RESUMO
Microbial fermentation of renewable feedstocks into plastic monomers can decrease our fossil dependence and reduce global CO2 emissions. 3-Hydroxypropionic acid (3HP) is a potential chemical building block for sustainable production of superabsorbent polymers and acrylic plastics. With the objective of developing Saccharomyces cerevisiae as an efficient cell factory for high-level production of 3HP, we identified the ß-alanine biosynthetic route as the most economically attractive according to the metabolic modeling. We engineered and optimized a synthetic pathway for de novo biosynthesis of ß-alanine and its subsequent conversion into 3HP using a novel ß-alanine-pyruvate aminotransferase discovered in Bacillus cereus. The final strain produced 3HP at a titer of 13.7±0.3gL(-1) with a 0.14±0.0C-molC-mol(-1) yield on glucose in 80h in controlled fed-batch fermentation in mineral medium at pH 5, and this work therefore lays the basis for developing a process for biological 3HP production.
Assuntos
Bacillus cereus , Proteínas de Bactérias , Ácido Láctico/análogos & derivados , Engenharia Metabólica , Saccharomyces cerevisiae , beta-Alanina-Piruvato Transaminase , Bacillus cereus/enzimologia , Bacillus cereus/genética , Proteínas de Bactérias/biossíntese , Proteínas de Bactérias/genética , Ácido Láctico/biossíntese , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , beta-Alanina/genética , beta-Alanina/metabolismo , beta-Alanina-Piruvato Transaminase/biossíntese , beta-Alanina-Piruvato Transaminase/genéticaRESUMO
Biologically produced 3-hydroxypropionic acid (3 HP) is a potential source for sustainable acrylates and can also find direct use as monomer in the production of biodegradable polymers. For industrial-scale production there is a need for robust cell factories tolerant to high concentration of 3 HP, preferably at low pH. Through adaptive laboratory evolution we selected S. cerevisiae strains with improved tolerance to 3 HP at pH 3.5. Genome sequencing followed by functional analysis identified the causal mutation in SFA1 gene encoding S-(hydroxymethyl)glutathione dehydrogenase. Based on our findings, we propose that 3 HP toxicity is mediated by 3-hydroxypropionic aldehyde (reuterin) and that glutathione-dependent reactions are used for reuterin detoxification. The identified molecular response to 3 HP and reuterin may well be a general mechanism for handling resistance to organic acid and aldehydes by living cells.