas entre 25 e 50°C, demonstrando 40% de redução da atividade após 1 hora de tratamento à 60ºC. No estudo do efeito de íons, utilizando a concentração de 10 mM para os sais testados, os resultados mais expressivos foram o aumento da atividade de fitase em 41% com a adição de íons Ba2+ e a redução da atividade de fitase em 98% e 96%, respectivamente, com a adição de íons Fe2+ e Zn2+, inibindo quase totalmente a enzima. Para a concentração de 1 mM dos sais, a adição dos íons Mn2+, Fe2+, Cu2+, Zn2+ e Fe3+ causou reduções significativas de atividade de fitase, em 61%, 45%, 45%, 31% e 30%, respectivamente. A fitase produzida por Burkholderia sp. apresentou valores de Km e Vmax de 0,02 mM e 6,20 'mol Pi/min/mg, respectivamente / Abstract: Phytic acid is the main source of phosphorus storage in cereals and legumes, and its salt is known as phytate. Phytate is not digested by the gastrointestinal tract of monogastric animals and, in food for human consumption, phytate is considered an antinutritional factor because of its ability in chelating various metals and binding to proteins, thereby reducing the bioavailability of proteins and nutritionally important minerals as zinc, iron, calcium, and others. One of the most effective strategies for reducing phytate content in animal feed and food for human consumption has been the use of exogenous enzymes that degrade phytate, the phytases. Thus, during the last 20 years, the studies to discover new sources of this enzyme have been intensified. Phytase is widely distributed in nature, being found in animals, plants and microorganisms. The enzyme present in plants is less resistant to heat treatment and is less stable under physiological conditions of the gastrointestinal tract, since the microorganisms can withstand high temperatures, depending on the strain. In this study, it was made the production, the optimization of the medium of culture and growing conditions and characterization of phytase produced by the bacteria Burkholderia sp. It was defined as the culture medium optimized for the production of phytase of Burkholderia sp. in shaken flasks, in 72 hours of fermentation: sodium phytate 0.075%, sucrose 0.16%, bacteriological peptone 0.2%, MgSO4.7H2O 0.05%, KCl 0.05%, FeSO4.7H2O 0.0001%, MnSO4.H2O 0.00075% e CaCl2 0.01%. It was possible to increase the production of phytase in 110% (1.01 U/mL to 2.12 U/mL). The growing conditions (rotation and temperature) optimized for production of phytase in shaken flasks were 250 rpm and 37°C, after 48 hours of fermentation in shaker. In biochemical characterization, phytase showed pH optimum at 5.5 and estability in the pH range of 3 to 7, after 1 hour of incubation at 50°C. Phytase showed optimum temperature at 60°C and remained stable after 1 hour of treatment at temperatures between 25°C and 50°C, showing 40% of reduction of the activity after 1 hour of treatment at 60°C. In the study of the effect of ions, using the concentration of 10 mM for the salts tested, the most importants results were the increase of the activity of phytase in 41% with the addition of Ba2+ and the decrease of the activity of phytase in 98% and 96%, respectively, with the addition of Fe2+ and Zn2+, almost completely inhibiting the enzyme. For the concentration of 1 mM of the salts, the addition of Mn2+, Fe2+, Cu2+, Zn2+ and Fe3+ caused significant reductions in activity of phytase, in 61%, 45%, 45%, 31% and 30%, respectively. Phytase produced by Burkholderia sp. presented values of Km and Vmax of 0.02 mM e 6.20 'mol Pi/min/mg, respectively / Mestrado / Ciência de Alimentos / Mestre em Ciência de Alimentos

L’insecte phytophage Riptortus pedestris, appartenant au sous-ordre des Hétéroptères, est un ravageur notoire de cultures agricoles en Asie du sud-est qui se nourrit préférentiellement de plants de soja. Cette punaise est associée à une bactérie symbiotique du genre Burkholderia nommée Burkholderia insecticola, localisée dans une région spécifique de l’intestin de l’insecte appelée la région M4. Cette région M4, organisée en cryptes, constitue l’organe symbiotique dans lequel le symbiote prolifère de manière extracellulaire. Cette interaction favorise la croissance et le développement de la punaise. Récemment, il a été montré que Riptortus produit des peptides antimicrobiens au sein des cryptes, appelés “crypt-specific cysteine-rich peptides” ou peptides CCR pour lesquels le symbiote est particulièrement résistant. Il a été proposé que les peptides antimicrobiens de l’hôte,incluant les peptides CCR, participent à la colonisation spécifique de l’organe symbiotique par B. insecticola. Dans ce travail, une approche Tn-seq a été utilisée pour identifier les gènes bactériens impliqués dans la