Microbial and enzymatic conversion of levulinic acid, an alternative building block to fermentable sugars from cellulosi
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MINI-REVIEW
Microbial and enzymatic conversion of levulinic acid, an alternative building block to fermentable sugars from cellulosic biomass Hiroshi Habe 1
&
Yuya Sato 1 & Kohtaro Kirimura 2
Received: 29 May 2020 / Revised: 25 July 2020 / Accepted: 2 August 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Levulinic acid (LA) is an important chemical building block listed among the top 12 value-added chemicals by the United States Department of Energy, and can be obtained through the hydrolysis of lignocellulosic biomass. Using the same approach as in the catalytic production of LA from biomass, catalytic methods to upgrade LA to higher value chemicals have been investigated. Since the discovery of the catabolic genes and enzymes in the LA metabolic pathway, bioconversion of LA into useful chemicals has attracted attention, and can potentially broaden the range of biochemical products derived from cellulosic biomass. With a brief introduction to the LA catabolic pathway in Pseudomonas spp., this review summarizes the current studies on the microbial conversion of LA into bioproducts, including the recent developments to achieve higher yields through genetic engineering of Escherichia coli cells. Three different types of reactions during the enzymatic conversion of LA are also discussed. Key points • Levulinic acid is an alternative building block to sugars from cellulosic biomass. • Introduction of levulinic acid bioconversion with natural and engineered microbes. • Initial enzymatic conversion of levulinic acid proceeds via three different pathways. • 4-Hydroxyvalerate is one of the target chemicals for levulinic acid bioconversion. Keywords Biorefinery . Cellulosic biomass utilization . Enzymatic conversion . Levulinic acid . Microbial conversion
Introduction The conversion of cellulosic materials into fermentable sugars is pivotal for the synthesis of useful chemicals and energy because cellulose is the most abundant organic compound on Earth (Klemm et al. 2005). However, cellulose in plants occurs as highly crystalline microfibrils embedded in a matrix of hemicellulose, pectin, and lignin that imparts structural strength in plants and makes it resistant to be attacked by hydrolytic enzymes (Hasunuma et al. 2013). Recently, the catalytic conversion of lignocellulose into alternative building * Hiroshi Habe [email protected] 1
Environmental Management Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 16-1 Onogawa, Tsukuba, Ibaraki 305-8569, Japan
2
Department of Applied Chemistry, Faculty of Science and Engineering, Waseda University, Tokyo 169-8555, Japan
block chemicals other than fermentable sugars has attracted much attention. One such building block chemical is levulinic acid (LA) (Pileidis and Titirici 2016; Werpy and Petersen 2004). LA has been produced from cellulose or sugars in the presence of large quantities of homogeneous inorganic acids such as H2SO4 and HCl (Girisuta et al. 2008; Hayes et al. 2006; Signoretto et al
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