Novel routes for bioproduction of delta lactone aroma compounds

Delta lactones are fatty acid-derived aroma compounds that hold tremendous commercial value. As consumer demand for natural flavours continues to rise, the bioproduction of δ-lactones, including δ-decalactone and δ-dodecalactone, is attracting substantial interest. Our study brings forth a novel approach to the bioproduction of δ-lactones from glucose, deviating from existing methods that primarily rely on the biotransformation of fatty acids. The high cost of fatty acid raw material constrains the commercial viability of this traditional approach. We engineered surface-lipid producing type I polyketide synthase (PKS) from Mycobacterium smegmatis by incorporating macrolactone thioesterase (TE) domain. Two out of three fusion constructs produced an appropriately engineered PKS-TE fusion protein that facilitated the synthesis of δ-lactones. When grown on glucose as the sole carbon source, recombinant E. coli expressing the engineered PKS-TE fusion protein successfully made δ-lactones ranging from C8-C18 acyl chains. Our research further highlights the potential of Mycobacterium smegmatis as a cell factory for producing fatty acid-based δ-lactones. By genetically designing and engineering Mycobacterium smegmatis to express PKS-TE fusion protein, we achieved bioproduction of various δ-lactones. Batch fermentation of the engineered E. coli strain fed with 2 % glucose produced 786 mg/L of δ-dodecalactone and 444 mg/L of δ-decalactone at 120 h, underscoring the efficacy of our approach. Thus, this study is the first to demonstrate a methodology for redirecting primary metabolic intermediates towards δ-lactone biosynthesis in engineered bacteria, enabling the use of inexpensive and renewable feedstocks.