Thèse de doctorat : Sciences du vivant, géosciences et sciences de l'environnement. Biogéochimie et écosystèmes : Bordeaux 1 : 2008. Thèse de doctorat : Sciences du vivant, géosciences et sciences de l'environnement. Biogéochimie et écosystèmes : Université Hassan II, Casablanca, Maroc : 2008. / Titre provenant de l'écran-titre.

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Ecology and Evolution." Includes bibliographical references (p. 148-163).

Parasite population dynamics and the evolution of life history characteristics are strongly correlated with the processes of host infection, survival within a host and reproduction, with each process posing a challenge to the parasitic lifestyle. Macroparasites living in marine environments have evolved extreme changes in physiology, morphology and life history traits to overcome these challenges. This study focused on the infective and reproductive stage of the parasitic isopod, Cymothoa excisa, a common parasite on Atlantic croaker, (Micropogonias undulatus), along the Texas coast. A two year survey identified infection rates and the relationship between fish density and size and parasite load, size and fecundity. Isopod morphology was quantified for each life stage, identifying shape transitions through ontogeny and sex change. Sex change in C. excisa was found to be driven by the absence of conspecific parasites within a host, where sex change only occurred in the first individual to arrive. To understand the infective stage of C. excisa parasite energetics and host detection mechanisms were tested. Parasites with free-living life stages have a narrow window to infect a host and have evolved a number of mechanisms to detect and locate a host. I used a series of energetic experiments to determine an infection window for free-swimming larvae (mancae) and behavioral response experiments testing both visual and chemical cues associated with host detection. Mancae were found to have a narrow infection window, where mancae began searching for a host as soon as they are born, but quickly switch to an ambush strategy to conserve energy. Mancae were also found to be responsive to both visual and chemical cues from its common fish host, as well as a non-host fish, indicating that chemical cues are used in host detection, but chemical specificity is not a mechanism that C. excisa uses to find its common host. The results from this study have implications to parasitic species and their hosts, as well as to other areas of study, including population and ecosystem dynamics. / text

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Molecular and in vitro comparisons were performed using two isolates of Encephalitozoon hellem, one from an avian host and one from a human host, and one isolate of Encephalitozoon cuniculi from a rabbit. The molecular comparisons were performed by amplifying and sequencing the gene coding for a zinc metallo-aminopeptidase from cDNA and gDNA obtained from each of the isolates. The E. hellem sequences shared >99 % identity between each other and 70% identity with the E. cuniculi sequences. Conserved HEXXH and GXMEN motifs located within the sequences classify the protein as an aminopeptidase of the M1 family, with at least one zinc atom required for catalytic activity. In vitro growth comparisons of the isolates described above were performed under simulated "mammalian and avian conditions". The models utilized mammalian and avian cell lines and sera at incubation temperatures of 37 °C and 40 °C, respectively. Three separate experiments were performed. E. cuniculi grew best under the mammalian model and significantly better than both E. hellem isolates under this model. The E. hellem isolates were able to infect and replicate under both the mammalian and avian models, which reflects the zoonotic potential of these isolates.

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Since host cell-derived thymidine is not incorporated into Chlamydia trachomatis DNA, we hypothesized that chlamydiae must synthesize dTMF de novo for DNA replication. The only known enzyme performing de novo dTMP synthesis is thymidylate synthase (TS). The goals of this thesis were to provide biochemical evidence for the existence of TS in chlamydiae, to investigate the mechanism by which the parasite obtains folate, a necessary cofactor for TS, and to provisionally characterize chlamydial TS. Results of a series of in situ experiments using a mutant cell line as chlamydial host which is incapable of de novo dTMP synthesis suggest that C. trachomatis converts dUMP into dTXP. In vitro experiments conclusively establish these findings by the demonstration of TS activity in extracts prepared from host-free chlamydial reticulate bodies. Furthermore it was found that both sulfa-sensitive and sulfa-resistant chlamydial strains can synthesize folates de novo; however strains vary significantly in their ability to transport preformed folates from the host cell. A C. trachomatis gene which is capable of complementing thymidine auxotrophy in Escherichia coli deficient in TS was cloned. Auxotrophic E. coli containing the complementing chlamydial DNA sequence converts dUMP to dTMP, using methylene tetrahydrofolate as the cofactor. The complementing DNA fragment contains an open reading frame of 1587 bp. Surprisingly this open reading frame shows absence of sequence homology to known TS. Unique in vitro characteristics shared by the enzyme activities from both chlamydial extract and recombinant E. coli extract suggest that C. trachomatis might encode a novel TS.

Research on the interactions between microbes and polymeric materials constitutes an important part in antimicrobial identification and provides an insight into microbial response on the polymer surfaces. Herein, a high-content screening method with polymer microarray technology was developed to investigate microbe-polymer interactions, especially in studying adhesion/repellence of microbes (bacteria and parasites). Firstly, the polymer microarray approach was used to successfully identify polymers which either selectively captured or prevented the binding of major food-borne pathogen, Salmonella Typhimurium. A parallel study with a lab strain of Escherichia coli was also carried out, revealing polymers which either displayed a common binding activity or which exhibited species discrimination. Likewise, this polymer microarray technology was applied to more bacterial strains, such as Campylobacter, Clostridium, Streptococcus, Klebsiella and their cocktails to discover families of substrates that displayed strong broad-spectrum bacterial non-binding activity. These synthetic polymers represented a novel class of coating materials which can be used to prevent surface colonisation and subsequent formation of bacterial biofilms. The study of protozoan-polymer interactions was also explored in this thesis. Polymers were identified which either bound or prevented parasites (Crysporidium parvum and Giardia lamblia) binding. Material properties, including wettability, surface roughness and polymer composition were analysed to study correlation of parasite binding and the generation of polymer structure function relationships.