A genomic perspective on the potential of Actinobacillus succinogenes for industrial succinate production

Abstract

BackgroundSuccinate is produced petrochemically from maleic anhydride to satisfy a small specialty chemical market. If succinate could be produced fermentatively at a price competitive with that of maleic anhydride, though, it could replace maleic anhydride as the precursor of many bulk chemicals, transforming a multi-billion dollar petrochemical market into one based on renewable resources. Actinobacillus succinogenes naturally converts sugars and CO2 into high concentrations of succinic acid as part of a mixed-acid fermentation. Efforts are ongoing to maximize carbon flux to succinate to achieve an industrial process.ResultsDescribed here is the 2.3 Mb A. succinogenes genome sequence with emphasis on A. succinogenes's potential for genetic engineering, its metabolic attributes and capabilities, and its lack of pathogenicity. The genome sequence contains 1,690 DNA uptake signal sequence repeats and a nearly complete set of natural competence proteins, suggesting that A. succinogenes is capable of natural transformation. A. succinogenes lacks a complete tricarboxylic acid cycle as well as a glyoxylate pathway, and it appears to be able to transport and degrade about twenty different carbohydrates. The genomes of A. succinogenes and its closest known relative, Mannheimia succiniciproducens, were compared for the presence of known Pasteurellaceae virulence factors. Both species appear to lack the virulence traits of toxin production, sialic acid and choline incorporation into lipopolysaccharide, and utilization of hemoglobin and transferrin as iron sources. Perspectives are also given on the conservation of A. succinogenes genomic features in other sequenced Pasteurellaceae.ConclusionsBoth A. succinogenes and M. succiniciproducens genome sequences lack many of the virulence genes used by their pathogenic Pasteurellaceae relatives. The lack of pathogenicity of these two succinogens is an exciting prospect, because comparisons with pathogenic Pasteurellaceae could lead to a better understanding of Pasteurellaceae virulence. The fact that the A. succinogenes genome encodes uptake and degradation pathways for a variety of carbohydrates reflects the variety of carbohydrate substrates available in the rumen, A. succinogenes's natural habitat. It also suggests that many different carbon sources can be used as feedstock for succinate production by A. succinogenes.

A Na+-coupled C4-dicarboxylate transporter (Asuc_0304) and aerobic growth of Actinobacillus succinogenes on C4-dicarboxylates

“…During anaerobic growth on glucose, the characteristic fermentation pattern of A. succinogenes was observed with succinate, formate and acetate as the major products (McKinlay et al, 2007a(McKinlay et al, , 2010McKinlay & Vieille, 2008) (Table 1). During anaerobic growth on fumarate, approximately two-thirds of the fumarate was reduced to succinate, whereas one-third was oxidized to acetate.…”

“…In agreement with the important role of succinate production, the genome of A. succinogenes codes for the enzymes of C 4 -dicarboxylate-related metabolic pathways, such as fumarate reductase, fumarase and phosphoenolpyruvate carboxylase (McKinlay et al, 2007a(McKinlay et al, , b, 2010McKinlay & Vieille, 2008). Most enzymes of anaerobic C 4 -dicarboxylate metabolism have been studied or the corresponding genes have been identified (Kim et al, 2004;McKinlay et al, 2007aMcKinlay et al, , 2010McKinlay & Vieille, 2008). Nothing is known, however, about the transport of the C 4 -dicarboxylates.…”

“…In the rumen, fibrous polysaccharides, oligosaccharides or sugars are abundant and fermented to organic acids by various fibre-digestive eukaryotes and bacteria (Russell & Rychlik, 2001). A. succinogenes is adapted to fermentation of sugars and contains only an incomplete citric acid cycle, lacking citrate synthase, isocitrate dehydrogenase and succinate dehydrogenase (Guettler et al, 1999;McKinlay et al, 2007aMcKinlay et al, , 2010. The carbohydrates are catabolized to short-chain organic acids, which are supplied to secondary fermenters and to the host animal.…”

The pentose phosphate pathway leads to enhanced succinic acid flux in biofilms of wild-type Actinobacillus succinogenes

“…Metabolic flux models, including the OPPP, were developed for glucose ( Figure 1A) and xylose ( Figure 1B) based on the established metabolic pathways and the genome of A.succinogenes (McKinlay et al, 2007;McKinlay et al, 2010;McKinlay and Vieille, 2008).…”

“…These pathways, together with glycolysis, generate sufficient reduction power in a closed-cycle to balance that which is required for succinate production without leading to by-product formation (Van Heerden and Nicol, 2013b). A. succinogenes has an incomplete TCA cycle and lacks a glyoxylate shunt (McKinlay et al, 2010), therefore by-product formation via fermentative pathways, particularly acetate and formate, is necessary to balance redox in succinate production.…”