Wednesday, April 2, 2025
4/2/2025
Synthetic Biology Approach in Engineered Algae for Improved Milk Fat Composition in Formula - Project Summary Formula provides nutrition to infants as a partial or complete substitute for human milk for working mothers or in situations like lactation failure or poor maternal health. The heavy reliance on infant formula in the U.S. is reflected by a National Immunization Survey which found that only ~25% of infants (< 6 months) were exclusively breastfed between 2018-19, a number that was even smaller in rural areas and low-income families. The fat composition of formulas serves a vital role in replacing human milk fat (HMF), which provides >50% of energy to the infant during early lactation. However, derived from vegetable oils, the fat in commercial formulas often lacks the unique fatty acid composition and lipid structure of HMF, resulting in reduced dietary benefits and poorer health outcomes for infants. The distinct features of HMF include but are not limited to 1) a substantial portion of medium-chain (C8:0-C14:0) fatty acids and 2) the prevalence at the sn-2 position of palmitic acid (a C16:0 fatty acid) on triacylglycerols (TAGs). Medium-chain fatty acids are desirable as a quick source of energy for infants because of their higher absorption rates compared to longer fatty acids. C16:0 esterification at the sn- 2 position prevents its release during digestion by the sn-1,3 lipase. This is important to avoid 16:0 precipitation, which chelates essential calcium ions and causes hard stools. Present methods for correcting fatty acid composition and TAG regioisomeric structure in formula are expensive and because of their reliance on palm oil, undesirable from an environmental perspective. This project addresses these challenges through the development of an HMF substitute in metabolically engineered algae: the goal is to generate a healthy, environmentally friendly, and low-cost product for US consumption. Auxenochlorella protothecoides (A.pro) presents an ideal platform for this goal because of 1) its exceptional biomass and oil accumulating capabilities compared to traditional oil crops, 2) convenient genetic and genome modification tools to facilitate metabolic engineering, and 3) the potential for producing the product at commercial scale. In this context, a fatty acid substrate pool resembling the fatty acid composition of HMF will be built by heterologous expression of chain length-determining fatty acyl-ACP thioesterases with desired substrate specificities (e.g., C8:0-C14:0) in A.pro, followed by GC-MS product analysis for assessment (Aim 1). To achieve TAG products with the correct regio- selectivity (C16:0 at sn-2), the C16:0-specific lysophosphatidic acid acyltransferase will be introduced, followed by stereochemical analysis of TAGs by sn-1,3 lipases treatment and GC-MS analysis of the isolated monoacylglycerols (Aim 2). Finally, the endogenous polycistronic gene expression system, discovered recently by the sponsor, will be exploited for simultaneous expression of rate-limiting enzymes in fatty acid biosynthesis, which will streamline the engineering process and enable more efficient production of HMF in A.pro (Aim 3). In summary, this research will explore the feasibility of producing HMF in oleaginous green algae for infant formula and also pave the way for developing a promising synthetic biology approach for other bioproducts in A.pro.
HHS’ Tracking Accountability in Government Grants System (TAGGS) website provides access to detailed descriptions of grants, loans, aggregated direct payments and other types of financial assistance awarded by the HHS Operating Divisions (OPDIVs) and the Office of the Secretary Staff Divisions (STAFFDIVs).