An Integrated Process for <scp>l</scp>-Tyrosine Production from Sugarcane Bagasse

Abstract

Microbial fermentation of lignocellulosic materials is a promising avenue for sustainable production of amino acids. Conventional microbes used in amino acid production consume sugars derived from hydrolysis of cellulose and hemicellulose and leave the lignin component unutilized. However, lignin contains up to 12% p-coumaric acid (pCA) by weight, which can be recovered during alkaline pretreatment and potentially used to produce the amino acid l-tyrosine. In this study, we explored this route of l-tyrosine production from pCA and used it in parallel with conventional microbial fermentation to form an integrated process for producing l-tyrosine from sugarcane bagasse biomass. From 1 g of sugarcane bagasse, an optimized alkaline hydrolysis step was performed that efficiently delignified the biomass and recovered 44 mg of pCA. The pCA obtained was converted into l-tyrosine with 49% molar conversion yield through biotransformation with whole Escherichia coli cells expressing a tyrosine ammonia lyase (TAL), yielding 24 mg of l-tyrosine. The alkaline-treated biomass residue was efficiently digested by exogenously added hydrolytic enzymes and utilized by a l-tyrosine-producing Escherichia coli strain, yielding another 25 mg of l-tyrosine. The l-tyrosine yield from the pCA biotransformation route was almost equal to that from the fermentation route, highlighting the significance of this newly described biotransformation process.