Alteration of genetic content and gene expression modulate the pathogenic potential of Campylobacter jejuni

A leading cause of bacterial gastroenteritis worldwide, Campylobacter jejuni is responsible for as many as 2.5 million reported cases per year in the United States of America alone. Campylobacter is a flagellated, spiral shaped, Gram-negative bacterium. The development of new genetic tools and availability of the C. jejuni genome sequence has accelerated the progress made in the field of Campylobacter pathogenesis in the past decade. Although a number of virulence determinants have been identified, to date their role in the ability of Campylobacter to cause disease remains unknown. The research presented in this dissertation highlights two distinct features by which C. jejuni is able to toggle between a virulent and an avirulent state. First, C. jejuni is able to alter its genetic content to exhibit variable motility phenotype. It is proposed that alternating between a motile and a non-motile state helps Campylobacter switch from its commensal lifestyle in one host to an invasive lifestyle in the other. The data presented in Chapter 2 indicate that the differences observed in the virulence phenotype of two poultry isolates CS and S2B were a result of a point mutation in the flgR and rpoN genes, respectively. Proteins encoded by both these genes are essential for flagellar biosynthesis, thus mutations in these genes rendered the organism non-motile and hence avirulent. Second, Campylobacter alters its virulence potential by modulating its gene expression in response to an environmental stimulus. To adapt and survive within the intestinal tract Campylobacter must alter its genes expression in response to the varied in vivo conditions encountered including exposure to bile. The data presented in chapter three demonstrate that culture in the presence of bile salts enhances the virulence potential of Campylobacter. When cultured in the presence of the bile salt sodium deoxycholate, C. jejuni undergoes a synthetic response characterized by the upregulation of genes known to play a role in Campylobacter pathogenesis. Taken together, the data presented show that Campylobacter is able to vary its virulence potential by altering its genetic content and gene expression

The Bimodal Lifestyle of Intracellular Salmonella in Epithelial Cells: Replication in the Cytosol Obscures Defects in Vacuolar Replication

Salmonella enterica serovar Typhimurium invades and proliferates within epithelial cells. Intracellular bacteria replicate within a membrane bound vacuole known as the Salmonella containing vacuole. However, this bacterium can also replicate efficiently in the cytosol of epithelial cells and net intracellular growth is a product of both vacuolar and cytosolic replication. Here we have used semi-quantitative single-cell analyses to investigate the contribution of each of these replicative niches to intracellular proliferation in cultured epithelial cells. We show that cytosolic replication can account for the majority of net replication even though it occurs in less than 20% of infected cells. Consequently, assays for net growth in a population of infected cells, for example by recovery of colony forming units, are not good indicators of vacuolar proliferation. We also show that the Salmonella Type III Secretion System 2, which is required for SCV biogenesis, is not required for cytosolic replication. Altogether this study illustrates the value of single cell analyses when studying intracellular pathogens

High temperature magnetic ordering in La2RuO5

Magnetic susceptibility, heat capacity and electrical resistivity measurements have been carried out on a new ruthenate, La2RuO5 (monoclinic, space group P21/c) which reveal that this compound is a magnetic semiconductor with a high magnetic ordering temperature of 170K. The entropy associated with the magnetic transition is 8.3 J/mole-K -close to that expected for the low spin (S=1) state of Ru4+ ions. The low temperatures specific heat coefficient g is found to be nearly zero consistent with the semiconducting nature of the compound. The magnetic ordering temperature of La2RuO5 is comparable to the highest known Curie temperature of another ruthenate, namely, metallic SrRuO3, and in both these compounds the nominal charge state of Ru is 4+.Comment: 16 pages, 6 figures, To be published in Solid State Communication

AGN feedback with the Square Kilometer Array (SKA) and implications for cluster physics and cosmology

AGN feedback is regarded as an important non-gravitational process in galaxy clusters, providing useful constraints on large-scale structure formation. It modifies the structure and energetics of the intra-cluster medium (ICM) and hence its understanding is crucially needed in order to use clusters as high precision cosmological probes. In this context, particularly keeping in mind the upcoming high quality radio data expected from radio surveys like SKA with its higher sensitivity, high spatial and spectral resolutions, we review our current understanding of AGN feedback, its cosmological implications and the impact that SKA can have in revolutionizing our understanding of AGN feedback in large-scale structures. Recent developments regarding the AGN outbursts and its possible contribution to excess entropy in the hot atmospheres of groups and clusters, its correlation with the feedback energy in ICM, quenching of cooling flows and the possible connection between cool core clusters and radio mini-halos, are discussed. We describe current major issues regarding modeling of AGN feedback and its impact on the surrounding medium. With regard to the future of AGN feedback studies, we examine the possible breakthroughs that can be expected from SKA observations. In the context of cluster cosmology, for example, we point out the importance of SKA observations for cluster mass calibration by noting that most of $z>1$ clusters discovered by eROSITA X-ray mission can be expected to be followed up through a 1000 hour SKA-1 mid programme. Moreover, approximately $1000$ radio mini halos and $\sim 2500$ radio halos at $z<0.6$ can be potentially detected by SKA1 and SKA2 and used as tracers of galaxy clusters and determination of cluster selection function.Comment: 14 pages, 10 figures, Review article accepted in Journal of Astrophysics and Astronomy (JOAA

