Selfish genetic elements can distort the sex ratios of their hosts by increasing their own transmission to the next generation in a non-mendelian fashion. These elements can be either nuclear genes on a sex chromosome or cytoplasmically inherited microbes, and achieve an increased transmission by manipulating gametogenesis or host reproduction. Often these selfish elements benefit from a female biased population (for example heritable microbes are passed on maternally in the egg cytoplasm), while non-selfish, autosomal genes are selected to produce a balanced sex ratio. These differing reproductive strategies cause a genetic conflict that results in an “evolutionary arms race” that can promote the evolutionary change of sex determination systems. In this thesis, I investigate an extreme sex ratio distortion in a species of booklouse, Liposcelis sp. This species contains two distinct female types, one of which carries a maternally transmitted selfish genetic element that results in exclusively female offspring being produced. Recently, a candidate for the sex ratio distortion was identified as a horizontally transferred bacterial gene, that we have called Odile, and that is present in the genome of the (distorter) female carrying the distorting element. The gene originates from the endosymbiotic bacterium Wolbachia that is well known for its ability to distort the sex ratio of its hosts. I investigated this horizontal gene transfer event and attempt to characterize Odile. I provide evidence that this Wolbachia gene has been integrated into the genome of the distorter females and is not a bacterial contaminant. I found that the Odile gene has been duplicated and may have been horizontally transferred from Wolbachia independently to at least three other insect genomes. Additionally, I found that Odile is transcribed at low levels in a life-stage specific manner that is suggestive of a role in development. Additionally, I looked into male mate choice in this species as one aspect of the persistence of the distorting element. I found that male Liposcelis sp. do not discriminate between the two female types and do not spend more time mating with one female type over the other. These results contribute to ongoing research into the extreme sex ratio distortion found in this species and the candidate gene that may be the cause. Selfish genetic elements are an important driver of sex determination evolution, and Liposcelis sp. provides a unique and exciting system to investigate the implications of selfish elements in a genome further. / Graduate / 2019-12-17

Made available in DSpace on 2014-06-11T19:23:02Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-17Bitstream added on 2014-06-13T19:28:52Z : No. of bitstreams: 1 santos_vp_me_rcla.pdf: 692384 bytes, checksum: 87577700198a680d7662c5fe0990efe7 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / As cianobactérias apresentam uma ampla variabilidade fenotípica e ecológica. Porém, esta variabilidade, muitas vezes, não corresponde à sua diversidade genética. Assim, o uso de marcadores moleculares é fundamental para os estudos de filogenia neste grupo. Entretanto, a filogenia molecular enfrenta um desafio na seleção dos marcadores devido à ocorrência relativamente frequente da transferência de genes de forma lateral entre os procariotos. Em cianobactérias os marcadores dos espaçadores dos genes ribossomais (16S-23S-ITS rDNA) e do operon da ficocianina (PC-IGS) estão entre os mais utilizados nestes estudos. Contudo, alguns trabalhos sugerem que o PC-IGS possa ter sito transferido lateralmente em sua história evolutiva. A identificação de morfoespécies dos gêneros Microcystis e Geitlerinema é baseada em caracteres morfológicos que em geral não correspondem à sua variabilidade genética. Com o objetivo de investigar a transferência lateral do operon da ficocianina em Geitlerinema e Microcystis, foram obtidas e comparadas árvores filogenéticas de ambas espécies baseadas nos marcadores PC-IGS e 16S-23S-ITS rDNA. As topologias das árvores obtidas para ambos os marcadores foram muito semelhantes e indicaram que o PC-IGS é estável e indicado para os estudos de taxonomia e filogenia de linhagens de Geitlerinema e Microcystis. Assim, hipótese inicial de transferência lateral foi refutada. Algumas linhagens tiveram seu posicionamento divergente entre um marcador e outro, o que ressalta a importância do uso de mais de um marcador em estudos de filogenia. O marcador PC-IGS apresentou melhor desempenho que 16S-23S-ITS rDNA. As árvores filogenéticas de Geitlerinema baseadas em ambos os marcadores indicaram a ocorrência de espécies crípticas dentre as linhagens estudadas e corroboraram que G. amphibium e G. unigranulatum devem ser consideradas sinonímias... / Cyanobacteria show a wide phenotypic and ecological variability, but frequently this variability does not correspond to their genetic variation. Therefore, the use of molecular markes is critical for phylogenetic studies in this group. At the same time, the selection of molecular markers represents a challenge for the molecular phylogeny due to the horizontal gene transfer, witch is a relatively common process among the prokaryotes. In cyanobacteria, makers for the ribosomal genes spacer (16S-23S-ITS rDNA) and for the phycocyanin operon spacer (PC-IGS) are among of the most used for phylogeny. However, some studies suggest that the PC-IGS marker may have been horizontally transferred during its evolutionary history. The identification of the morphospecies from the genus Microcystis and Geitlerinema is based in their morphological characters, but they generally do not correspond to genetic variability. In order to investigate the possibility of horizontal transfer of the phycocyanin operon in Microcystis and Geitlerinema, phylogenetic trees based on the PC-IGS and 16S- 23S-ITS rDNA were generated and compared. The topologies obtained for both markers were very similar, indicating that the PC-IGS marker is stable and suitable for taxonomical and phylogenetic studies in Microcystis and Geitlerinema. Therefore, the initial hypothesis of horizontal transfer was rejected. Some strains were found to have divergent positions between the trees based on the two molecular markes, witch highlights the importance of using more than one marker in phylogenetic studies. The PC-IGS marker performed better than 16S-23SITS rDNA. The Geitlerinema phylogenetic trees based on both markers indicated the occurrence of cryptic species among the strains and corroborated that G. amphibium and G. unigranulatum should be treated as synonyms. The phylogenetic tree based on PC-IGS formed a monophyletic clade... (Complete abstract click electronic access below)

