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Succinic acid (SA) is one of the top candidate value-added chemicals that can be produced from biomass via microbial fermentation. A considerable number of cell factories have been proposed in the past two decades as native as well as non-native SA producers. Actinobacillus succinogenes is among the best and earliest known natural SA producers. However, its industrial application has not yet been realized due to various underlying challenges. Previous studies revealed that the optimization of environmental conditions alone could not entirely resolve these critical problems. On the other hand, microbial in silico metabolic modeling approaches have lately been the center of attention and have been applied for the efficient production of valuable commodities including SA. Then again, literature survey results indicated the absence of up-to-date reviews assessing this issue, specifically concerning SA production. Hence, this review was designed to discuss accomplishments and future perspectives of in silico studies on the metabolic capabilities of SA producers. Herein, research progress on SA and A. succinogenes, pathways involved in SA production, metabolic models of SA-producing microorganisms, and status, limitations and prospects on in silico studies of A. succinogenes were elaborated. All in all, this review is believed to provide insights to understand the current scenario and to develop efficient mathematical models for designing robust SA-producing microbial strains. [ABSTRACT FROM AUTHOR]

In this study, a novel biorefinery concept of succinic acid (SA) production from fruit and vegetable wastes (FVWs) hydrolyzed by crude enzyme mixtures through solid state fermentation was designed. Enzyme complex solid mashes from various types of FVWs were on-site produced through solid-state fermentation by Aspergillus niger and Rhizopus oryzae . This solid was then added to FVW suspensions and undergo hydrolysis reaction to generate fermentable sugars and other essential nutrients for bacterial growth and product formation. The subsequent fungal hydrolysis produced 12.00 g/L glucose and 13.83 g/L fructose using 10% mass ratio (w/v) of FVW. Actinobacillus succinogenes used this FVW hydrolysate as the sole feedstock and produced 27.03 g/L of succinic acid with high yield and productivity of 1.18 g SA/g sugar and 1.28 gL −1 h −1 , respectively. This work demonstrated that FVWs can be biotransformed to value added products which have considerable potential economics and environmental meaning. [ABSTRACT FROM AUTHOR]

• Tolerance level of A. succinogenes against HMF and furfural was scrutinized. • Inhibitory effect was investigated using single and mixed sugars. • A. succinogenes showed more tolerance against HMF than furfural. • Synergetic effect of inhibitors was severe relative to individual inhibitor. • A. succinogenes exhibited more preference to glucose than xylose. Pretreatment is crucial step to overcome the stiffness of lignocellulosic materials so as to make sugars available for subsequent enzymatic hydrolysis and microbial fermentation. Unfortunately, commonly used pretreatment methods cause formation of various toxic degradation products that have inhibitory effect on growth and fermentation. Hydroxymethylfurfural (HMF) and furfural are furan derivative inhibitors generated via degradation of hexoses and pentoses, respectively. In this study, inhibitory effects of HMF and furfural (0–10 g/L) on succinic acid producing Actinobacillus succinogenes were investigated using lignocellulosic model sugars of glucose and xylose. To this end, A. succinogenes attained explicable level of tolerance against these inhibitors but better performance with HMF than furfural. Nevertheless, synergetic effect of these inhibitors was severer compared with individual one. Overall, this study could provide vital notions to understand strain's tolerance level, and thereby helps to apply efficient pretreatment methods, utilize appropriate substrates, and develop robust biocatalysts. [ABSTRACT FROM AUTHOR]