A new study explores the increased acetate biosynthesis in Synechocystis PCC 6803

A new study, supported by the PROMICON project, explores increased acetate biosynthesis in Synechocystis PCC 6803 and highlights promising advances in microbial acetate production. Acetate, a biological anion with numerous applications in the chemical and food industries, is commonly produced by microbial fermentation. In Synechocystis, acetate is generated through photosynthesis, utilising CO₂ and solar energy. However, wild-type Synechocystis strains produce only low levels of extracellular acetate.

A heterologous phosphoketolase (PKPa) enzyme was inserted into the acs locus, which encodes acetyl-CoA synthetase, responsible for converting acetate into acetyl-CoA. The engineered strain exhibited a 40-fold increase in acetate levels compared to wild-type cells. Metabolomic analysis revealed a faster Calvin-Benson-Bassham cycle, with increased levels of key metabolites such as glyceraldehyde 3-phosphate and fructose-1,6-bisphosphate. Acetyl-P and erythrose-4-phosphate levels also rose, while acetyl-CoA remained stable, suggesting efficient carbon turnover.

Examining the role of specific enzymes in acetate production showed that the overexpression of phosphotransacetylase (Pta) significantly boosted acetate production. Combined with PKPa insertion, the engineered strain produced up to 2.3 g/L of acetate after 14 days of cultivation, an 80-fold increase. These findings underscore the importance of metabolic engineering in enhancing microbial acetate biosynthesis, with implications for industrial applications and sustainable production processes.

Outline of the Calvin-Benson-Basshmam (CBB) cycle, carboxysome and the native acetate production pathway. The carboxysome is representing by the green hexagonal, the CBB cycle is represented by solid black lines while the inserted phosphoketolase is represented with solid blue lines.The intermediates are represented using abbreviations; 3PGA, 3-phosphoglycerate; G3P, glyceraldehyde-3-phosphate; DHAP, dihydroxyacetone phosphate; FBP, fructose-1,6-bisphosphate; SBP, sedoheptulose-1,7-bisphosphate; F6P, fructose-6-phosphate; S7P, sedoheptulose-7-phosphate; E4P, erythrose-4-phosphate; Xu5P, xylulose-5-phosphate; R5P, ribose-5-phosphate; Ru5P, ribulose-5-phosphate; RuBP, ribulose-1,5-bisphosphate. Enzymes; pta, phosphotransacetylase; acka, acetate kinase; acs, acetyl-CoA synthetase; ach; acetyl-CoA hydrolase and PK; phosphoketolase. With blue colour are highlighted the main substrates for acetate biosynthesis and with red the acetate is highlighted.