MICROBIAL PRODUCTION

Bio-processing Requirements to Manufacture 1, 3-propanediol

Bio-processing Requirements to Manufacture 1, 3-propanediol

Introduction

The molecule chosen to be produced is 1, 3-propanediol using microbial fermentation. 1,3-Propanediol is one of the oldest known fermentation products. It was reliably identified as early as in 1881 by August Freund, inaglycerol fermentation mixed culture containing Clostridium pasteurianum as an active organism. It is a versatile intermediate compound used in the synthesis of heterocycles.Due to the presence of two hydroxyl groups at 1 and 3 positions, it finds applications in the production of polymers, such as polyesters and polyurethanes (Biebl et al., 2010: 154). Polymers based on 1,3-propanediol are more resistant to strains and has better washfastness. The production of new polyster, polytrimethylene terephthalate (PTT) has caused a drastic rise in the demand of 1,3- propanediol due to its superior stretching and stretch recovery characteristics (Kurian, 2009: 154). PPT is a biodegradable polymer which finds great potential in textile, carpets and upholstery manufacturing (Witt et al., 2011: 68). The synthesis of PTT is depicted in Fig. 1.

Figure 1

1,3-Propanediol (trimetylene glycol) has traditionally been considered as a 'specialty chemical' is now undergoing a transition into a 'commodity chemical' (Sheldon et al., 2010: 233). In recent years technological breakthroughs in the preparation of 1,3-propanediol have resulted in lower market prices, currently in the $0.80 per pound range. The market for 1,3-propanediol is currently over 100 million pounds per year and is growing rapidly (Kraus, 2008: 85).

Microorganisms producing 1,3-propanediol

Lately, considerable attention is being paid to the production of bulk chemicals from microorganisms. However, the production of 1,3- propanediol has only been known from bacteria (Biebl et al., 2010: 154). A number of microorganisms can ferment sugars to glycerol but they cannot convert glycerol to 1,3-propanediol. Others may have the ability to ferment glycerol to 1,3-propanediol and still others can ferment mixtures of glycerol and sugars to 1,3-propanediol, however, none can ferment sugars directly to 1,3-propanediol (Cameron et al., 2009: 166). There are reports where new metabolic pathways have been designed in cells by combining the ability to ferment sugar to glycerol and subsequently glycerol to 1,3-propanediol.

Enzymes involved in 1,3-propanediol production

The enzymes of glycerol metabolism are glycerol dehydratase (GDHt), 1,3-propanediol oxidoreductase (PDOR), glycerol dehydrogenase (GDH) and dihydroxyacetone phosphate kinase (DHAK). dissimilation involves two parallel pathways: reductive and oxidative. The reductive pathway is carried out in two enzymatic steps. The first enzyme Vitamin B12-dependent GDHt removes a water molecule from glycerol to form 3-hydroxypropionaldehyde (3-HPA), which is then reduced to 1,3-propanediol by second enzyme, NADHlinked PDOR. On the other hand, in the oxidative pathway glycerol is dehydrogenated to dihydroxyacetone (DHA) by a NAD+-linked GDH, then to dihydroxyacetone phosphate (DHAP) by an ATP-dependent DHAK (Forage and Lin, 2011) (Fig. 2).

Figure 2

Different strategies for the production of 1,3-propanediol

1,3-Propanediol is a typical product of glycerol fermentation and is not produced in anaerobic conversion of any other organic substrate. Various strategies to utilize renewable feedstocks are important to the future competitiveness of the industry. In this context, different strategies have been evaluated to produce 1,3-propanediol ...