A New Strategy for Effective Succinic Acid Production by Enterobacter sp. LU1 Using a Medium Based on Crude Glycerol and Whey Permeate

Abstract

The newly-isolated strain Enterobacter sp. LU1, which has previously been shown to be an effective producer of succinic acid on glycerol with the addition of lactose, was used for further intensive works aimed at improving the production parameters of the said process. The introduction of an initial stage of gentle culture aeration allowed almost 47 g/L of succinic acid to be obtained after 168 h of incubation, which is almost two times faster than the time previously taken to obtain this amount. Furthermore, the replacement of glycerol with crude glycerin and the replacement of lactose with whey permeate allowed the final concentration of succinic acid to be increased to 54 g/L. Considering the high content of yeast extract (YE) in the culture medium, tests were also performed with a reduced YE content via its partial substitution with urea. Although this substitution led to a deterioration of the kinetic parameters of the production process, using the fed-batch strategy, it allowed a succinic acid concentration of 69 g/L to be obtained in the culture medium, the highest concentration ever achieved using this process. Furthermore, the use of microaerophilic conditions meant that the addition of lactose to the medium was not required, with 37 g/L of succinic acid being produced on crude glycerol alone.

A Genomic Perspective on the Potential of Wild-Type Rumen Bacterium Enterobacter sp. LU1 as an Industrial Platform for Bio-Based Succinate Production

“…Glycerol is among the main waste feedstock generated in large amounts during biodiesel production [39]. It was experimentally confirmed that this waste product can be used efficiently by LU1 strain as a cheap carbon source in SA production under anaerobic conditions [1,15]. Thus, the genetic background of glycerol metabolism under these conditions has been deeply investigated.…”

“…In turn, pyruvate can be reduced to lactate due to the presence of ldhA (FZF21_18020) gene encoding lactate dehydrogenase (LDH), while acetyl-CoA can be transformed to acetate by both phosphate acetyltransferase (PTA) and acetate kinase (ACK) encoded by the pta (FZF21_17460) and ackA (FZF21_17465) genes, respectively, or reduced to ethanol by alcohol dehydrogenase (ADH) encoding by adhE (FZF21_20165) gene [42]. All of these genes have also been found in the LU1 strain genome, which explains the presence of byproducts such as lactate, acetate, and ethanol in the fermentation broth [1,15]. As reported by Yu et al [39], in E. coli, there is another glycerol utilization pathway under anaerobic conditions.…”

“…Because Enterobacter sp. LU1 was recognized as a highly efficient SA producer, the genetic background of putative biochemical routes for succinate formation were investigated [1,15]. There are three possible biochemical succinate formation pathways: (1) the reductive branch of the TCA cycle, (2) the glyoxylate pathway, and (3) the oxidative TCA cycle [17].…”

“…In turn, under semi-aerobic conditions it is possible to produce SA using glycerol alone. Moreover, it has been shown that aeration at an early stage of strain culturing resulted in faster growth of bacterial biomass [15]. This is an important feature, especially considering that many industrial strains are strictly anaerobic microorganisms that require rich culture media and the preservation of stringent anaerobic conditions during biomass growth and fermentation [17].…”

“…LU1 were carried out [1]. The strain has been shown to be able to efficiently produce SA utilizing valuable feedstocks, specifically crude glycerol and whey permeate derived from the petroleum and whey industries, respectively [15]. Under anaerobic conditions, succinate concentration in culture medium reached 69 g/L, while the final titer of SA under microaerophilic conditions on glycerol alone was 37 g/L [15].…”