Microsporidia are obligate intracellular pathogens of medical and ecological importance whose genomes have been studied extensively over the last decade. Their parasitic lifestyle has lead them to lose a great number of genes and, thus, biochemical pathways capacities, but these reductive processes have been often offset by the acquisition of several genes by means of horizontal gene transfer (HGT). First, in this thesis, we will describe the complete genomes of Encephalitozoon hellem and Encephalitozoon romaleae. Both species also were found to harbor a number of protein-coding genes absent in other microsporidia, which products assembled complete metabolic pathways. All these genes are functionally related to DNA and folate metabolism, and all appear to have been acquired from HGT events from different eukaryotic and prokaryotic donors. Interestingly in E. romaleae genes involved in de novo synthesis of folate are all pseudogenes, highlighting the transient nature of transferred genes. Secondly, we took a closer look at the ploidy and sexual status of Encephalitozoon cuniculi, a vertebrate pathogen, by mapping Illumina sequence reads against the genomes of four strains of this species. We identified the presence of low level of heterozygosity in all strains investigated; a feature that revealed the diploid nuclear state of the species. This reductive intra-individual genetic diversity could result from the long-term propagation of these strains under laboratory conditions, but we propose that it could also reflect an intrinsic capacity of these vertebrate pathogens to self-reproduce. Overall, the work presented in this thesis resulted in a much greater understanding of the genome evolution of a medically and economically important group of parasites.

For many years, researchers have studied the social lives of bacteria to understand intra- and inter-species interactions. Cell-cell communication, also known as quorum sensing (QS), is used by bacteria to coordinate their behaviour in response to environmental conditions. The QS system in Streptococcus species is well known to regulate competence. Studies show that Streptococcus pneumoniae has two homologous QS systems: 1) the competence (Com) system that regulates competence; and 2) a bacteriocin-like peptide (Blp) system that regulates the production of bacteriocins. Both functions are widespread in the genus. In S. pneumoniae, the Blp QS system shares a common ancestor and has similar features to the Com QS system. However, the evolutionary relationship between these QS systems remains obscure. SUCRE methodology was developed to identify the QS homologous genes in the streptococcal species. SUCRE uses four complementary approaches: homology search, putative gene finding, regulon construction, and evolutionary analysis. The performance of SUCRE was assessed in comparison with other orthology detection methods. SUCRE is precise in identifying the QS homologous genes and has similar performance to OrthoMCL. The QS system structures are found to be conserved across the streptococcal species. A streptococcal species phylogeny was constructed from the ribosomal and tRNA synthetase gene families. Using the QS genes identified from SUCRE and the streptococcal species phylogeny, the study infers the evolution of the QS systems in Streptococcus species. The study shows that the QS systems evolved as a regulon unit. The paralogous relationship between each of the QS systems suggests that duplication has a huge influence on functional divergence of the QS systems in the genus. Although, horizontal gene transfer (HGT) is commonly found in bacteria, little evidence is found to support that the effect of HGT on the functional divergence of the QS systems in this genus. However, the QS regulon genes of the same QS system are found to be non- vertically transferred across species that signifies that the HGT event promotes the sequence variation between these genes.

