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About MacSphere

MacSphere is McMaster University's Institutional Repository. MacSphere brings together the institution's scholarly works under one umbrella to preserve and provide ongoing open access to them. MacSphere works have been selected and deposited by members of the McMaster community as part of our collective committment to sharing our knowledge with the world.

MacSphere is supported and hosted by the McMaster University Libraries.

To contribute, sign on to MacSphere with your McMaster Account. If you have any questions, refer to the user guide or contact the MacSphere Support Team for assistance.

Students wishing to deposit their PhD or Masters thesis, please follow the instructions outlined by the School of Graduate Studies.

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Recent Submissions

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    Defining a minimal symbiotic genome of the legume symbiont Sinorhizobium meliloti
    (2026) Kearsley, Jason Vincent Shields; Finan, Turlough; Biology
    Identifying and understanding bacterial genes involved in the formation of N2-fixing root nodules is of agricultural and environmental interest. Sinorhizobium meliloti is a model bacterium for studying the rhizobia-legume symbiosis. Most genes with direct functions in symbiotic nitrogen fixation (SNF) are harboured on two megaplasmids: pSymA (1354 kb) and pSymB (1683 kb). This thesis describes work on minimizing the pSymB replicon to establish a gene complement sufficient for a robust SNF phenotype. It also outlines my contribution towards establishing that 58 genes (63 kb) from pSymA are sufficient for a robust SNF phenotype. Megaplasmid pSymB is evolutionarily older and more chromosomal-like (i.e. a chromid) than the more recently acquired pSymA replicon. Both large-scale deletion analyses (top-down) and assembly-based methods (bottom-up) to minimize pSymB were conducted. These analyses revealed that minimizing pSymB results in a large symbiotic penalty. An initial minimization of pSymB to 261 kb (15%) resulted in SNF with a large degree of plant genotype-dependent variation. This served as a platform to demonstrate that additional regions housing undiscovered auxiliary genes are necessary for the efficient SNF. Accordingly, a minimized 673 kb replicating pSymB that facilitated consistent SNF was isolated. A cumulative deletion strategy refined this set to 276 kb (16% of pSymB) without further SNF impairment. In addition to the deletion approach, we developed a methodology that targeted the assembly of pSymB loci into discrete clusters followed by their iterative integration into a S. meliloti strain lacking pSymB. A set of 101 genes (114 kb) from pSymB proved capable of routinely forming nodules with SNF at 25% wild-type levels. By combining the minimized pSymA and iv pSymB sets, the smallest genome capable of forming root-nodule symbioses was established. This should serve as a powerful chassis for gain-of-function approaches to studying SNF.
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    Approved Minutes: February 2026 Graduate Council
    (2026) School of Graduate Studies
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    Clinical Pharmacology, Therapeutics and Toxicology High Priority Topics Across Core Clerkship Rotations
    (2025-09-02) Gandhi, Bhavya; Khakban, Iliya; Bracken, Keyna; Levinson, Anthony J; Levine, Mitchell; Holbrook, Anne M; Medicine
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    Clinical Pharmacology, Therapeutics and Toxicology Objective and Resource Mapping Across Pre-Clerkship
    (2025-02-01) Gandhi, Bhavya; Khakban, Iliya; Bracken, Keyna; Levinson, Anthony J; Levine, Mitchell; Holbrook, Anne M; Medicine