No description available.

In a population of altruists, all individuals thrive. But altruists are exploited by cheating individuals which do not perform altruistic acts but still benefit from those. In these conditions cooperation cannot easily evolve. This issue is resolved by kin recognition: altruists recognise each other through the use of a conspicuous tag. These altruists do well until cheaters acquire the signalling tag and disrupt the cooperation. But altruists using a different tag can then invade the population, followed by new cheaters. This mechanism can lead to a diversity of tags coexisting in the population. However it has not yet been applied in realistic biological systems. In this thesis, I formulated mathematical and simulation models to investigate the effect of diversity on the evolutionary dynamics in systems where different altruists compete with cheaters. In particular, I focused on organisms producing public goods, i.e. goods that can profit to the whole population. I considered two biological systems models: gynodioecious populations of plants, where hermaphrodites produce pollen that can be used by female-only individuals, and bacteria producing an iron-chelating molecule, called siderophore, that can be exploited by both producers and non-producers. I found that diversity in gynodioecious plants is dependent on population structure. In particular, I found that the maximal level of diversity occurs when the population structure does not favour altruists or cheaters. Next, I found a number of important results in siderophore-producing bacteria. By considering a detailed ecological model, I derived Hamilton's rule in a metapopulation and found that the level of cooperation in a population depends on the length of interaction between strains. Finally, I discovered a novel evolutionary mechanism generating and maintaining diversity and showed that it results from non-equilibrium mechanisms. These findings explain why cheaters appear readily in experiments but are rare in natural populations. My results demonstrate the importance of integrating ecological details in order to understand the mechanisms leading to cooperation and diversity, and will provide a basis and framework for future studies on the emergence and maintenance of diversity.

Siderophores are low molecular weight organic compounds secreted into the environment by bacteria and fungi in response to iron stress. Significant levels of siderophores have been found in the rhizosphere of crop plants; however, their potential significance in terms of mobilizing iron and other micronutrient cations has been overlooked. This research project studied the occurrence of siderophores in some Saskatchewan soils, and their importance in complexing and increasing availability of Cu, Fe, Mn, and Zn. Twenty four soils were surveyed for siderophore levels using a bioassay which employed the siderophore-requiring bacterium, Arthrobacter jlavescens JG-9. Hydroxamate type siderophores (HS) in the range of 2.1 to 27.3 x 10-9 M deferrioxamine methane sulfonate (DFOM) equivalents were detected in these soils. There was no simple correlation between HS levels and soil pH, % organic carbon, % clay, or DTPA-extractable Cu, Fe, Mn, and Zn. A total of 210 bacteria were isolated from the rhizosphere of wheat roots grown in three soils (Medstead, Smeaton, and Choiceland), which contained the highest HS levels. Bacteria were screened for siderophore production using the Arthobacterjlavescens JG-9 bioassay and the Chrome Azurol-S chemical method. Out of the 210 isolates, 29 were found to be producing siderophore. The 29 siderophore-producing bacteria and 9 plant growth-promoting rhizobacteria (PGPR) were further screened for the most efficient siderophore-producing bacteria. Three bacterial strains, CH 16, R III and KC 21, were selected and identified as Pseudomonas fluorescens. The efficient strains were grown in broth culture and their siderophores extracted and purified by Bio-Gel P2 filtration. The purified siderophores were used to study the mechanisms by which siderophores could increase availability of micronutrient cations. It was shown that siderophores produced by these bacterial strains were able to complex not only with Fe, but also with Cu. Another way by which these siderophores increased the availability of micronutrient cations was through dissolution of iron-hydroxide, thereby releasing specifically adsorbed and coprecipitated Cu, Mn, and Zn. The qualitative characterization of bacterial siderophores indicated that some components of these compounds are heat labile, and have maximum absorbance between 375 to 425 nm. The scanning of these siderophores in the infrared region indicated the presence of carboxyl and amino groups. My research shows that Saskatchewan soils contain siderophore levels that are high enough to increase the availability of Cu, Fe, Mn, and Zn. However, the ability of siderophore-producing bacteria to colonize plant roots under field conditions may be limited. Therefore, the use of siderophore-producing bacteria as seed inoculants might increase the level of siderophores in the rhizosphere and facilitate micronutrient nutrition of crops.