résistance aux peptides antimicrobiens et dans la symbiose. Dans un premier temps, la robustesse de la méthode Tn-seq a été évaluée en identifiant le génome essentiel de B. insecticola. Puis dans un second temps, les facteurs bactériens impliqués dans la résistance aux peptides antimicrobiens ont été caractérisés via une approche gènes-candidats et l’approche Tn-seq. Dans une dernière partie, une expérience de Tn-seq in vivo a permis d’évaluer l’ampleur du goulot d’étranglement sur la population symbiotique lors de l’infection de l’organe symbiotique et d’identifier les facteurs symbiotiques impliqués dans la colonisation de R. pedestris. / The phytophagous insect Riptortus pedestris, belonging to the Heteroptera suborder, is a notorious crop pest in South-Eastern Asia which feeds preferentially on soybean plants. This bean bug is associated with a bacterial symbiont, a specific Burkholderia species named Burkholderia insecticola, located in the M4 region of the insect’s midgut. This M4 region is organized in crypts and constitutes the symbiotic organ where the symbiont proliferates extracellularly. This interaction promotes the growth and the development of the bean bug. Recently, it was demonstrated that Riptortus produces antimicrobial peptides in the midgut crypts called crypt-specific cysteine-rich peptides (CCR) for which the bacterial symbiont demonstrates a high resistance profile. It was proposed that host antimicrobial peptides, including the CCR peptides, contribute to the specific colonization of the symbiotic organ by B. insecticola. In this work, a Tn-seq approach was used to find bacterial fitness genes involved in antimicrobial peptide resistance and symbiosis. First, the robustness of the Tn-seq method was assessed by identifying the essential genome of B. insecticola. Second, the bacterial factors for antimicrobial peptide resistance were characterized, based on both a candidate-gene and the Tn-seq approach. Finally, a Tn-seq in vivo experiment was performed to reveal the infection bottleneck effect on the symbiotic population and to identify the bacterial symbiosis factors for the colonization of R. pedestris.

Les bactéries appartenant au complexe Burkholderia cepacia (Bcc) sont des pathogènes opportunistes intracellulaires qui causent des infections pulmonaires chez les patients atteints de mucoviscidose, aggravant leur pronostic clinique. Ces infections pulmonaires sont caractérisées par des périodes chroniques avec des exacerbations intermittentes détériorant la fonction pulmonaire, et pouvant causer des nécroses broncho-pulmonaires et septicémies fatales reconnues sous le nom du “Syndrome Cepacia”. Ces bactéries intrinsèquement multi-résistantes aux antibiotiques sont aussi responsables de sérieuses infections émergentes dans des contextes hors mucoviscidose, à la fois dans des conditions intra et extra-hospitalières. Burkholderia cenocepacia, l’une des espèces les plus répandues et isolées chez les patients, est capable d’échapper à la dégradation par les macrophages de l’hôte en bloquant la maturation des (auto)phagosomes. Nous avons récemment démontré que les macrophages servent de niche essentielle pour la réplication intracellulaire de B. cenocepacia K56-2, et sont nécessaires pour le développement d’une réponse pro-inflammatoire aiguë et fatale dans des larves de poisson zèbre. Cette étude exploite d’autant plus le modèle du poisson zèbre pour mieux comprendre quels sont les facteurs bactériens et de l’hôte qui sont impliqués dans la différence entre infection aiguë et persistante, et dans la transition entre ces deux phases infectieuses.ShvR est un régulateur transcriptionnel appartenant aux LTTRs (“LysR-Type Transcriptional Regulators”) chez B. cenocepacia K56-2. Il a été démontré dans le modèle d’infection pulmonaire chez le rat, que ShvR a un rôle important dans l’induction de la réponse pro-inflammatoire, mais pas dans les infections persistantes. Pour cette étude nous utilisons une approche bioinformatique, le modèle du poisson zèbre et des études transcriptomiques afin d’obtenir plus d’informations sur le rôle de ShvR dans la virulence et dans la transition entre infection persistante et réponses pro-inflammatoires. Nos données bioinformatiques suggèrent que le gène shvR s’est adapté par évolution divergente, et a été perdu dans une sous-classe du Bcc. Grâce au modèle du poisson zèbre, nous avons démontré que ShvR n’est pas essentiel pour les stades intra-macrophagiques, mais qu’il est requis pour la dissémination de B. cenocepacia K56-2 des macrophages et pour le développement d’une réponse pro-inflammatoire fatale. Le profile persistant de l’infection a été confirmé par l’analyse du transcriptome de l’hôte, donnant