Modular Engineering of Biomass Degradation Pathways

Abstract

Production of fuels and chemicals from renewable lignocellulosic feedstocks is a promising alternative to petroleum-derived compounds. Due to the complexity of lignocellulosic feedstocks, microbial conversion of all potential substrates will require substantial metabolic engineering. Non-model microbes offer desirable physiological traits, but also increase the difficulty of heterologous pathway engineering and optimization. The development of modular design principles that allow metabolic pathways to be used in a variety of novel microbes with minimal strain-specific optimization will enable the rapid construction of microbes for commercial production of biofuels and bioproducts. In this review, we discuss variability of lignocellulosic feedstocks, pathways for catabolism of lignocellulose-derived compounds, challenges to heterologous engineering of catabolic pathways, and opportunities to apply modular pathway design. Implementation of these approaches will simplify the process of modifying non-model microbes to convert diverse lignocellulosic feedstocks.

Engineered Pseudomonas putida KT2440 co-utilizes galactose and glucose

“…However, we did observe that glucose was utilized more rapidly than galactose in QP607. Fortunately, because galactose is a less abundant sugar than glucose in lignocellulose (approximately 1:30 ratio in corn stover hydrolysate [2]), the current slower utilization rate of galactose should still be sufficient for most real-world settings. Based on the similarity to the ED pathway and the lack of detected products, the galactose was presumably completely oxidized to CO 2 via the TCA cycle in these strains.

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“…Biological valorization of sugars and lignin from plant-based biomass to commodity chemicals is a potential route to renewable and sustainable alternatives. Although different feedstocks and pretreatment processes yield different available substrates for microbial conversion, several sugars are regularly detected in hydrolysate streams [1, 2]. While glucose is typically the most abundant, xylose, galactose, mannose, and arabinose are all present as well at different concentrations.…”

“…There are two common pathways for galactose catabolism in bacteria: the Leloir (LL) pathway and the De Ley–Doudoroff (DLD) pathway [2]. In the LL pathway, galactose is phosphorylated and then converted to glucose-1-phosphate through a cyclic pair of transferase/epimerase reactions with uridyl monophosphate intermediates [22, 23].…”

Structure and Chemical Reaction Mechanism of LigU, an Enzyme That Catalyzes an Allylic Isomerization in the Bacterial Degradation of Lignin

“…The reaction was monitored by 1 H NMR spectroscopy using the water suppression pulse program Watergate zggpw5 pulse sequence. 18 The deuterated L-malate, made from the combined activities of LigI, LigU, LigJ, LigK, and malate dehydrogenase, was compared to the deuterated L-malate formed from the action of fumarase with fumarate in D 2 O and also with [2, The hydrogen−deuterium exchange reactions were initiated by adding 580 μL of D 2 O containing 200 mM KH 2 PO 4 /KOD (pD 6.6−7.0) to a lyophilized sample of KCH. A total of 1.0 nM LigU and 66 nM bovine serum albumin (BSA) was added to the reaction mixture, and the reaction followed by 1 H NMR spectroscopy.…”

“…However, it is an underutilized renewable resource due to its recalcitrant nature as a complex heteropolymer. Lignin is comprised of phenylpropanoid units (guaiacyl, syringyl, and p -hydroxyphenyl precursors) that couple to one another through C–C and C–O bonds. , The natural recycling of lignin occurs through the combined actions of eukarya, archaea, and bacteria . In general, fungi are responsible for the depolymerization of lignin, and bacteria further metabolize the monomeric units into viable carbon sources.…”