Physiological characterization and quantitative proteomic analyses of metabolically engineered E. coli K4 strains with improved pathways for capsular polysaccharide biosynthesis.

Among capsulated bacteria, some produce polysaccharides with unique properties that have been shown to possess relevant industrial applications and commercial value. The capsular polysaccharide (CPS) produced by Escherichia coli K4 is similar to chondroitin sulphate, and recent efforts focused on the development of genetic and fermentation strategies to increase its production titers up to technologically attractive levels. However, the control of the metabolic pathways leading to CPS synthesis together with the effect of varying the concentration of pathway intermediates on CPS final titers, is still quite unexplored, and not fully understood. In the present study four genes involved in the biosynthesis of UDP-sugar CPS precursors, namely kfoA, kfoF, pgm, and galU, were overexpressed in different combinations, and diversely affected the biosynthetic machinery. At the physiological level, results revealed a central role for kfoF, coding for UDP-glucose dehydrogenase, that increased CPS production mostly. In the attempt to unravel the molecular mechanisms regulating CPS biosynthesis, an in depth analysis of the proteome of the recombinant strains overexpressing respectively pgm and galU, and pgm, galU, and kfoF was performed and compared to the wild-type. Although, interestingly, in both strains the impact of the genetic manipulation seemed rather limited at the proteome level, results obtained from the triple mutant indicated a crosstalk between the two pathways leading to UDP-sugar precursors biosynthesis, and also an unexpected link with the purine biosynthetic pathway. Overall our results present new insights into the role of metabolic intermediates for the formation of capsular polysaccharides, utilizing a systematic approach of metabolic engineering, combined with state-of-the-art quantitative proteomic approaches, as well as genetic and physiological information.

Production of succinic acid from Basfia succiniciproducens up to the pilot scale from Arundo donax hydrolysate.

In the present work the recently isolated strain Basfia succiniciproducens BPP7 was evaluated for the production of succinic acid up to the pilot fermentation scale in separate hydrolysis and fermentation experiments on Arundo donax, a non-food dedicated energy crop. An average concentration of about 17g/L of succinic acid and a yield on consumed sugars of 0.75mol/mol were obtained demonstrating strain potential for further process improvement. Small scale experiments indicated that the concentration of acetic acid in the medium is crucial to improve productivity; on the other hand, interestingly, short-term (24h) adaptation to higher acetic acid concentrations, and strain recovery, were also observed.

Engineering a branch of the UDP-precursor biosynthesis pathway enhances the production of capsular polysaccharide in Escherichia coli O5:K4:H4.

Escherichia coli K4 produces a capsule with a chemical structure that resembles chondroitin, a molecule with established chondro protective properties. The endogenous genes pgm and galU are involved in the biosynthesis of UDP-glucose which is a critical intermediate in carbohydrate metabolism and biochemical precursor of UDP-glucuronic acid. Together with UDP-N-acetylgalactosamine, UDP-glucuronic acid is used as sugar donor for capsule biosynthesis. The aim of the study was to evaluate how a change in the pathways leading to UDP-glucuronic acid biosynthesis affected capsular polysaccharide production. One additional copy of pgm and galU was introduced in E. coli K4 and in the previously described recombinant strain EcK4r3. A microbioreactor was used to analyse strain performance with parallel batch experiments, demonstrating increased polysaccharide concentrations and providing data that are comparable to those obtained in larger fermenters. Further experiments on a glutamine enriched medium showed an additional 45% increase of capsule production, maybe indicating the need to balance both branches leading to polymer biosynthesis in order to maximize yields. In the effort towards the establishment of a feasible bio-chondroitin production process this study provides information on how the availability of sugar precursors impacts polysaccharide biosynthesis in E. coli K4, a complex unexplored aspect of a multifaceted process.