Efficient Bioproduction By Psychrophile-Based Simple Biocatalysts

Bioproduction of valuable chemicals by conventional biocatalysts are some problem to improve the yields and productivities. Metabolic modifications or fermentation regulations are required for whole cell biocatalysts to enhance the metabolic fluxes. Extracted enzymes can directly reacted with the substrate, however, these approach are often extremely laborious and costly.

              To conduct the effective bioproductions, psychrophile-based simple biocatalysts (PSCat) was developed to convert all substrate to products without byproduct formation. The approach is based on the expression of mesophilic enzymes in psychrophilic bacteria, which are then heat treated at moderate temperatures; as a result, intrinsic bacterial enzymes are inactivated, while recombinant mesophilic enzymes retain their catalytic activity. Thus, PSCat is expected to efficiently convert substrates into target compounds without the interference of by-products synthesized by natural bacterial enzymes.

              PSCat has been successfully applied to produce high yield of 3-hydroxypropionaldehyde (3-HPA) from glycerol by heat treatment at 45 °C. 3-HPA was stoichiometrically produced with the complete consumption of glycerol at a high production rate of 8.85 mmol 3-HPA/g dry cell/h. PSCat could convert biodiesel-derived crude glycerol to 3-HPA. PSCat has significant advantages over conventional methods in that it is easy to prepare and implement since the method only requires heat treatment of bacterial cells [1].

              PSCat could convert building-block chemicals such as aspartic acid which has been selected as a top value-added chemical from biomass by the US Department of Energy. Aspartic acid is produced by partially purified enzymes or whole bacteria including immobilized cells such as Escherichia coli bound to polyurethane carriers. However, in intact cells, a fraction of the fumaric acid was lost because of the activity of constitutively expressed bacterial fumarase that converts fumaric acid to L-malate. To generate an efficient biocatalyst by a simple procedure, PSCat was constructed by expressing E. coli aspartase in a psychrophilic bacterium, Shewanella livingstonensisAc10. PSCat treated with heat at 50°C for 15 min was produced aspartic acid without L-malic acid as a major byproduct. Furthermore, the immobilized PSCat with sodium alginate was repeatedly used for the conversion. The yield for nine reactions maintained over 97.5% as well as the immobilized extracted aspartase [2].

              PSCat also applied for fructose production from mannitol, the major component in marine biomass resource. PSCat expressed mannitol dehydrogenase and NADH oxidase was convert 50 mM mannitol to fructose with 97% yield, and fructose was not converted to further metabolites.

              We are trying to produce valuable chemicals with high yields by PSCat catalyzing multiple enzymatic reactions by constructing the strong gene expression tool. 

References

1. T. Tajima et al., AMB Express, 3(1), 69 (2013)
2. T. Tajima et al., Journal of Industrial Microbiology & Biotechnology, 42(10), 1319-1324, (2015)