plus d’informations sur les différentes réponses de l’hôte envers les infections par des mutants comparées à la souche sauvage. Le travail de cette thèse a contribué non seulement à une meilleure compréhension du rôle de ShvR et aux gènes cibles régulés par ce dernier qui joue un rôle important dans les infections aiguës, mais également à établir de nouvelles pistes pour développer de nouvelles stratégies thérapeutiques luttant contre les infections par les bactéries appartenant au complexe Bcc. / Bacteria belonging to the Burkholderia cepacia complex (Bcc) are opportunistic pathogens with an intracellular life style. Pulmonary infections with these bacteria significantly worsen clinical outcome for cystic fibrosis (CF) patients. Chronic infections with recurrent acute exacerbations deteriorate lung function with sometimes fatal necrotizing pneumonia and septicaemia (Cepacia Syndrome). These intrinsically multi resistant bacteria are also emerging as the culprit of serious infections in non-CF settings, both in- and outside the hospital. B. cenocepacia, one of the more prevalent species in the complex, is able to avoid degradation by host macrophages by arresting (auto)phagosome maturation. We have recently shown that macrophages provide a critical site for intracellular replication of B. cenocepacia K56-2 and development of acute fatal pro-inflammatory infection in zebrafish larvae. This study further explores the zebrafish infection model to better understand bacterial and host factors involved in the difference between persistent and acute infection, and the transition between these stages.ShvR, a LysR-type transcriptional regulator of B. cenocepacia K56-2, has been shown to play an important role in the induction of pro-inflammatory responses in a rat lung infection model, but not in persistent infection. We used bioinformatics, the zebrafish infection model, and host transcriptome profiling to gain more insight into the role of ShvR in virulence, and in transition between persistent and pro-inflammatory responses. Our bioinformatics study suggests that shvR has adapted by divergent evolution, and has been lost in a subclade of the Bcc. Using the zebrafish embryo model, we demonstrate that ShvR is not important for intramacrophage stages, but is required for dissemination of B. cenocepacia K56-2 from infected macrophages and the development of pro-inflammatory fatal disease. The persistent character of the infection was confirmed by host transcriptomic analysis, giving insight into the differential host response towards the mutant compared to wildtype infection. This thesis contributes to a better understanding of the role of ShvR and its possible target genes that play an important role in acute infection and to future perspectives of development of new targets for the treatment of Bcc infections.

Burkholderia pseudomallei is an opportunistic soil pathogen that causes melioidosis, a life-threatening human disease prevalent in Southeast Asia, northern Australia, the Middle East, Africa, and South America. The organism also causes disease in plants and animals. Persons with severe melioidosis usually die of septicemia. Relatively little is known regarding the virulence mechanisms of B. pseudomallei; however, several putative virulence determinants have been identified. The organism is able to invade and replicate within phagocytic cells and is particularly pathogenic in males with diabetes mellitus. B. thailandensis is closely related to B. pseudomallei, but is not pathogenic. This study examines various in vitro monocyte / macrophage infection models used to study innate immune responses to B. pseudomallei. Several monocyte and macrophage models showed little or no significant differences between proinflammatory cytokines secreted in response to infection with B. pseudomallei and B. thailandensis. Peripheral blood monocytes from diabetic males produced lower normalized levels of proinflammatory cytokines IL-1α, IL-1β, IL-6, and IL-8 than monocytes from healthy males in response to infection with B. pseudomallei, B. thailandensis, and E. coli. Surprisingly, normalized levels of secreted IL-1β from B. pseudomallei-infected monocytes from diabetic females were higher than levels from healthy females. The results revealed a significant interactive effect of gender and diabetic state on peripheral blood monocyte secretion of IL-1β (p = 0.0370) and IL-8 (p = 0.0390), as well as a significant interactive effect of diabetic state and type of infectious agent on peripheral blood monocyte secretion of IL-1α (p=0.0210) and IL-6 (p=0.0204). These results may help explain why diabetic males are unusually susceptible to infection with B. pseudomallei.

