Internal Illumination to Overcome the Cell Density Limitation in the Scale-up of Whole-Cell Photobiocatalysis.

Markus Hobisch,Robert Kourist,Giovanni Davide Barone,Lenny Malihan‐Yap,Kathrin Castiglione,Selin Kara,Jelena Spasic,Paula Tamagnini

doi:10.1002/cssc.202100832

Abstract

Cyanobacteria have the capacity to use photosynthesis to fuel their metabolism, which makes them highly promising production systems for the sustainable production of chemicals. Yet, their dependency on visible light limits the cell‐density, which is a challenge for the scale‐up. Here, it was shown with the example of a light‐dependent biotransformation that internal illumination in a bubble column reactor equipped with wireless light emitters (WLEs) could overcome this limitation. Cells of the cyanobacterium Synechocystis sp. PCC 6803 expressing the gene of the ene‐reductase YqjM were used for the reduction of 2‐methylmaleimide to (R)‐2‐methylsuccinimide with high optical purity (>99 % ee). Compared to external source of light, illumination by floating wireless light emitters allowed a more than two‐fold rate increase. Under optimized conditions, product formation rates up to 3.7 mm h−1 and specific activities of up to 65.5 U gDCW −1 were obtained, allowing the reduction of 40 mm 2‐methylmaleimide with 650 mg isolated enantiopure product (73 % yield). The results demonstrate the principle of internal illumination as a means to overcome the intrinsic cell density limitation of cyanobacterial biotransformations, obtaining high reaction rates in a scalable photobioreactor.

Highlights

Photobiocatalysis has emerged as a new, exciting research area that combines photocatalysis and biocatalysis, two of the most research-intensive fields of catalysis.[1]
The specific activity of 180 μmol per hour and per mg chlorophyll a[10] consumes a considerable part of the total photo-production of nicotinamide adenine dinucleotide phosphate (NADPH) that has been estimated to be in the range of 530–1070 μmol mgchlaÀ 1 hÀ 1.[18]. In this article, we investigate the effect of internal illumination on the initial reaction rate and volumetric yield in the scale-up of a photobiocatalytic asymmetric enzymatic ene-reduction in recombinant cells of Synechocystis
Synechocystis PcpcB::yqjM was cultivated in 200 mL gas washing bottles under continuous light illumination reaching an optical density at 750 nm (OD750) of 1–3 (Supporting Information, Figure S3a), harvested and utilized in whole-cell light-driven reduction of 2-MM to (R)-2-methylsuccinimide (2-MS) (Figure 1a) with external illumination using light emitting diode (LED) lamps (200 μE mÀ 2 sÀ 1)

Summary

Introduction

Have been established with high reaction rates, the scale-up of the reaction requires a photobioreactor geometry with very short light penetration pathways. This reaction proceeds with high stereoselectivity and represents a typical stereoselective redox reaction for the synthesis of fine chemicals. The specific activity of 180 μmol per hour and per mg chlorophyll a (μmol mgchlaÀ 1 hÀ 1)[10] consumes a considerable part of the total photo-production of nicotinamide adenine dinucleotide phosphate (NADPH) that has been estimated to be in the range of 530–1070 μmol mgchlaÀ 1 hÀ 1.[18] In this article, we investigate the effect of internal illumination on the initial reaction rate and volumetric yield in the scale-up of a photobiocatalytic asymmetric enzymatic ene-reduction in recombinant cells of Synechocystis

Results and Discussion

Conclusion

Conflict of Interest