A complete industrial system for economical succinic acid production by Actinobacillus succinogenes

Abstract

An industrial fermentation system using lignocellulosic hydrolysate, waste yeast hydrolysate, and mixed alkali to achieve high-yield, economical succinic acid production by Actinobacillus succinogenes was developed. Lignocellulosic hydrolysate and waste yeast hydrolysate were used efficiently as carbon sources and nitrogen source instead of the expensive glucose and yeast extract. Moreover, as a novel method for regulating pH mixed alkalis (Mg(OH)₂ and NaOH) were first used to replace the expensive MgCO₃ for succinic acid production. Using the three aforementioned substitutions, the total fermentation cost decreased by 55.9%, and 56.4 g/L succinic acid with yield of 0.73 g/g was obtained, which are almost the same production level as fermentation with glucose, yeast extract and MgCO₃. Therefore, the cheap carbon and nitrogen sources, as well as the mixed alkaline neutralize could be efficiently used instead of expensive composition for industrial succinic acid production.

Introduction

The development of biorefineries has recently attracted increasing attention as a means of providing sustainable alternative solutions to convert renewable agricultural materials into numerous economically viable products (fuels, chemicals, and other target molecules) and offer competitive performance compared to traditional petrochemical refineries (Ji et al., 2009, Dorado et al., 2009, Lynd and Wyman, 1999). Many chemicals that could only be produced by chemical processes in the past could potentially be generated biologically from annually renewable resources (Ragauskas et al., 2006).

Microbial production of succinic acid is a good example. Interest in this bioprocess has been increasing recently due to that succinic acid could serve as a precursor to various commodity chemicals used in industries like adipic acid, 1,4-butanediol, tetrahydrofuran, N-methyl pyrrolidinone, 2-pyrrolidinone, succinate salts, gamma-butyrolactone, poly-butyrate succinate, polyamides, and various green solvents (McKinlay et al., 2007, Zheng et al., 2009). Succinic acid is traditionally manufactured from petrochemicals through expensive processes. The biologic production of succinic acid from renewable resources and the greenhouse gas CO₂ would alleviate the dependence on specialty chemical production from petroleum. However, bio-based succinic acid has not yet become competitive with petrochemical-based production, mainly because of high production costs (McKinlay et al., 2007, Song and Lee, 2006). There is therefore a need to develop a cost-effective process for succinic acid production from renewable resources.

Among succinic acid producers such as Actinobacillus succinogenes (Guettler et al., 1999), Anaerobiospirillum succiniciproducens (Lee et al., 2010), Mannheimia succiniciproducens (Lee et al., 2002), and recombinant Escherichia coli (Jantama et al., 2008), A. succinogenes not only could efficiently produce succinate (Mckinlay et al., 2007), but also could use a wide range of carbon sources, including lactose, xylose, arabinose, cellobiose, and other reduced sugars, to produce succinic acid as the major end product (Guettler et al., 1999, Van der Werf et al., 1997). The cost of carbon sources has been reduced by many renewable resources, such as straw (Zheng et al., 2009), corn fiber (Chen et al., 2010a), crop stalk wastes (Li et al., 2010c), whey (Wan et al., 2008), wheat (Dorado et al., 2009), and cane molasses (Liu et al., 2008b), all of which could be hydrolyzed into mixed sugars. The process of succinic acid production from lignocellulosic materials is economically attractive. In addition to carbon sources, nitrogen sources are also used to reduce the cost of succinic acid fermentation. Our previous research have shown that A. succinogenes NJ113 could use an enzymatic hydrolysate of spent yeast cells as a nitrogen source for succinic acid production in glucose-based and corn fiber hydrolysate-based media (Jiang et al., 2010, Chen et al., 2010a).

Succinic acid is an acid product. Large amounts of alkaline neutralizer are required to maintain the pH during succinic acid fermentation. The cost of alkaline neutralizer accounts for a significant portion of raw material costs. Majority of studies on succinic acid production have used MgCO₃ as alkaline neutralizer to achieve high product concentrations. Nevertheless, the cost of MgCO₃ supplementation is not practical for industrial succinic acid fermentation. In a previous study, our laboratory also investigated the replacement of MgCO₃ with Na₂CO₃, NaHCO₃, or NH₃·H₂O as alkaline neutralizer (Li et al., 2010a, Li et al., 2010b, Ye et al., 2010). However, this could only happen under low initial carbon source concentrations. There have been no reports regarding the use of mixed alkalis as alkaline neutralizer for regulating pH for succinic acid production.

In this study, mixed alkalis were first used as a novel method for regulating pH for succinic acid production. A complete industrial system using lignocellulose hydrolysate as the carbon source, waste yeast hydrolysate as the nitrogen source, and mixed alkali as the alkaline neutralizer to achieve high-yield, economical succinic acid production by A. succinogenes was developed.