Deletion of L-lactate dehydrogenase from Lactiplantibacillus plantarum NC8 and lactic acid fermentation optimization of resulting mutant strain NCD8 for production of optically pure lactic acid from municipal solid waste derived sugars

Abstract

Polylactic acid is a biodegradable plastic which is typically bio-based, and this growing market for polylactic acid is set to drive the growth of the market for its monomer, lactic acid. Lactic acid may be produced from first generation crops like industrial maize, sugar cane, or sugar beet. However, exploration of second-generation waste derived lignocellulosic biotechnological feedstocks like the organic fraction of municipal solid waste (OFMSW) could contribute to a circular economy. The company partner, Fiberight Ltd, has developed a process to separate comingled municipal solid waste (MSW) into several high value material fractions using their patented HYDRACYLCE™ process. One of the outputs of this process is a lignocellulosic fibre containing much of the paper and cardboard from the original comingled municipal solid waste. This lignocellulosic fibre fraction may then be converted to platform sugars using enzymatic hydrolysis technologies. This project focused on technologies for the conversion of these platform sugars into renewable, biobased, lactic acid. Lactic acid bacteria, like current and former members of the genus Lactobacillus, are able to convert almost all of the sugar they consume into lactic acid. However, the lactic acid they produce may be either of the lactic acid enantiomers (D- or L-) or a mixture of both. If lactic acid is to be used to produce polylactic acid, it must be enantiomerically pure. This project focused on improving the enantiomeric purity of lactic acid produced by a strain of Lactiplantibacillus plantarum (formerly Lactobacillus plantarum) and investigating the optimisation of fermentation conditions to allow the modified strain to efficiently convert the platform sugars produced by Fiberight Ltd. into lactic acid. Fermentation temperature, pH, and amount of complex nutrients added to fermentations were investigated, and the challenges of transitioning from a simple shake flask fermentation system to miniature bioreactors were explored.

Date of Award	2023
Original language	English
Awarding Institution	Aberystwyth University
Supervisor	David Bryant (Supervisor) & Joe Gallagher (Supervisor)