Photosynthetically produced sucrose by immobilized Synechocystis sp. PCC 6803 drives biotransformation in E. coli

Abstract

Background Whole-cell biotransformation is a promising emerging technology for the production of chemicals. When using heterotrophic organisms such as E. coli and yeast as biocatalysts, the dependence on organic carbon source impairs the sustainability and economic viability of the process. As a promising alternative, photosynthetic cyanobacteria with low nutrient requirements and versatile metabolism, could offer a sustainable platform for the heterologous production of organic compounds directly from sunlight and CO2. This strategy has been applied for the photoautotrophic production of sucrose by a genetically engineered cyanobacterium, Synechocystis sp. PCC 6803 strain S02. As the key concept in the current work, this can be further used to generate organic carbon compounds for different heterotrophic applications, including for the whole-cell biotransformation by yeast and bacteria. Results Entrapment of Synechocystis S02 cells in Ca2+-cross-linked alginate hydrogel beads improves the specific sucrose productivity by 86% compared to suspension cultures during 7 days of cultivation under salt stress. The process was further prolonged by periodically changing the medium in the vials for up to 17 days of efficient production, giving the final sucrose yield slightly above 3000 mg l−1. We successfully demonstrated that the medium enriched with photosynthetically produced sucrose by immobilized Synechocystis S02 cells supports the biotransformation of cyclohexanone to ε-caprolactone by the E. coli WΔcscR Inv:Parvi strain engineered to (i) utilize low concentrations of sucrose and (ii) perform biotransformation of cyclohexanone to ε-caprolactone. Conclusion We conclude that cell entrapment in Ca2+-alginate beads is an effective method to prolong sucrose production by the engineered cyanobacteria, while allowing efficient separation of the cells from the medium. This advantage opens up novel possibilities to create advanced autotroph–heterotroph coupled cultivation systems for solar-driven production of chemicals via biotransformation, as demonstrated in this work by utilizing the photosynthetically produced sucrose to drive the conversion of cyclohexanone to ε-caprolactone by engineered E. coli.

Cyanobacteria as cell factories for the photosynthetic production of sucrose

“…The biosynthetic pathway for p-coumaric acid was introduced into V. natriegens and co-cultures of these engineered strains with S. elongatus PCC 7942 allowed for photosynthetically driven p-coumaric acid production (Li C. et al, 2022). Other recent reports provide further evidence of the flexibility of this cyanobacterial co-cultivation system (see Table 2), including bioproduction of fatty acids (Li C. et al, 2022), ε-caprolactone (Toth et al, 2022), lactate (Li C. et al, 2022), and secreted enzymes (Hays et al, 2017). Additionally, some products can be used to feed downstream bacteria and develop more complex systems.…”

Bioinspired mechanically stable all-polysaccharide based scaffold for photosynthetic production

“…The methodology to prepare self-standing TCNF hydrogel films with MLG and Ca 2+ (hereby MLG-Ca 2+ -TCNF) was modified from Rissanen et al 22 It should be noted that the utilised Ca 2+ cross-linking procedure is a standard method to cross-link cell immobilisation matrices. 21,50 The CaCl 2 crosslinking is featured also in the TCNF-based immobilisation matrices where dual cross-linking based on polyvinyl alcohol and CaCl 2 has been investigated. 22,51 1 wt% TCNF was mixed with either 0.01 wt%, 0.02 wt%, 0.05 wt%, 0.1 wt%, or 0.2 wt% LVMLG, MVMLG, or HVMLG.…”

Rewiring photosynthetic electron transport chains for solar energy conversion

“…Biotransformations in microbial consortia have also been achieved by exploiting syntrophy. Cyanobacterial sucrose synthesis has been used to drive biotransformations in E. coli 171 , whilst a three-species co-culture of a cyanobacterium producing carbohydrates and a purple bacterium producing ammonia has been used to drive antibiotic synthesis by a heterotroph 109 . Cyanogenic glucoside synthesis has been performed in ex vivo R-PETCs using plant thylakoids and ferredoxin-cytochrome P450 fusions 23 .…”