Microbial production of 1,3-propanediol: Recent developments and emerging opportunities

1,3-Propanediol, a valuable bifunctional molecule, can be produced from renewable resources using microorganisms. It has several promising properties for many synthetic reactions, particularly for polymer and cosmetic industries. By virtue of being a natural product, relevant biochemical pathways can be harnessed into fermentation processes to produce 1,3-propanediol. Various strategies for the microbial production of 1,3-propanediol are reviewed and compared in this article with their promises and constraints. Furthermore, genetic and metabolic engineering could significantly improve product yields and overcome the limitations of fermentation technology. Present review gives an overview on 1,3-propanediol production by wild and recombinant strains. It also attempts to encompass the various issues concerned in utilization of crude glycerol for 1,3-propanediol production, with particular emphasis laid on biodiesel industries. This review also summarizes the present state of strategies studied for the downstream processing and purification of biologically produced 1,3-propanediol. The future prospect of 1,3-propanediol and its potential as a major bulk chemical are discussed under the light of the current research.     

Role of the support surface on the loading and the activity of Pseudomonas fluorescens lipase used for biodiesel synthesis

The present work investigates the influence of the support surface on the loading and the enzymatic activity of the immobilized Pseudomonas fluorescens lipase. Different porous materials, polypropylene (Accurel), polymethacrylate (Sepabeads EC-EP), silica (SBA-15 and surface modified SBA-15), and an organosilicate (MSE), were used as supports. The immobilized biocatalysts were compared towards sunflower oil ethanolysis for the sustainable production of biodiesel. Since the supports have very different structural (ordered hexagonal and disordered) and textural features (surface area, pore size, and total pore volume), in order to consider only the effect of the support surface, experiments were performed at low surface coverage. The different functional groups occurring on the support surface allowed either physical (Accurel, MSE, and SBA-15) or chemical adsorption (Sepabeads EC-EP and SBA-15–R-CHO). The surface-modified SBA-15 (SBA-15–R-CHO) allowed the highest loading. The lipase immobilized on the MSE was the most active biocatalyst. However, in terms of catalytic efficiency (activity/loading) the lipase immobilized on the SBA-15, the support that allowed the lowest loading, was the most efficient.     

Esterification using a liquid lipase to remove residual free fatty acids in biodiesel

Lately, the price of liquid formulated lipase enzymes, usable in biodiesel production, has been significantly reduced. This enables one-time use of these enzymes for transesterification, and the process is used industrially. However, the process suffers a drawback by leaving 2−3 % free fatty acids in the crude biodiesel, which reduces the profitability. This article discusses a novel enzymatic FFA esterification reaction utilizing liquid lipase B from Candida antarctica (CALB) along with glycerol at low water concentrations to eliminate the residual FFA. The reaction setup was found able to reduce the free fatty acid concentration to within biodiesel specifications of < 0.25 wt.% FFA. Additionally, two alternative process setups are proposed, which were both found viable through a combination of experiments and simulations, and can be developed into full-scale processes. The resulting two-step enzymatic biodiesel process - transesterification followed by esterification - provides a potential process layout for the industrial production of biodiesel.     

Biodiesel production and optimization from Calophyllum inophyllum linn oil (honne oil) – A three stage method

The present work examines the production of a biodiesel from a non-edible oil namely honne oil (Calophyllum inophyllum linn). A three stage process viz., pre-treatment, alkali catalyzed transesterification and post treatment adopted for the production is discussed. The reaction parameters such as methanol to oil molar ratio, catalyst concentration, temperature and time have been optimized for the production of biodiesel. The yield of biodiesel from the honne oil under the optimized conditions is found to be 89%.     

High‐Performance and Stable All‐Polymer Solar Cells Using Donor and Acceptor Polymers with Complementary Absorption

To explore the advantages of emerging all‐polymer solar cells (all‐PSCs), growing efforts have been devoted to developing matched donor and acceptor polymers to outperform fullerene‐based PSCs. In this work, a detailed characterization and comparison of all‐PSCs using a set of donor and acceptor polymers with both conventional and inverted device structures is performed. A simple method to quantify the actual composition and light harvesting contributions from the individual donor and acceptor is described. Detailed study on the exciton dissociation and charge recombination is carried out by a set of measurements to understand the photocurrent loss. It is unraveled that fine‐tuned crystallinity of the acceptor, matched donor and acceptor with complementary absorption and desired energy levels, and device architecture engineering can synergistically boost the performance of all‐PSCs. As expected, the PBDTTS‐FTAZ:PNDI‐T10 all‐PSC attains a high and stable power conversion efficiency of 6.9% without obvious efficiency decay in 60 d. This work demonstrates that PNDI‐T10 can be a potential alternative acceptor polymer to the widely used acceptor N2200 for high‐performance and stable all‐PSCs.     

