Zugl.: Frankfurt (Oder), Univ., Diss., 2003

Bacteria of the genus Bartonella infect the red blood cells of a wide range of wild and domestic mammals and are transmitted between hosts by blood-sucking insects. Although most Bartonella infections are asymptomatic, the genus contains several human pathogens. In this work, host adaptation and host switches in Bartonella have been studied from a genomic perspective, with special focus on the acquisition and evolution of genes involved in host interactions. As part of this study, the complete genome of B. grahamii isolated from a Swedish wood mouse was sequenced. A genus-wide comparison revealed that rodent-associated Bartonella species, which have rarely been associated with human disease, have the largest genomes and the largest number of host-adaptability genes. Analysis of known and putative genes for host interactions identified several families of autotransporters as horizontally transferred to the Bartonella ancestor, with a possible role both during early host adaptation and subsequent host shifts. In B. grahamii, the association of a gene transfer agent (GTA) and phage-derived run-off replication of a large genomic segment was demonstrated for the first time. Among all acquisitions to the Bartonella ancestor, the only well conserved gene clusters are those that encode the GTA and contain the origin of the run-off replication. This conservation, along with a high density of host-adaptability genes in the amplified region suggest that the GTA provides a strong selective advantage, possibly by increasing recombination frequencies of host-adaptability genes, thereby facilitating evasion of the host immune system and colonization of new hosts. B. grahamii displays stronger geographic pattern and higher recombination frequencies than the cat-associated B. henselae, probably caused by different lifestyles and/or population sizes of the hosts. The genomic diversity of B. grahamii is markedly lower in Europe and North America than in Asia, possibly an effect of reduced host variability in these areas following the latest ice age.

Microsporidia are a unique phylum of ubiquitous fungal pathogens that are able to infect a wide variety of hosts, including economically and ecologically important organisms. Recently, global declines of the Western honeybee (Apis mellifera) have been associated with infections of the microsporidian pathogen Nosema ceranae. This species was originally described in the Asiatic honeybee (A. cerana), and its identification in global A. mellifera hives could result from a recent host transfer. Recent genome studies have found that global populations of this parasite from A. mellifera hives are polyploid and that humans may have fueled their global expansion. In this thesis, I investigate the genetic diversity of N. ceranae populations from within their native range (Thailand) and among different hosts (A. mellifera, A. cerana), putting them in context with other previously sequenced global populations. Using both PCR and genome-based methods, my findings reveal that Thai populations of N. ceranae exhibit interesting genetic differences from other global pathogen populations but also have some similarities. Thai N. ceranae populations share many single nucleotide polymorphisms (SNPs) with other global populations and appear to be clonal. However, in stark contrast with previous studies, these populations carry many SNPs not found in other global populations of this parasite, indicating that these populations have evolved in their current geographic location for some time. This genome analysis also indicates the potential presence of diploidy within Thai populations of N. ceranae and possible host-specific loss of heterozygosity. Overall, my findings begin to reveal interesting patterns of genetic diversity in N. ceranae populations that bring us one step closer to understanding the biology and genetics of this important honeybee pathogen.

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No description available.

El treball presentat en aquesta tesi és un estudi de la diversitat genètica en un conjunt de gens implicats en funcions neurològiques ("Gens cerebrals"). Hom ha examinat vint-i-dos gens implicats en els sistemes de neurotransmissió dopaminèrgic, serotoninèrgic i glutamatèrgic. L'objectiu de l'estudi té dos vessants: per una banda l'anàlisi de la diversitat genètica en un conjunt de gens implicats en malaltia humana, en aquest cas en malaltia psiquiàtrica, en poblacions humanes mundials, amb la intenció d'assentar les bases per propers esforços de mapatge genètic; i per altra banda analitzar la diversitat genètica en aquest conjunt de gens per tal de descobrir evidències d'esdeveniments històrics, incloent possibles evidències de selecció. / The work presented in this thesis is a study of the genetic variation in a set of genes related to neurological function ('Brain genes'). Twenty two genes are examined, all of which are involved in either the Dopaminergic, Serotonergic or the Glutamatergic systems of neurotransmission.The objective of the study has two aspects: on the one hand the analysis of genetic variation in a set of genes which are implicated in human disease, in this case psychiatric disease, across global human populations, towards the end of providing some new insight for gene mapping efforts, and on the other hand the study of genetic variation in this set of genes may reveal traces of the population history events undergone, including possible evidence for selection.