Abstract
SummaryHigh‐strength polymers, such as aramid fibres, are important materials in space technology. To obtain these materials in remote locations, such as Mars, biological production is of interest. The aromatic polymer precursor para‐aminobenzoic acid (pABA) can be derived from the shikimate pathway through metabolic engineering of Bacillus subtilis, an organism suited for space synthetic biology. Our engineering strategy included repair of the defective indole‐3‐glycerol phosphate synthase (trpC), knockout of one chorismate mutase isozyme (aroH) and overexpression of the aminodeoxychorismate synthase (pabAB) and aminodeoxychorismate lyase (pabC) from the bacteria Corynebacterium callunae and Xenorhabdus bovienii respectively. Further, a fusion‐protein enzyme (pabABC) was created for channelling of the carbon flux. Using adaptive evolution, mutants of the production strain, able to metabolize xylose, were created, to explore and compare pABA production capacity from different carbon sources. Rather than the efficiency of the substrate or performance of the biochemical pathway, the product toxicity, which was strongly dependent on the pH, appeared to be the overall limiting factor. The highest titre achieved in shake flasks was 3.22 g l−1 with a carbon yield of 12.4% [C‐mol/C‐mol] from an amino sugar. This promises suitability of the system for in situ resource utilization (ISRU) in space biotechnology, where feedstocks that can be derived from cyanobacterial cell lysate play a role.
Highlights
Introduction and backgroundSummaryHigh-strength polymers, such as aramid fibres, are important materials in space technology
The present study provides a holistic picture of how a biological platform technology supporting in situ resource utilization (ISRU) for production of para-aminobenzoic acid (pABA) may be established
Production was demonstrated from various carbon sources, at the highest resulting in a titre of 3.22 g lÀ1 with a yield of 12.4% [C-mol C-molÀ1] despite the observed high toxicity of pABA
Summary
Plastics and polymers are omnipresent in our everyday life but are potentially of even greater importance in space technology. In Escherichia coli, a concentration of 4.8 g lÀ1 (35 mM) was reached from glucose (Koma et al, 2014), while the highest production to date was accomplished with Corynebacterium glutamicum, reaching 43.06 g lÀ1 (314 mM) from glucose (Kubota et al, 2016) To leverage this technology in space and enable the synthesis of aramid fibres, it would be highly desirable to produce pABA in Bacillus subtilis, the organism most suited to space synthetic biology. Bacillus subtilis forms endospores (Nicholson et al, 2000; Horneck et al, 2010), which are extremely resistant to several environmental parameters such as drought, salinity, pH and solvents and remain viable for decades; as long as protected from UV radiation, they even endure the vacuum of space (Horneck, 1993) This allows for convenient long-term storage of a microbial cell factory while in transit and revitalization for ISRU at destination. The present study provides a holistic picture of how a biological platform technology supporting ISRU for production of pABA may be established
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