<div>Antibiotics have been widely used to treat bacterial diseases since the 1940s. However, the benefits offered by antibiotics have gradually faded due to the increased occurrence and frequency of antibiotic resistance. The widespread use of antibiotics has driven selection for resistance in bacteria and is becoming a global problem for human health and the environment. Antibiotic resistance is exacerbated by the ability of bacteria to share their antibiotic resistance genes (ARGs) with other bacteria via horizontal gene transfer (HGT). Many existing studies on HGT of ARGs focused on antibiotic concentrations at or above the minimal inhibitory concentration (MIC), which is the lowest concentration of an antibiotic that prevents visible growth of a bacteria culture. However, knowledge on the development of antibiotic resistance under different stressors at sub-MIC levels is still limited. In addition, carbon nanotubes (CNTs) have been widely studied in environmental, agricultural and biomedical areas due to their unique physical and chemical characteristics, but limited studies have been done to evaluate the effects of CNTs on the spread of ARGs. Electrochemical filtration has been shown to be a cost-effective technique to remove recalcitrant compounds and reduce antibiotic resistance, but limited studies have been done to evaluate the effectiveness of removal of ARGs with electrochemical filtration. Therefore, there is a critical need to evaluate the effects of trace levels of antibiotics and CNTs on the development of antibiotic resistance and electrochemical removal of ARGs. </div><div><br></div><div>The specific research objectives of this study were to evaluate: (1) selective pressure of sub-inhibitory concentrations of antibiotics on the development of antibiotic resistance and HGT, (2) development of antibiotic resistance and HGT under exposure to CNTs and antibiotics, and (3) effectiveness of using an electrochemical MWCNT filter to remove ARGs. </div><div><br></div><div>To evaluate the development of antibiotic resistance exposed to sub-MIC of erythromycin, HGT between environmental donor (<i>E. coli)</i> and pathogenic bacterial recipient (<i>B. cereus</i>) was quantified. The results indicated that extremely low concentration (0.4 ng/L to 4 µg/L) of erythromycin promoted HGT of <i>erm</i>80 gene, which is an erythromycin resistance gene. In addition to traditional culture-based method and quantitative real-time PCR (qPCR), a fluorescence <i>in situ</i> hybridization (FISH) approach was used to detect the occurrence and development of ARGs even the bacteria were in the viable but nonculturable (VBNC) state after treatment of sub-lethal level of erythromycin. Multi-walled carbon nanotubes (MWCNT) was selected as a representative stressor to evaluate the effects on HGT. The results showed that MWCNT enhanced HGT above 1 × MIC, which is the lethal level of erythromycin to recipients, and transfer frequencies of erm80 genes increased up to 101-fold under exposure to 1 × MIC erythromycin and MWCNT as compared to no MWCNT control. However, transfer efficiency of <i>erm</i>80 gene under exposure to sub-MIC of erythromycin was inhibited by MWCNTs. Moreover, transfer of antibiotic resistance plasmids was affected by antibiotics and MWCNTs. Although the concentration of individual stressor was not enough to confer antibiotic selection, effects of both antibiotics above 1 × MIC and MWCNTs could add up and select for antibiotic resistance. The results suggested that CNTs might create additional selective pressure for the spread of ARGs and their effects on HGT should be further investigated. Finally, an electrochemical MWCNT filtration was evaluated to remove genomic DNA and ARGs under the effects of operating conditions, such as pH, phosphate, and NOM. The results showed that the electrochemical MWCNT filtration reactor achieved 79% removal efficiency for genomic DNA and 91% removal efficiency for <i>erm</i>80 genes. The study suggested that electrochemical MWCNT filtration could be a promising technology for the removal of DNA and ARGs.</div><div><br></div><div>Overall, the results improved our understanding of the development of antibiotic resistance and ARGs under various selective pressures. Trace levels of antibiotics promoted the development and spread of ARGs. Conjugative transfer of resistance genes exposed to sub-MIC levels of erythromycin and MWCNTs also contributed to the spread and propagation of ARGs. As antibiotic concentrations detected in natural environment are often in trace levels, the results of this study may improve the understanding of health risks of trace levels of antibiotics and help develop effective mitigation strategies to control the spread of antibiotic resistance. Effective removal of ARGs with electrochemical MWCNT filtration may help the development of cost-effective treatment systems to remove ARGs to protect human health and the environment.</div><div><br></div>

