Suzuki, Motoshi (1988) Development of a process for the production of propylene oxide in methane-oxidising bacteria. PhD thesis, University of Warwick.

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Abstract

The aim of this project is to develop a process for the production of propylene oxide (PO), using methane-oxidising bacteria. At the beginning, a difficult problem needed to be solved for the development of this process i.e. the short life-span of the biocatalyst.

Experiments showed that the cells of the methane-oxidising bacterium, Methylococcus capaulatus (Bath) lost their catalytic activity within 30 minutes under the conditions of high PO production. The inactivation of the biocatalyst was largely Independent of externally-accumulated PO but was totally dependent on PO produced in vivo under conditions of high PO production. The cells lost their activity without any external accumulation of PO under those conditions where PO was produced. Prior to the research of the present writer, it had been concluded that external PO inactivated the biocatalyst. A specific PO productivity of more than 700 naol PO produced/min/mg cells was obtained in the work reported here. However, by increasing the PO productivity more than 200 aU/mg cells, the cells lost their activity rapidly and their half-life lasted 7 minutes.

In order to overcome the short life-span of the biocatalyst, a reactivation of the inactivated cells had to be devised. The methane-oxidising bacteria contain an enzyme, methane monooxygenase (MM0) which oxidises methane to methanol and also oxidises propylene to P0. The UNO was irreversibly inactivated by acetylene or by P0, however this inactivated MM0 was reactivated by subjecting the cells to reactivation treatment. This reactivation process is a phenomenon not previously known about. In order to reactivate the inactivated MMo, the cells required carbon, nitrogen and sulphur sources. In addition, a suitable oxygen and temperature regime was required for the reactivation process. The requirement of nutrients for reactivation and the inhibition of reactivation by the addition of chloramphenicol led to the conclusion that protein synthesis was associated with the reactivation process. Furthermore, it was found that MMo synthesis was completely inhibited by a detectable amount of methanol in the cell suspensions. Copper was not required for the reactivation of cells which contained particulate MM0.

Two types of inactivation mechanism were assumed under the conditions of P0 production. These are the inactivation of MMo and the inactivation of the biocatalyst by a means not yet identified. When the MMo only was inactivated, it was reactivated quickly. However when these cells were inactivated under conditions of high P0 production, they required three times as long a period for complete reactivation than did those cells which had been inactivated by acetylene. This delay in the reactivation process was thought to be due to a concealed inactivation (unidentified inactivation) factor. The latter was thought to be caused by the accumulation of P0 within the cells. The intracellular P0 concentration was calculated on the basis of the retention time of P0 in the cells, and its concentration appeared to be related to P0 productivity. The concealed inactivation was assumed to be due to a solvent-like effect of P0 in the cells and not from an alkylation effect.

In order to develop a P0 production process using the reactivation system, Mathylocystim paryus (0BBP) was selected as the best organism from 25 methanotrophs. The reactivation system, the growing-call process (single stage) and the two-stage reactivation process were designed and operated. Using the growing-cell process, continuous P0 production was achieved at a rate of 12 g/l/day for a period of more than three weeks.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QD Chemistry Q Science > QR Microbiology
Library of Congress Subject Headings (LCSH):	Propylene oxide, Methanotrophs
Official Date:	December 1988
Dates:	Date Event December 1988 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	Department of Biological Sciences
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Dalton, Howard
Sponsors:	International Institute of Entomology
Format of File:	pdf
Extent:	([28], 330 leaves : illustrations
Language:	eng

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