Salmonella – At Home in the Host Cell

The Gram-negative bacterium Salmonella enterica has developed an array of sophisticated tools to manipulate the host cell and establish an intracellular niche, for successful propagation as a facultative intracellular pathogen. While Salmonella exerts diverse effects on its host cell, only the cell biology of the classic “trigger”-mediated invasion process and the subsequent development of the Salmonella-containing vacuole have been investigated extensively. These processes are dependent on cohorts of effector proteins translocated into host cells by two type III secretion systems (T3SS), although T3SS-independent mechanisms of entry may be important for invasion of certain host cell types. Recent studies into the intracellular lifestyle of Salmonella have provided new insights into the mechanisms used by this pathogen to modulate its intracellular environment. Here we discuss current knowledge of Salmonella-host interactions including invasion and establishment of an intracellular niche within the host

Invasin-functionalized liposome nanocarriers improve the intracellular delivery of anti-infective drugs

Intracellular infections caused by invasive pathogens continue to prove difficult to combat, due in part to the commonly poor membrane permeability of anti-infective drugs. The aim of this study was to improve the intracellular delivery of one such poorly permeable (but broad-spectrum) anti-infective, gentamicin. Gentamicin was encapsulated into liposomal nanocarriers which were then surface functionalized with InvA497, a bacteria-derived invasion protein. Treatment of HEp-2 cells infected with the enteroinvasive bacteria Yersinia pseudotuberculosis or Salmonella enterica with gentamicincontaining, InvA497-functionalized liposomes resulted in a significantly greater reduction in infection load than treatment with non-functionalized liposomes, indicating that such a bacteriomimetic nanocarrier was not only able to promote successful cellular uptake of gentamicin but was also able to mediate anti-infective drug delivery to both cell cytoplasm and intracellular compartments. The developed InvA497-functionalized liposomal nanocarrier therefore holds great promise as a strategy for improving the therapy of intracellular infections

Network embeddedness and new product development in the biopharmaceutical industry: The moderating role of open innovation flow

This paper explores the role of centrality and structural holes positions on the likelihood to develop new products and the moderating role of the open innovation flow, a measure of the net knowledge flow crossing the firm's boundaries, on the aforementioned relation. We argue that network positions provide the information content to the firm, whilst open innovation flow describes how the firm uses such content, thus the combination of these two concepts has a significant impact on new product development. We test the theoretical framework on a large sample of 544 public companies and data from 1758 agreements among 1890 bio-pharmaceutical firms through the period 2006-2010. Our results show that being centrally located in the network positively affects the new product development process, while having a structural holes position has no effect on the aforementioned performance. However, the interaction of the two network positions with the open innovation flow has a positive impact on the likelihood to develop new products

The interaction between inter-firm and interlocking directorate networks on firm's new product development outcomes

This paper explores the interaction between a prominent board of directors and the network of inter-firm relationships on new product development. Specifically, we posit a positive interaction effect between a prominent board and the inter-firm network and structural holes positions on the number of new products developed by the firm. We test the theoretical framework on a sample of 1758 agreements among 1890 biopharmaceutical firms over the period 2006–2010. We find that by filtering, complementing and legitimizing information coming from the inter-firm network, a prominent interlocking directorate network can improve the inter-firm network's effects on new product development. We discuss important implications for how inter-personal networks (such as the board interlock directorate network) help to develop the effectiveness of inter-firm relationship networks in achieving new product development outcomes

Nutritional and Metabolic Requirements for the Infection of HeLa Cells by Salmonella enterica Serovar Typhimurium

Salmonella is the causative agent of a spectrum of human and animal diseases ranging from gastroenteritis to typhoid fever. It is a food - and water - borne pathogen and infects via ingestion followed by invasion of intestinal epithelial cells and phagocytic cells. In this study we employed a mutational approach to define the nutrients and metabolic pathways required by Salmonella enterica serovar Typhimurium during infection of a human epithelial cell line (HeLa). We deleted the key glycolytic genes, pfkA and pfkB to show that S. Typhimurium utilizes glycolysis for replication within HeLa cells; however, glycolysis was not absolutely essential for intracellular replication. Using S. Typhimurium strains deleted for genes encoding components of the phosphotransferase system and glucose transport, we show that glucose is a major substrate required for the intracellular replication of S. Typhimurium in HeLa cells. We also deleted genes encoding enzymes involved in the utilization of gluconeogenic substrates and the glyoxylate shunt and show that neither of these pathways were required for intracellular replication of S. Typhimurium within HeLa cells

Predation on Multiple Trophic Levels Shapes the Evolution of Pathogen Virulence

The pathogen virulence is traditionally thought to co-evolve as a result of reciprocal selection with its host organism. In natural communities, pathogens and hosts are typically embedded within a web of interactions with other species, which could affect indirectly the pathogen virulence and host immunity through trade-offs. Here we show that selection by predation can affect both pathogen virulence and host immune defence. Exposing opportunistic bacterial pathogen Serratia marcescens to predation by protozoan Tetrahymena thermophila decreased its virulence when measured as host moth Parasemia plantaginis survival. This was probably because the bacterial anti-predatory traits were traded off with bacterial virulence factors, such as motility or resource use efficiency. However, the host survival depended also on its allocation to warning signal that is used against avian predation. When infected with most virulent ancestral bacterial strain, host larvae with a small warning signal survived better than those with an effective large signal. This suggests that larval immune defence could be traded off with effective defence against bird predators. However, the signal size had no effect on larval survival when less virulent control or evolved strains were used for infection suggesting that anti-predatory defence against avian predators, might be less constrained when the invading pathogen is rather low in virulence. Our results demonstrate that predation can be important indirect driver of the evolution of both pathogen virulence and host immunity in communities with multiple species interactions. Thus, the pathogen virulence should be viewed as a result of both past evolutionary history, and current ecological interactions