Bacterial diversity has always been associated with micro-evolutionary events such as horizontal gene transfer and DNA mutations. Such events influence the rapid evolution of bacteria as a result of the environmental conditions which they encounter. They further establish beneficial phenotypic effects that allow bacteria to specialize in new habitats. Due to the increase in number of bacterial genomic sequences, studying microbial evolution has been made possible, and the impact of micro-evolution on bacterial diversity is becoming more apparent. To gain biological information from this ever increasing genomic data, a variety of computational tools are required. This thesis therefore, focuses on the development and application of computational approaches to identify genomic regions of divergence which have resulted from horizontal gene transfer or small mutational changes. The first and major part of the thesis describes the application of DNA patterns, termed oligonucleotide signatures to identify horizontally acquired genomic regions in prokaryotes. These DNA patterns are demonstrated to differentiate between signatures of the core genome and those which have been acquired through horizontal transfer events. DNA patterns are further demonstrated to: reveal the distribution patterns of horizontally acquired genomic elements, determine their acquisition periods, and predict their putative donor organisms. The second part of the thesis focuses on the evaluation of modern short read sequence data of geographically unrelated Pseudomonas aeruginosa to study their intraclonal genomic diversity. The work described in the thesis was purely in silico driven and performed at Hannover Medical School and the Bioinformatics and Computation Biology Unit at the University of Pretoria. / Thesis (PhD)--University of Pretoria, 2013. / gm2014 / Biochemistry / unrestricted

The discovery of antibiotics have revolutionized modern medicine, facilitating the treatment of a variety of bacterial infections, enabled surgeries otherwise impossible to perform and increased life expectancy in all countries. However, the rapid development of resistance among microorganisms and the increasing numbers of clinical outbreaks caused by multiresistant bacteria have accelerated the need for new alternatives to antibiotics. Probiotic bacteria armed with defense systems have been studied as potential substitutes of antibiotics. These probiotic competitors can still contribute to the spread of resistance genes among microorganisms through horizontal gene transfer. The aim of this study was to investigate whether constructed CRISPR-Cas9 systems have the potential to protect probiotic bacteria against horizontal transfer of antibiotic resistance genes. Transformation, transduction and conjugation assays in strains carrying or not carrying a plasmid-bourne CRISPR-Cas9 system were performed in order to compare the frequencies of transfer of the most common resistance genes. The transformation and transduction assays demonstrated that the constructed CRISPR-Cas9 system entails a decrease in efficiency of transfer for targeted resistance genes. Moreover, it can be concluded that potentially increasing Cas9 levels by reducing its degradation results in increased prevention of horizontal gene transfer through transformation and transduction. Finally, we state that the CRISPRCas9 system does not result in protection against antibiotic resistance genes entering the cells through conjugation.

Continuous increases in the interest and implementation of wastewater reuse due to intensified water stress has escalated the concerns of emerging contaminants. Among emerging contaminants there are microbial (antibiotic resistance) and chemical (pharmaceuticals) elements which have been shown to survive wastewater treatment. This dissertation aims to mitigate emerging contaminants by means of understanding and/or developing the appropriate disinfection strategies, with the intention to provide knowledge that would facilitate towards safe and sustainable water reuse. The first part of this thesis explored microbial risk component of antibiotic resistance. Antibiotic resistance genes are abundant in treated wastewater, and only pose a risk if taken up by potential pathogens through natural transformation. Our results showed that solar irradiation can double natural transformation rates, mediated by reactive oxygen species generation, which led to upregulation in DNA repair and competence genes in Acinetobacter baylyi ADP1. Treatment with UV-C254 nm irradiation also resulted in upregulation in DNA repair genes, nevertheless we observed a decrease in natural transformation rates. These results imply that direct damage of antibiotic resistance genes (ARG) could inhibit their spread and therefore risk, despite other factors contributing to the contrary. The next chapter in this dissertation postulated that the UV/H2O2 combination would be ideal to treat microbial and chemical emerging contaminants in effluent generated from an anaerobic membrane bioreactor. We demonstrated that at an optimal UV intensity and H2O2 concentration, we were able to achieve a 2 and 6-log reduction of the two antibiotic resistance genes and bacteria and used in this study, respectively, and more than 90% removal of the three pharmaceutical compounds. These observations suggest that UV/H2O2 has great potential in treating effluent with high nitrogen concentrations, preserving the fertilization benefit of AnMBR effluent. Overall, this dissertation revealed the potential of UV-based treatments for treated wastewater intended for reuse. Post-membrane processes effluent allows one to deploy UV-C254 nm to selectively target DNA and therefore ARB and ARG that may be still present in the treated wastewater. At the same time, coupling chemical oxidants with UV-C (i.e., UV AOP) would further enhance the means to simultaneously oxidize and degrade potentially harmful chemical contaminants.