Siderophores are a series of important iron chelators secreted by many bacteria that normally have high affinity of iron ions and contain hydroxamate, catecholate and carboxylate and other ligand groups. These organic ligands play significant roles in bacterial metabolism: solubilising iron (III) from environments, enabling iron uptake and acting as a cell-signalling molecule to control gene expression. Recent observations of initial stages of Pseudomonas aeriginosa biofilm formation on metal oxides surfaces indicate that siderophores may also facilitate bacterial adhesion to metals. However, details of how siderophores interact with metal surfaces and the relationship of their chemical nature with bacterial adhesion were not fully understood. To test the generality of bacteria attachment to metals via siderophores, the adsorption behaviour of siderophores and their functional ligands groups on particle films of metal oxides were investigated with in-situ ATR-IR spectroscopy. In this study, nanoparticle films of titanium oxide, boehmite, iron oxide and chromium oxyhydroxide were prepared as substrates to simulate titanium, alumnium, stainless steel surface and more detailed work were carried out on titanium dioxide. Monohydroxamic acids (acetohydroxamic acid, N-methylformohydroxamic acid, N-methyl-acetohydroxamic acid and 1-hydroxy, 2-piperidone) and catechol and catechol-like (L-dopa and esculetin) ligands were selected as modelling compounds for the most frequently occured functional groups in natural siderophores. IR spectra of these ligands in aqueous solution and adsorbed on TiO₂ were obtained with a flowing cell system fit to a horizontal accessory by in situ ATR-IR spectroscopy and interpreted based on vibrational mode analysis with density function theory. Results show that all these ligands can form surface complexes with metal surfaces and possible adsorption modes of these molecules were discussed. The pH dependence of absorbance of IR absorption of these adsorbed ligands showed that most of the ligands exhibited maximium adsorption to TiO₂ at about pH 8, only N-methylformohydroxamic acid, 1-hydroxy, 2-piperidone groups having maximum absorption at pH~3 and pH~6. Infrared spectroscopic studies of adsorbed siderophores (desferroximme B, enterobactin and pyoverdine) were also carried out in variation of concentration and pH. Possible adsorption modes of these iron scavenger ligands on TiO₂ and other metal oxides were discussed. Results showed that all these ligands adsorbed on metal oxide surfaces and form surface complex via hydroxamate or catecholate lignd groups which confirm the generality of siderphore-metal bond formation. Siderophore based-bacterial adhesion to metals of was conducted with Pesudomonas aeruginosa and E. coli strains on titanium oxide and iron oxide films. These observations support that siderophore play a significant role in bacterial adhesion to metals. Further work needs to be carried out on the wider involvement of siderophores in bacterial adhesion initiation to metals and siderophore-mediated iron transport.

Professional paper (MS)--Montana State University--Bozeman, 2009. / Typescript. Chairperson, Graduate Committee: Abigail Richards. Includes bibliographical references (leaves 53-58).

Thesis (Ph. D.)--University of Idaho, 2005. / Also available online in PDF format. Abstract. "December 2005." Includes bibliographical references.

The Rhizobia comprise one of the most important groups of beneficial bacteria, which form nodules on the roots (rarely on the stems) of leguminous plants. They live within the nodules and reduce atmospheric nitrogen to ammonia, which is further assimilated by plants into required nitrogenous compounds. The Rhizobia in return obtain nutrition from the plant. Rhizobia are free-living soil bacteria and have to compete with other microorganisms for the limited available iron in the rhizosphere. In order to acquire iron Rhizobia have been shown to express siderophore-mediated iron transport systems. Rhizobium leguminosarum IARI 917 was investigated for its ability to produce siderophore. It was found to produce a dihydroxamate type siderophore under iron restricted conditions. The siderophore was purified and chemically characterized. The ESMS, MS/MS and NMR analysis indicate the dihydroxamate siderophore to be 'schizokinen', a siderophore reported to be produced by Bacillus megaterium that shares a similar structure to 'rhizobactin 1021' produced by Sinorhizobium meliloti 1021. This is the first report of production of schizokinen by a strain of R. leguminosarum, therefore it was carefully investigated to confirm that it is indeed 'schizokinen' and not a degradation product of 'rhizobactin 1021'. Since ferric-siderophore complexes are transported across the outer membrane (OM) into the periplasm via an OM receptor protein, R. leguminosarum IARI 917 was investigated for the presence of an OM receptor for 'ferric-schizokinen'. SDS PAGE analysis of whole cell pellet and extracted OM fractions indicate the presence of a possible iron-repressible OM receptor protein with the molecular weight (MW) of approximately 74 kDa.

No description available.

