Cellulosic hydrocarbons production by engineering dual synthesis pathways in Corynebacterium glutamicum

Abstract

Background Lignocellulose provides the only practical carbohydrates feedstock for sustainable bioproduction of hydrocarbons as future alternative of fossil fuels. Production of hydrocarbons from lignocellulose is achieved by a biorefinery process chain including pretreatment to breakdown the crystalline structure for cellulase-catalyzed hydrolysis, detoxification of inhibitory compounds generated during pretreatment, enzymatic hydrolysis to fermentable monosaccharide sugars, and fermentation to hydrocarbon products. The major barriers on fermentative production of hydrocarbons from lignocellulose include two aspects: one is the inherent stress of pretreatment-derived inhibitors on microbial cells, the other is the toxicity of hydrocarbons to cell membranes. The microbial cell factory should be tolerant to both inhibitor stress and hydrocarbons toxicity. Results Corynebacterium glutamicum was selected as the starting strain of hydrocarbons synthesis since it is well adapted to lignocellulose hydrolysate environment. The dual hydrocarbon synthesis pathways were constructed in an industrial C. glutamicum S9114 strain. The first pathway was the regular one in microalgae composed of fatty acyl-acyl carrier protein (fatty acyl-ACP) reductase (AAR) and aldehyde deformylating oxygenase (ADO) with fatty acyl-ACP as precursor. The second pathway was the direct decarboxylation of free fatty acid by fatty acid decarboxylase (OleT) using the rich fatty acids from the disruption of the transcriptional regulator fasR gene. The transmembrane transportation of hydrocarbon products was avoided by secretively expressing the fatty acid decarboxylase (OleT) to the extracellular space. The hydrocarbons generation from glucose reached 29.2 mg/L, in which the direct decarboxylation pathway contributed more than 70% of the total hydrocarbons generation, and the AAR–ADO pathway contributed the rest 30%. Conclusion The dual hydrocarbon synthesis pathways (OleT and AAR–ADO pathways) were constructed in the inhibitors tolerant C. glutamicum S9114 strain for hydrocarbon production using lignocellulose feedstock as the starting feedstock. When corn stover was used for hydrocarbons production after dry acid pretreatment and biodetoxification, the hydrocarbons generation reached 16.0 mg/L. This study provided a new strategy for hydrocarbons synthesis using microbial cell factory suitable for lignocellulose feedstock.

Production Optimization and Biochemical Characterization of Cellulase from Geobacillus sp. KP43 Isolated from Hot Spring Water of Nepal

“…Furthermore, metabolic engineering of cellulolytic microbes to enhance the bioethanol production can be another strategy to improve the utility of potent microbial strains with industrial applications [ 68 – 70 ]. This approach was also adopted more recently in Corynebacterium glutamicum for hydrocarbon biofuel production from lignocellulosic biomass [ 71 ].…”

Changes in pH Values Allow for a Visible Detection of the End Point in Submerged Liquid Biodetoxification during Biorefinery Processing

“…The acid components during the submerged liquid biodetoxification were determined by GC-MS. 30 The nonderivatization method was used to avoid the interference of the derived fatty acid for measurement of the original free acid in culture broth. The supernatant of hydrolysate was mixed with 50% (w/w) sulfuric acid and anhydrous ether in a ratio of 10:1:4.…”