Abstract
BackgroundLignocellulosic biomass is an attractive and sustainable alternative to petroleum-based feedstock for the production of a range of biochemicals, and pretreatment is generally regarded as indispensable for its biorefinery. However, various inhibitors that severely hinder the growth and fermentation of microorganisms are inevitably produced during the pretreatment of lignocellulose. Presently, there are few reports on a single microorganism that can detoxify or tolerate toxic mixtures of pretreated lignocellulose hydrolysate while effectively transforming sugar components into valuable compounds. Alternatively, microbial coculture provides a simpler and more efficacious way to realize this goal by distributing metabolic functions among different specialized strains.ResultsIn this study, a novel synthetic microbial consortium, which is composed of a responsible for detoxification bacterium engineered Pseudomonas putida KT2440 and a lactic acid production specialist Bacillus coagulans NL01, was developed to directly produce lactic acid from highly toxic lignocellulosic hydrolysate. The engineered P. putida with deletion of the sugar metabolism pathway was unable to consume the major fermentable sugars of lignocellulosic hydrolysate but exhibited great tolerance to 10 g/L sodium acetate, 5 g/L levulinic acid, 10 mM furfural and HMF as well as 2 g/L monophenol compound. In addition, the engineered strain rapidly removed diverse inhibitors of real hydrolysate. The degradation rate of organic acids (acetate, levulinic acid) and the conversion rate of furan aldehyde were both 100%, and the removal rate of most monoaromatic compounds remained at approximately 90%. With detoxification using engineered P. putida for 24 h, the 30% (v/v) hydrolysate was fermented to 35.8 g/L lactic acid by B. coagulans with a lactic acid yield of 0.8 g/g total sugars. Compared with that of the single culture of B. coagulans without lactic acid production, the fermentation performance of microbial coculture was significantly improved.ConclusionsThe microbial coculture system constructed in this study demonstrated the strong potential of the process for the biosynthesis of valuable products from lignocellulosic hydrolysates containing high concentrations of complex inhibitors by specifically recruiting consortia of robust microorganisms with desirable characteristics and also provided a feasible and attractive method for the bioconversion of lignocellulosic biomass to other value-added biochemicals.
Highlights
Lignocellulosic biomass is an attractive and sustainable alternative to petroleum-based feedstock for the production of a range of biochemicals, and pretreatment is generally regarded as indispensable for its biorefinery
To exploit the effective utilization of lignocellulosic feedstocks by B. coagulans, undetoxified dilute acid-pretreated corn stover hydrolysate consisting of glucose (22.2 g/L), xylose (122 g/L), arabinose (~ 16 g/L), five carbohydrate degradation products, ten phenolic compounds and other unidentified inhibitors (Table 1) was used in this work
The hydrolysate was diluted to different concentrations (20, 30 and 40% (v/v)) and directly employed for lactic acid fermentation by B. coagulans NL01
Summary
Lignocellulosic biomass is an attractive and sustainable alternative to petroleum-based feedstock for the production of a range of biochemicals, and pretreatment is generally regarded as indispensable for its biorefinery. Biochemicals produced from renewable resources through microbial fermentation are rapidly garnering interest due to the exhaustion of fossil fuels and associated environmental issues [1] Among these biochemicals, lactic acid and its derivatives are increasingly important building blocks, which have broad applications in the food and chemical industries [2]. Many pretreatment studies have shown that various inhibitors that severely impede microbial growth and fermentation are inevitably formed during the deconstruction of lignocellulose, mainly organic acids, furan derivatives and phenolic compounds [7]. These inhibitors constitute a severe obstacle to the efficient use of lignocellulosic sugars and the effective production of biochemicals. Developing low-cost approaches and microorganisms to overcome barriers of inhibitors from biomass for fermentation would contribute to the scale-up and commercialization of lignocellulosic biorefineries
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