The present disclosure relates to biosynthetic pathways for producing flavor and fragrance chemicals, such as green notes including trans-2-unsaturated aldehydes and lactones. The present disclosure provides methods for producing trans-2-unsaturated aldehydes, delta-lactones, and gamma-lactones. The present disclosure provides pathways for the preparation of trans-2-unsaturated aldehydes, delta-lactones, and gamma-lactones by reacting aldehydes in the presence of aldolases.

A non-naturally occurring microorganism having a 1,3-BDO pathway is provided. The microorganism expresses at least one of the following 1,3-BDO pathway enzymes: an aldolase that catalyzes condensation of two acetaldehydes to produce 3-hydroxybutanal; and an aldo-ketoreductase, oxidoreductase, aldehyde reductase or alcohol dehydrogenase that reduces 3-hydroxybutanal to 1,3-BDO. The organism may further express one or more enzymes for producing acetaldehyde. A biosynthetic process involves condensing two acetaldehyde molecules to 3-hydroxybutanal using an enzyme from class aldolases; and selectively reducing 3-hydroxybutanal to 1,3-BDO using an enzyme belonging to the class aldo-ketoreductase, oxidoreductase, aldehyde reductase or alcohol dehydrogenase. The process can further include producing acetaldehyde by a biosynthetic method.

Described is a method for the production of D-erythrose and acetyl phosphate comprising the enzymatic conversion of D-fructose into D-erythrose and acetyl phosphate by making use of a phosphoketolase. The produced D-erythrose can further be converted into glycolaldehyde by a method for the production of glycolaldehyde comprising the enzymatic conversion of D-erythrose into glycolaldehyde by making use of an aldolase, wherein said aldolase is a 2-deoxyribose-5-phosphate aldolase (EC 4.1.2.4) or a fructose-bisphosphate aldolase (EC 4.1.2.13). The produced glycolaldehyde can finally be converted into acetyl phosphate by the enzymatic conversion of the thus produced glycolaldehyde into acetyl phosphate by making use of a phosphoketolase or a sulfoacetaldehyde acetyltransferase.

The present invention provides engineered deoxyribose-phosphate aldolase polypeptides useful under industrial process conditions for the production of pharmaceutical and fine chemical compounds.

A method for producing 2,4-dihydroxybutyrate (DHB) or L-threonine using a microbial metabolic pathway is disclosed, by expressing the metabolic pathway in a microbial production strain which was previously modified with respect to its natural wild type form by introducing at least one of the genes necessary for the expression of those enzymes used for the enzymatic conversions into the production strain.