No description available.

Recent studies into the stringent response and the discovery of a number of RNA polymerase binding proteins suggests that the model for bacterial transcription initiation in Actinobacteria may differ from that in Escherichia coli. In E. coli, the alarmone ppGpp, together with DksA, binds to RNA polymerase to elicit the stringent response. However, the ppGpp binding site on RNA polymerase is not conserved in S. coelicolor, although the organism possesses a DksA homologue. Deletion of DksA did not affect the growth and development of S. coelicolor, although its overexpression stimulated antibiotic production. Evidence is presented that suggests that this occurs through binding to the RNA polymerase secondary channel. The biological role of this protein remains unknown. CarD and RbpA are two RNA polymerase­‐binding proteins present in all Actinobacteria, including S. coelicolor and M. tuberculosis. Both proteins are critical for growth and have been identified as transcriptional activators from σHrdB­‐dependent promoters in vitro. Here it was demonstrated that CarD and RbpA activate transcription from rRNA promoters with a poorly conserved ­‐35 element. Surprisingly it was also found that both proteins can inhibit transcription from synthetic promoters with highly conserved ­‐35 elements. Chromatin immunoprecipitation followed by high throughput sequencing (ChIP­‐seq) experiments revealed that CarD and RbpA are found exclusively at promoter regions. RbpA is localised only at promoters recognised by σHrdB, whereas CarD also co‐localises with the alternative sigma factor σR during oxidative stress indicating that it lacks RNA polymerase holoenzyme specificity. The sigma specificity of RbpA was tested by the generation of sigma mutants that were defective in binding. In vivo, in vitro and ChIP­‐seq data presented in this study suggest that CarD and RbpA have an overlapping role in transcription initiation at σHrdB­‐dependent promoters in S. coelicolor.

Yersinia pestis, the aetiological agent of plague, is responsible for a disease that has killed over 200 million people throughout history and generated three pandemics. This bacterium's terrible success in causing disease is owed greatly to the virulence factors it expresses. Two of these factors are V antigen (LcrV) and F1 antigen (Caf1), both of which are two major antigens which the immune system produces antibodies against. V antigen is already known to have vital roles in Y. pestis gene expression and translocating other virulence factors into the host cells as well as having some immunosuppressive effects while F1 antigen is better known for possessing an antiphagocytic effect. The effects that these two antigens have in modulating the innate immune system of Mono Mac 6 cells were studied, such as modulation of expression of pattern recognition receptors (PRRs), in particular Toll-like receptors (TLRs), activation of NF-κB and secretion of cytokines, particularly those involved in inflammatory responses, as well as localising where in the cell these antigens target to. It was demonstrated that both V and F1 antigens possess immunosuppressive abilities, such as downregulation of TLRs as well as inhibitition of NF-κB activation and suppression of secretion of the cytokines TNF-α, IL-6 and IL-10. Furthermore, stimulation with only either V or F1 antigens can upregulate expression of the scavenger receptor CD36 and are capable of inducing secretion of the anti-inflammatory cytokine IL-10. V and F1 antigens were found to localise in the Golgi apparatus 30 minutes after stimulation and it was also determined that these antigens interfere with the signalling molecule MyD88.

Heritable bacterial symbionts are astonishingly common in insects, yet relatively little is known about how heritable symbionts influence the biology of social insects such as ants, bees, wasps and termites. In this thesis I investigate various aspects of the biology of heritable symbionts in social insects, principally focusing on the relationship between ants, the largest group of social insects, and the symbiont Wolbachia, the archetypal reproductive parasite. In Chapter 1, I begin by reviewing the biology of Wolbachia. In Chapter 2, I show that the sex, caste and size of an individual's colony determine the likelihood that it is infected with Wolbachia, and I provide correlational evidence that Wolbachia provides small increases in colony productivity in the ant Temnothorax crassispinus. In Chapter 3, I combine colony censuses and antibiotic treatment experiments, finding that Wolbachia neither distorts host sex ratios nor causes strong female mortality type mating incompatibilities in the ant Myrmica scabrinodis. In Chapter 4, I critically evaluate the theory that heritable symbionts should evolve to manipulate caste-fate in social insects, outlining three distinct evolutionary scenarios under which this might occur. In Chapter 5, I provide evidence for negative interactions between Wolbachia and both Spiroplasma and Arsenophonus in M. scabrinodis hosts, and I show that multiple unrelated strains of both Wolbachia and Spiroplasma occur across the Palaearctic. In Chapter 6, I show that one of two strains of Wolbachia infecting the ant Monomorium pharaonis was acquired by hybrid introgression. In Chapter 7, I find that ant species with limited queen dispersal are almost twice as likely to be infected with Wolbachia relative to other ant species, supporting the hypothesis that population structure influences the invasion ability of Wolbachia. Finally, in Chapter 8, I discuss the broader significance of my findings.