Engineering Scheffersomyces segobiensis for palmitoleic acid-rich lipid production.

Palmitoleic acid (POA; C16:1) is an essential high-value ω-7-conjugated fatty acid with beneficial bioactivities and potential applications in the nutraceutical and pharmaceutical industries. Previously, the oleaginous yeast Scheffersomyces segobiensis DSM27193 has been identified as a promising production host as an alternative for POA extraction from plant or animal sources. Here, the POA-producing capacity of this host was further expanded by optimizing the fermentation process and molecular strain engineering. Specifically, a dual fermentation strategy (O-S dynamic regulation strategy) focused on the substrate and dissolved oxygen concentration was designed to eliminate ethanol and pyruvate accumulation during fermentation. Key genes influencing POA production, such as jen, dgat, ole were identified on the transcriptional level and were subsequently over-expressed. Furthermore, the phosphoketolase (Xpk)/phosphotransacetylase (Pta) pathway was introduced to improve the yield of the precursor acetyl-CoA from glucose. The resulting cell factory SS-12 produced 7.3 g/L of POA, corresponding to an 11-fold increase compared to the wild type, presenting the highest POA titre reported using oleaginous yeast to date. An economic evaluation based on the raw materials, utilities and facility-dependent costs showed that microbial POA production using S. segobiensis can supersede the current extraction method from plant oil and marine fish. This study reports the construction of a promising cell factory and an effective microbial fermentation strategy for commercial POA production.

Biodegradation of polyester polyurethane by Cladosporium sp. P7: Evaluating its degradation capacity and metabolic pathways.

Microorganisms capable of decomposing polyurethane (PU) and other plastics have the potential to be used in bio-recycling processes. In this study, 20 PU-degrading strains were isolated, including 11 bacteria and 9 fungi, using a synthesized poly(1,4-butylene adipate)-based PU (PBA-PU) as the screening substrate. Three PU substrates with increasing structure complexities were used for a thorough evaluation of microbial degradation capacity: Impranil® DLN-SD, PBA-PU film and PU foam waste. After 4 days, the best fungal PBA-PU degrader, Cladosporium sp. P7, could degrade 94.5% of Impranil® DLN-SD. After 28 days of cultivation, 32.42% and 43.91% of solid PBA-PU film was converted into soluble small molecules when used as the sole carbon source or in a medium with other co-carbon sources, respectively. Accordingly, the weight loss of PU foam waste after 15 days was 15.3% for the sole carbon condition and 83.83% for the co-carbon conditions. Furthermore, PBA-PU was used for metabolic pathway analysis because of its known composition and chemical structure. Six metabolites were identified during the degradation process of PBA-PU, including adipic acid (AA), 1,4-butanediol (BDO), and 4,4'-methylenedianiline (MDA), which can also be used as the sole carbon source to grow the fungal strain P7, resulting in the discovery of two MDA metabolites during the cultivation processes. Based on the presence of these eight metabolites, we hypothesized that PBA-PU is first depolymerized by the fungal strain P7 via ester and urethane bond hydrolysis, followed by intracellular metabolism and mineralization of the three monomers to CO2 and H2O.