No description available.

The bacterium Burkholderia pseudomallei causes the disease melioidosis, a significant public health threat in endemic regions and is a potential biowarfare agent. Treatment of melioidosis is intensive and prolonged and there is no licensed vaccine to protect against it. The aim of this study was to characterise novel targets for antimicrobials to improve treatment of melioidosis. A holistic down selection process was undertaken in order to identify a range of possible novel and exploitable antimicrobial targets in Burkholderia pseudomallei. Four targets: FtsA, FtsZ, MraW and TonB were selected for characterisation by mutagenesis study. FtsA and FtsZ are early effectors of cell division and are considered potential antimicrobial drug targets in other pathogenic bacteria. Genes for both were shown likely to be essential for viability in Burkholderia pseudomallei, following attempted deletion of the genes, thus confirming their potential for drug targeting for treatment of melioidosis. MraW, a highly conserved methyltransferase, and TonB, the energiser for high affinity iron uptake in Gram negative bacteria, were also selected for characterisation as antimicrobial targets. In-frame deletions of the genes encoding these targets were constructed in B. pseudomallei K96243. In order to determine the roles played by MraW and TonB during infection, these mutants were characterised in several models of Burkholderia pseudomallei infection. Deletion of mraW rendered the bacteria non-motile and led to attenuation during infection of Balb/C mice. A small growth defect was seen early during infection of macrophages by this mutant, whilst no attenuation was seen on deletion of mraW in Galleria mellonella. Burkholderia pseudomallei ΔtonB required free iron supplementation for growth. This mutant had an improved ability to invade murine macrophages, though the mutant was attenuated in both Galleria mellonella and Balb/C mice. Attenuation of both mutants in a mammalian model of infection, support the strategy to target either of these proteins as novel targets for inhibition with small molecules during Burkholderia pseudomallei infection. However, an improved ability to infect macrophages by Burkholderia pseudomallei ΔtonB and non-complementation of this mutant by iron supplementation to Galleria mellonella suggests additional roles to iron uptake alone for TonB in Burkholderia pseudomallei, such as bacterial iron sensing and signalling.

A areia de fundição aglomerada com a resina fenólica se transforma num resíduo perigoso após o seu uso na indústria metalúrgica. O fenol, o meta-cresol e orto-cresol foram os principais compostos encontrados na areia de fundição. O presente trabalho tem por objetivo estudar a capacidade de degradação bacteriana do fenol, do meta-cresol e do orto-cresol. Para tanto foi isolada uma cepa proveniente de um resíduo de extração de petróleo tendo sido identificada pelo MALDI-Biotyper como sendo do gênero Burkholderia . Foi realizado o processo de ativação e crescimento bacteriano em pH 6,5, 180 rpm, 28°C e meio de cultura com mínimo de nutrientes, tendo como fonte de carbono areia de fundição contaminada com a resina fenólica. Durante os ensaios foram estudados o crescimento da bactéria bem como a degradação dos compostos fenólicos citados neste texto. A quantificação do fenol, meta-cresol e orto-cresol livres foram determinadas pelo método de cromatografia líquida de alta performance (HPLC - High Performance Liquid Chromatography ). A taxa de degradação para as três substâncias foi de 100%. / The casting sand agglomerated with the phenolic resin becomes a hazardous waste after its use in the metallurgical industry. The main compounds found in sand are phenol and its derivatives ortho-cresol and meta-cresol. The present work aims to study the bacterial degradability of the phenolic compounds present in the foundry sand. A strain from na oil extraction residue was isolated and identified by MALDI-Biotyper as Burkholderia diffusa. It was carried out the process of bacterial activation and growth at pH 6.5, 180rpm of agitation, temperature of 28°C and culture médium with minimum nutrients, using phenolic sand as the only source of carbon. During the tests the growth of the bacterium as well as the degradation of the phenolic compounds were studied. Quantification of free phenol, meta-cresol and ortho-cresol was determined by the high performance liquid chromatography (HPLC) method. The degradation rate for the three substances was 100%.