Methanol-free biosynthesis of fatty acid methyl ester (FAME) in Synechocystis sp. PCC 6803

To meet the increasing global demand of biodiesel over the next decades, alternative methods for producing one of the key constituents of biodiesel (e.g. fatty acid methyl esters (FAMEs)) are needed. Algal biodiesel has been a long-term target compromised by excessive costs for harvesting and processing. In this work, we engineered cyanobacteria to convert carbon dioxide into excreted FAME, without requiring methanol as a methyl donor. To produce FAME, acyl-ACP, a product of the fatty acid biosynthesis pathway, was first converted into free fatty acid (FFA) by a thioesterase, namely ’UcFatB1 from Umbellularia californica. Next, by employing a juvenile hormone acid O-methyltransferase (DmJHAMT) from Drosophila melanogaster and S-adenosylmethionine (SAM) as a methyl donor, FFAs were converted into corresponding FAMEs. The esters were naturally secreted extracellularly, allowing simple product separation by solvent overlay as opposed to conventional algae biodiesel production where the algae biomass must first be harvested and processed for transesterification of extracted triacylglycerols (TAGs). By optimizing both the promoter and RBS elements, up to 120 mg/L of FAMEs were produced in 10 days. Quantification of key proteins and metabolites, together with constructs over-expressing SAM synthetase (MetK), indicated that ’UcFatB1, MetK, and DmJHAMT were the main factors limiting pathway flux. In order to solve the latter limitation, two reconstructed ancestral sequences of DmJHAMT were also tried, resulting in strains showing a broader methyl ester chain-length profile in comparison to the native DmJHAMT. Altogether, this work demonstrates a promising pathway for direct sunlight-driven conversion of CO₂ into excreted FAME.     

Application of multi-component reaction for covalent immobilization of two lipases on aldehyde-functionalized magnetic nanoparticles; production of biodiesel from waste cooking oil

Lipase from Rhizomucor miehei (RML) and Thermomyces lanuginosa lipase (TLL) were immobilized on silica core-shell magnetic nanoparticles (Fe₃O₄@SiO₂) produced by coating Fe₃O₄ core with silica shell. The nanoparticles were functionalized with aldehyde groups followed by immobilization of RML and TLL by using a multi-component reaction in an extremely mild condition. Rapid immobilization of both enzymes (1.5−12 h) with high immobilization yields (81–100%) was observed. The maximum loading capacity of the support was determined to be 81 mg for RML and 97 mg for TLL. The thermal stability of the immobilized derivatives of RML and TLL were greatly improved by retaining 54 and 97 % of their initial activities at 65 °C, respectively. The immobilized preparations were used to produce biodiesel by transesterification of waste cooking oil. In an optimization study, Response Surface Methodology (RSM) and a central composite rotatable design (CCRD) were used to study the effect of amount of biocatalyst, temperature, reaction time, water adsorbent (wt.%) and ratio of t-butanol to oil (wt.%) on the yield of biodiesel production. Biodiesel production yield by immobilized TLL reached 93.1 % under optimal conditions while the maximum yield for RML was 57.5 %. Both immobilized derivatives showed high reusability after 5 cycles of the reaction.     

Study of biodiesel production from animal fats with high free fatty acid content

The aim of this work was to obtain biodiesel from animal fats, an inedible feedstock. Three different types of fats were used to produce biodiesel; their main characteristic was high free fatty acid content. Animal fats were transesterified with acid catalyst and basic catalyst with and without pre-esterification. Biodiesel of 89.0 wt.% ester content was obtained by acid-transesterification (9 wt.% H₂SO₄, 6:1 methanol:fats molar ratio, 60 °C, 48 h). Pre-esterification conditions were studied for different fats and acid catalysts: 0.5 wt.% H₂SO₄ or 1.0 wt.% p-TsOH, 6:1 methanol:fats molar ratio, 65 °C and 4 h made it possible to obtain fats with acid value less than 0.5% FFA. Pre-treatment was effective for fats with different FFA content. Alkali transesterification of esterified fats resulted in a product with 97.3 wt.% ester content. Biodiesel quality was evaluated and most of properties were well within EN 14214.     

Efficient lipid production with Trichosporon fermentans and its use for biodiesel preparation

Effects of medium components and culture conditions on biomass and lipid production of Trichosporon fermentans were studied. The optimal nitrogen source, carbon source and C/N molar ratio were peptone, glucose and 163, respectively. The favorable initial pH of the medium and temperature were 6.5 and 25 degrees C. Under the optimized conditions, a biomass of 28.1 g/l and a lipid content of 62.4% could be achieved after culture for 7 days, which were much higher than the original values (19.4 g/l and 50.8%) and the results reported by other groups. T. fermentans could grow well in pretreated waste molasses and a lipid yield of 12.8 g/l could be achieved with waste molasses of 15% total sugar concentration (w/v) at pH 6.0, representing the best result with oleaginous microorganisms on agro-industrial residues. Addition of various sugars to the pretreated molasses could efficiently enhance the accumulation of lipid and the lipid content reached as high as above 50%. Similar to vegetable oils, the lipid mainly contains palmitic acid, stearic acid, oleic acid and linoleic acid and the unsaturated fatty acids amount to about 64% of the total fatty acids. The microbial oil with an acid value of 5.6 mg KOH/g was transesterified to biodiesel by base catalysis after removal of free fatty acids and a high methyl ester yield of 92% was obtained.