One-Pot Biocatalytic Route from Alkanes to α,ω-Diamines by Whole-Cell Consortia of Engineered Yarrowia lipolytica and Escherichia coli

Metabolically engineered microbial consortia can contribute as a promising production platform for the supply of polyamide monomers. To date, the biosynthesis of long-chain α,ω-diamines from n-alkanes is challenging because of the inert nature of n-alkanes and the complexity of the overall synthesis pathway. We combined an engineered Yarrowia lipolytica module with Escherichia coli modules to obtain a mixed strain microbial consortium that could catalyze an efficient biotransformation of n-alkanes into corresponding α,ω-diamines. The engineered Y. lipolytica strain was constructed (YALI10) wherein the two genes responsible for β-oxidation and the five genes responsible for the overoxidation of fatty aldehydes were deleted. This newly constructed YALI10 strain expressing transaminase (TA) could produce 0.2 mM 1,12-dodecanediamine (40.1 mg/L) from 10 mM n-dodecane. The microbial consortia comprising engineered Y. lipolytica strains for the oxidation of n-alkanes (OM) and an E. coli amination module (AM) expressing an aldehyde reductase (AHR) and transaminase (TA) improved the production of 1,12-diamine up to 1.95 mM (391 mg/L) from 10 mM n-dodecane. Finally, combining the E. coli reduction module (RM) expressing a carboxylic acid reductase (CAR) and an sfp phosphopantetheinyl transferase with OM and AM further improved the production of 1,12-diamine by catalyzing the reduction of undesired 1,12-diacids into 1,12-diols, which further undergo amination to give 1,12-diamine as the target product. This newly constructed mixed strain consortium comprising three modules in one pot gave 4.1 mM (41%; 816 mg/L) 1,12-diaminododecane from 10 mM n-dodecane. The whole-cell consortia reported herein present an elegant "greener" alternative for the biosynthesis of various α,ω-diamines (C8, C10, C12, and C14) from corresponding n-alkanes.

New Aspects on the Direct Solid State Polycondensation (DSSP) of Aliphatic Nylon Salts: The Case of Hexamethylene Diammonium Dodecanoate

The direct solid state polymerization (DSSP) of hexamethylene diammonium dodecanoate (PA 612 salt) was investigated for two different salt grades, fossil-based and bio-based. Aliphatic polyamide salts (such as PA 612 salt) are highly susceptible to solid melt transition (SMT) phenomena, which restrain the industrial application of DSSP. To that end, emphasis was given on reactor design, being the critical parameter influencing byproduct diffusion, amine loss and inherent DSSP kinetics. Experiments took place both at the microscale and the laboratory scale, in which two different reactors were tested in terms of bypassing SMT phenomena. The new reactor designed here proved quite successful in maintaining the solid state during the reaction. Scouting experiments were conducted in order to assess the effect of critical parameters and determine appropriate reaction conditions. Fossil-based PA 612 products proved to have a better end-group imbalance in comparison to bio-based ones, which is critical in terms of achieving high molecular weight. Finally, a real DSSP process was demonstrated, starting from PA 612 salt crystals and ending with PA 612 particles.

Assessing the Conversion of Various Nylon Polymers in the Hydrothermal Liquefaction of Macroalgae

Marine macroalgae offers a promising third generation feedstock for the production of fuels and chemicals, avoiding competition with conventional agriculture and potentially helping to improve eutrophication in seas and oceans. However, an increasing amount of plastic is distributed into the oceans, and as such contaminating macroalgal beds. One of the major plastic contaminants is nylon 6 derived from discarded fishing gear, though an increasing amount of alternative nylon polymers, derived from fabrics, are also observed. This study aimed to assess the effect of these nylon contaminants on the hydrothermal liquefaction of Fucus serratus. The hydrothermal liquefaction (HTL) of macroalgae was undertaken at 350 °C for 10 min, with a range of nylon polymers (nylon 6, nylon 6/6, nylon 12 and nylon 6/12), in the blend of 5, 20 and 50 wt.% nylon to biomass; 17 wt.% biocrude was achieved from a 50% blend of nylon 6 with F. serratus. In addition, nylon 6 completely broke down in the system producing the monomer caprolactam. The suitability of converting fishing gear was further demonstrated by conversion of actual fishing line (nylon 6) with the macroalgae, producing an array of products. The alternative nylon polymer blends were less reactive, with only 54% of the nylon 6/6 breaking down under the HTL conditions, forming cyclopentanone which distributed into the biocrude phase. Nylon 6/12 and nylon 12 were even less reactive, and only traces of the monomer cyclododecanone were observed in the biocrude phase. This study demonstrates that while nylon 6 derived from fishing gear can be effectively integrated into a macroalgal biorefinery, alternative nylon polymers from other sectors are too stable to be converted under these conditions and present a real challenge to a macroalgal biorefinery.