Burkholderia pseudomallei is the aetiological agent of melioidosis and a potential bioterror threat. Infections are difficult to treat due to extensive antibiotic resistance and there is no prophylactic vaccine available. Studies have shown that the capsular polysaccharide (CPS) of B. pseudomallei is a virulence factor, immunogen and candidate antigen for a glycoconjugate vaccine. However, polysaccharides are complex to synthesise. One approach is to genetically engineer Escherichia coli to express the CPS; however, previous attempts at cloning the CPS coding locus from B. pseudomallei into E. coli were unsuccessful. This project proposes to clone only the essential genes from B. pseudomallei and to use native E. coli mechanisms to complete CPS synthesis. This would contribute to development of a new platform for the expression of any bespoke polysaccharide in E. coli. Six biosynthetic genes for the nucleotide sugar precursor were successfully expressed in E. coli. The structure of the precursor was verified by mass spectrometry. Precursor synthesis was also performed in an in vitro microfluidics system. This minimised the quantity of substrates and enzymes required, in preparation for the characterisation of glycosyltransferases required for CPS assembly. A novel assay for characterising glycosyltransferase activity was also developed, as current available options are prohibitively expensive and require significant quantities of glycosyltransferase which are difficult to purify. Finally, plasmids for the expression of additional glycosyltransferases to link the nascent B. pseudomallei CPS to truncated polysaccharides in E. coli were constructed. The aim of this project was to contribute to the development of a platform for the expression of bespoke polysaccharides in E. coli. The CPS of B. pseudomallei was chosen as the model polysaccharide as it has a simple structure and its manufacture is desirable for use in a vaccine against melioidosis.

Melioidosis, caused by the environmental Gram negative bacillus Burkholderia pseudomallei, is an emerging infectious disease affecting both animals and humans. B. pseudomallei has the ability to enter the host cell and escape from the phagosome. Once in the cytoplasm, the pathogen proliferates and expresses a virulence-associated protein known as BimA which polymerises cellular actin at the pole of the bacterium to promote its movement inter- and intracellularly, a process known as actin-based motility. This actin-based motility is also used as a strategy to evade host immune responses and survive intracellularly. In the first part of the thesis, we demonstrate that a B. pseudomallei ΔbimA mutant displays impaired intracellular survival compared to the isogenic parent strain in BALB/C bone-marrow derived macrophages (BMDMs), notably at later time points post-infection. Macrophages are the key innate immune cells that control B. pseudomallei in vivo and in vitro, and BALB/C mice provide an excellent model of acute human melioidosis. We also have determined that in BMDMs, the ΔbimA mutant is able to escape from the phagosome and enters the cytosol where it is unable to form actin tails. We used targeted, hypothesis-driven experiments to identify potential cell-autonomous innate mechanism/s of killing the mutant. First, we speculated that BimA mediates escape from autophagy. However our studies, including LC3-conversion assays, and bacterial co-localisation studies, failed to demonstrate a role for autophagy in clearance of the ΔbimA mutant from infected BMDMs. In the second part of this thesis, we investigated the role of Toll-like Receptors (TLR) in recognition and elimination of B. pseudomallei. MyD88 (Myeloid differentiation primary-response gene 88) and TRIF (TIR-domain-containing adaptor protein inducing IFNβ) are the main adaptor proteins involved in TLR signalling. We utilised the gene silencing technique using short interfering RNAs (siRNAs) to knockdown MyD88 transcript, and in a separate experiment used MyD88- or TRIF-blocking peptides. In addition, we investigated the involvement of canonical and non-canonical inflammasome pathways in cell-autonomous immunity of the BMDMs. However, none of these pathways were shown to be involved in clearance of the ΔbimA mutant from infected BMDMs. Finally we took an unbiased approach by microarray to characterise the global host transcriptome in BALB/C BMDMs upon B. pseudomallei infection, and to identify specific responses to the ΔbimA mutant. Analyses performed at the gene level revealed that several interferon signalling-related pathways are activated in cells infected with either the WT or ΔbimA mutant strains. A number of other pro-inflammatory mediators that are commonly seen in general inflammatory infections, such as IL-1α, IL-1β, IL-12β, and IL-6, were also upregulated. Interestingly, the cytoplasmic RNA sensors RIG-1 and MDA-5, thought primarily to be involved in the detection of RNA viruses, were also induced upon B. pseudomallei infection. Very few pathways were associated with a specific macrophage response to the ΔbimA mutant, indicating that an as yet undescribed pathway may play a role in sensing and eliminating the ΔbimA mutant. We conclude that actin-based motility mediates escape of B. pseudomallei from macrophage intracellular killing through a novel pathway which has yet to be unravelled.