Membrane manipulation by free fatty acids improves microbial plant polyphenol synthesis.

Microbial synthesis of nutraceutically and pharmaceutically interesting plant polyphenols represents a more environmentally friendly alternative to chemical synthesis or plant extraction. However, most polyphenols are cytotoxic for microorganisms as they are believed to negatively affect cell integrity and transport processes. To increase the production performance of engineered cell factories, strategies have to be developed to mitigate these detrimental effects. Here, we examine the accumulation of the stilbenoid resveratrol in the cell membrane and cell wall during its production using Corynebacterium glutamicum and uncover the membrane rigidifying effect of this stilbenoid experimentally and with molecular dynamics simulations. A screen of free fatty acid supplements identifies palmitelaidic acid and linoleic acid as suitable additives to attenuate resveratrol's cytotoxic effects resulting in a three-fold higher product titer. This cost-effective approach to counteract membrane-damaging effects of product accumulation is transferable to the microbial production of other polyphenols and may represent an engineering target for other membrane-active bioproducts.

Process engineering of pH tolerant Ustilago cynodontis for efficient itaconic acid production.

BACKGROUND: Ustilago cynodontis ranks among the relatively unknown itaconate production organisms. In comparison to the well-known and established organisms like Aspergillus terreus and Ustilago maydis, genetic engineering and first optimizations for itaconate production were only recently developed for U. cynodontis, enabling metabolic and morphological engineering of this acid-tolerant organism for efficient itaconate production. These engineered strains were so far mostly characterized in small scale shaken cultures. RESULTS: In pH-controlled fed-batch experiments an optimum pH of 3.6 could be determined for itaconate production in the morphology-engineered U. cynodontis Δfuz7. With U. cynodontis ∆fuz7r ∆cyp3r PetefmttA Pria1ria1, optimized for itaconate production through the deletion of an itaconate oxidase and overexpression of rate-limiting production steps, titers up to 82.9 ± 0.8 g L-1 were reached in a high-density pulsed fed-batch fermentation at this pH. The use of a constant glucose feed controlled by in-line glucose analysis increased the yield in the production phase to 0.61 gITA gGLC-1, which is 84% of the maximum theoretical pathway yield. Productivity could be improved to a maximum of 1.44 g L-1 h-1 and cell recycling was achieved by repeated-batch application. CONCLUSIONS: Here, we characterize engineered U. cynodontis strains in controlled bioreactors and optimize the fermentation process for itaconate production. The results obtained are discussed in a biotechnological context and show the great potential of U. cynodontis as an itaconate producing host.

Engineering the morphology and metabolism of pH tolerant Ustilago cynodontis for efficient itaconic acid production.

Besides Aspergillus terreus and Ustilago maydis, Ustilago cynodontis is also known as a natural itaconate producer. U. cynodontis was reported as one of the best itaconate producing species in the family of the Ustilaginaceae, featuring a relatively high pH tolerance in comparison to other smut fungi. However, in contrast to U. maydis, it readily displays filamentous growth under sub-optimal growth conditions. In this study, U. cynodontis is established as efficient pH-tolerant itaconic acid producer through a combination of morphological and metabolic engineering. Deletions of the genes ras2, fuz7, and ubc3 abolished the filamentous growth of U. cynodontis, leading to a stable yeast-like growth under a range of stress-inducing conditions. The yeast-like morphology was also maintained in a pulsed fed batch production of 21 g L-1 itaconic acid and 9.3 g L-1 (S)-2-hydroxyparaconate at a pH of 3.8. The genetic and metabolic basis of itaconic acid production in U. cynodontis was characterized through comparative genomics and gene deletion studies. A hyper-producer strain was metabolically engineered using this knowledge resulting in a 6.5-fold improvement of titer.