The water solubility of transition metals constrain their use in the bioinorganic chemistry of organisms. Iron(III) is one of the most sought-after metals by organisms; however, it has poor solubility in water at physiological pH. Prior to the great oxidation event (GOE) 2.4 billion years ago, iron was more bioavailable in the 2+ oxidation state. This higher water solubility sustained a greater supply of iron to organisms that required it. Since the GOE and the oxidation of Fe(II) to Fe(III), organisms have been evolving methods to sequester iron from the environment. One method to obtain iron is through the use of low molecular weight molecules called siderophores which solubilize Fe(III) from their environment through chelation. The strongest siderophore to date is enterobactin (ent) which forms a Fe-ent complex with an association constant of 1049. While iron is utilized by most organisms, titanium is also a bioactive metal. Titanium is second to iron in abundance of transition metals in the Earth’s crust and is becoming increasingly relevant in medicine, technology, and commercial goods. Titanium(IV) (the most common oxidation state of titanium) also has a larger charge to size ratio than Fe(III) and may outcompete iron for binding. The already high abundance and increasing usage of titanium in the developed world leads to possible undocumented interactions between titanium and siderophores. In an attempt to address the natural selection of the chemical elements during bioinorganic evolution, the solution interactions of Ti(III), Ti(IV), Fe(II), and Zn(II) with sulfide in a solution mimicking the sulfidic early ocean were explored. Anaerobic metal solutions were added to solutions with ocean-mimicking salts, acetic acid buffer, and increasing concentrations of sodium sulfide. After equilibration, the soluble metal ion concentrations were measured using ICP-OES. Catechol ligands are important bioinorganic chelators. The synthesis and crystallization of the disodium, dilithium, and diammonium salts of the model catechol ligand 4,5-dihydroxy-1,3-benzenedisulfonate (tiron) are described. The dilithium and diammonium salts were synthesized from the disodium tiron salt by cation metathesis. The crystals were obtained by solvent evaporation in either alcohols or water. Crystal structures were acquired, solved, and analyzed revealing inter- and intramolecular interactions in the dication tiron crystal structures. The synthesis of the siderophore enterobactin (ent) was improved upon from published methods to increase purity. Following the synthesis of ent, spectrophotometric techniques were used to analyze Ti-ent complex stability. Spectrophotometric titrations were carried out from p[H] 2-12 revealed that the fully catecholate bound [Ti(ent)]2- complex was the only species in the p[H] range 2-9. Above a p[H] value of 9 the trilactone backbone apparently hydrolyzed. This result indicates that protons cannot outcompete Ti(IV) binding at low p[H] and hydroxide cannot outcompete ent for binding to Ti(IV) at high p[H]. Using various Ti(IV)-ligand complexes, the log b110 for Ti-ent was probed at pH 6. The complex [Ti(DFOB)]+ (log b110 = 38.1) with 1,000 fold excess desferrioxamine B (DFOB) was unable to compete with ent and every addition of ent lead to the formation of [Ti(ent)]2- yielding a lower limit log b110 of 52.9. The catecholate ligand tiron was used in a 4,000:1 ratio of tiron:Ti(IV) forming [Ti(tiron)3]8- (log b130 = 57.6) to attempt to compete with ent. This yielded a lower limit log b110 for [Ti(ent)]2- of 61.2. Kinetic studies of titanium sequestration from titanium containing species was also investigated. Using Ti(IV) complexes such as [Ti(DFOB)]+, [Ti(citrate)3]8-, and the titanium complex of human serum transferrin (Ti2HsTf) as the Ti(IV) source, the rate of titanium sequestration by ent was probed. Taken together, these findings indicate that ent is a strong binder of Ti(IV); however, it binds relatively slowly. Strong binding ligands are able to coordinate and dissolve metal ions from the surface of metal oxides. Titanium mostly exists in the solid oxide form in the Earth’s crust, thus solubilization of these oxides may be important for Ti(IV) incorporation into an organism. To determine the effects of ent in solution at a TiO2 interface, 50 mM ent was added to a series of suspensions of TiO2 at pH 5 ± 0.5 with different loadings for 176 h. The [Ti]max for all anatase trials averaged to be approximately 20 – 25 mM indicating 40 – 50% ent efficacy for TiO2 dissolution. This value was compared to previously reported TiO2 dissolution by 2 mM DFOB at pH 2 as well as dissolution of 50 mM and 150 mM DFOB and tiron, respectively, at pH 5 ± 0.5. Surface interactions between ent and anatase were probed using ATR-IR. One extension of this work related to the avid Fe(III) ligand deferasirox (DSX). DSX is an orally administered chelator for Fe(III) overload. A Ti(IV)-DSX complex may be useful as an anticancer drug. The solution chemistry of DSX with Ti(IV) was characterized utilizing spectrophotometric and mass spectrometric techniques. A series of titrations with Ti(IV) and DSX from pH 6.7-11.2 revealed two distinct species. Additions of [Ti(HDSX)(DSX)]- to bovine serum albumin (BSA) indicated that the [Ti(HDSX)(DSX)]- complex binds to BSA. This transfer is possibly an important step in the efficacy of Ti(IV) anticancer drugs and may relate to the possible mechanism for Ti(IV) delivery into cancerous cells. / Chemistry

Thesis (Ph. D.)--University of Missouri--Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves: 157-166). Also available on the Internet.