Horizontal gene transfer transforms commensal E. faecalis into multidrug resistance (MDR) opportunistic pathogens causing diseases such as infective endocarditis (IE), septicemia, and urinary tract infections (UTI) (4,1). E. faecalis are among the top three leading causes of hospital-acquired infections and pheromone responsive plasmids (pCF10) are the most extensively characterized conjugative plasmids in E. faecalis infection (2,4). E. faecalis is a potential future public health concern because of the co-occurrence factors of antibiotic resistance and virulence traits (6)Plasmid-free commensal E. faecalis form homogenous biofilms that have a uniform distribution of the bacterial cell and a fluid-like movement (22). The introduction of the pheromone responsive plasmid pCF10 leads to the formation of heterologous rigid structures within the biofilm (22). In the current work, the timeline of biofilm tower formation was characterized. Tower formation was not observed in the commensal strain. The pCF10-containing bacteria formed a rigid base layer on day 1 and small aggregates on day 1. pCF10-containing biofilm forms heterologous towers on days two and three. Interestingly, mixed biofilms with both plasmid-containing and plasmid-free bacteria developed tower-like structures as early as day 1 and had larger resulting structures by day three. In the mixed population, we hypothesize that the induction of aggregation substance and cell clumping during plasmid transfer may further contribute to structure formation (5,10). Plasmid-free mCherry-labeled bacteria could be observed in the viscous biofilms between heterologous rigid structures; however, the rigid structures were predominantly composed of plasmid-containing cells. Occasionally, mCherry cells were observed in the rigid structures, we hypothesize that these cells represent transconjugants, where pCF10 was transferred by conjugation to mCherry-plasmid-free OG1RF. The formation of rigid structures can protect bacteria from antibiotics by reducing the penetration of the antibiotic but binding and sequestration of the antibiotic in the outer layers. Antibiotic resistance increased in the pCF10-containing biofilms as rigid structures were formed. We hypothesize that underflow, like that found in the gastrointestinal tract, the heterologous rigid structures may form protected microenvironments for sensitive regions of the biofilms. In future studies, fluorescently labeled antibiotics will be used to access the formation of protected microenvironments in biofilms underflow. Previous studies in the laboratory demonstrated that the presence of pCF10 protects E. faecalis from hydrogen peroxide oxidative stress. E. faecalis produces hydrogen peroxide. Higher levels of hydrogen peroxide can be detected in rigid structures. The presence of pCF10 is known to increase the size of heart vegetations during endocarditis and hydrogen peroxide is a known activator of platelet activation (12,19). In these studies, the presence of pCF10 increased platelet activation in pCF10 containing biofilms. Software toolboxes are currently being developed to quantitate visual observations. The role of hydrogen peroxide is supported in our preliminary experiment revealing catalase treatment reduced platelet activation. Studies are ongoing to mutate the aroc and menB gene of E. faecalis, which contribute to hydrogen peroxide production (35). We will compare platelet activation in knockout (double or single) E. faecalis and the wild-type strain. For future studies, several of the preliminary data need to be repeated to further the study. We will repeat quantitative hydrogen peroxide production in the catalase experiments. We will also finish knocking out the aroc and men B gene of E. faecalis responsible for hydrogen peroxide and then compare platelet activation to the control strain. / Microbiology and Immunology

No description available.