New bioprocess technologies underpinning future manufacture of magnetosome products

Li, Hong (2019). New bioprocess technologies underpinning future manufacture of magnetosome products. University of Birmingham. Ph.D.

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Abstract

Magnetic support based separations in biotechnological applications was initiated in the late 1970’s. Since then, magnetic supports have been widely applied in the laboratory and increasingly at process scales in hugely diverse applications. To date most of these have employed artificial chemically synthesized magnetic particles, but interest in naturally occurring magnetic materials made biologically is growing. Magnetosomes are one such example. These are needle-like chains of single-domain permanently magnetic membranewrapped crystals that act as a compass to allow magnetotactic bacteria navigate along geomagnetic field lines in search of optimal environmental oxygen levels. Their unique characteristics convey numerous advantages over chemically manufactured magnetic particles in biomedical and biotechnological settings, but future widespread application requires the development of commercial scale intensified high-yielding manufacturing platforms for magnetosome-based products.
Against the above the overall aim of this work has been to advance new bioprocess technologies underpinning future manufacture of magnetosome products. The starting point for this work was to develop a battery of flow cytometric tools for analysing the growth, viability, physiology of magnetotactic bacteria (Magnetospirillum gryphiswaldense MSR-1 was selected as a model organism) and their biomineralization of magnetic iron minerals. Specifically, methods for the determination of cellular concentration, cell size distribution, single-cell physiology and time dependent changes in intracellular PHA content and the chelatable iron pool were advanced.
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The next study was the development of a simple pH-stat fermentation strategy for production of M. gryphiswaldense MSR-1 and magnetosomes. Growth conditions were optimised with respect to biomass concentration, cellular magnetism (indicative of magnetosome production) and intracellular iron concentration using the previously developed flow cytometry analytics. High biomass and cellular iron contents of 4.2 g dry cell weight per litre and 33.1 milligrams per gram dry cell weight respectively were obtained.
The final piece of work describes the systematic advance of a fully scalable platform for extraction, recovery and purification of magnetosomes. The approach comprises single pass disruption of exponential phase Magnetospirillum gryphiswaldense MSR-1 cells in a commercial high pressure homogenizer, recovery and partial purification of magnetosomes by high gradient magnetic fishing in an automated ‘state-of-the-art’ magnetic separator, and final purification by magnetic micellar aqueous two phase separation. A magnetosome yield of nearly 45% was achieved, with 98.5% and >99% removal of polyhydroxyalkanoate and protein respectively

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):