A circular bioprocess application of algal-based substrate for Bacillus subtilis natto production of γ-PGA

Mattia Parati; Catherine Philip; Barbara Mendrek; David Townrow; Ibrahim Khalil; Fideline Tchuenbou-Magaia; Michele Stanley; Marek Kowalczuk; Grazyna Adamus; Iza Radecka

doi:10.3389/fchem.2023.1158147

A circular bioprocess application of algal-based substrate for Bacillus subtilis natto production of γ-PGA

Front Chem. 2023 Apr 20:11:1158147. doi: 10.3389/fchem.2023.1158147. eCollection 2023.

Authors

Affiliations

¹ Faculty of Science and Engineering, University of Wolverhampton, Wolverhampton, United Kingdom.
² Centre of Polymer and Carbon Materials, Polish Academy of Sciences, Zabrze, Poland.
³ Scottish Association for Marine Sciences, Oban, United Kingdom.

Abstract

Poly-γ-glutamic acid (γ-PGA) is a bio-derived water-soluble, edible, hydrating, non-immunogenic polymer. Bacillus subtilis natto is a wild-type γ-PGA producer originally isolated from Japanese fermented natto beans whose activity has been shown to be enhanced through ion-specific activation of Extrachromosomal DNA maintenance mechanisms. Being a GRAS γ-PGA producer, this microorganism has attracted great interest in its use within an industrial context. Here we successfully synthesised amorphous, crystalline and semi-crystalline γ-PGA between 11-27 g/L. In line with circular economy principles, scalable macroalgal biomass has been evaluated as substrate for γ-PGA, displaying great potential in both yields and material composition. In this study whole cell, freeze dried seaweed -namely Laminaria digitata, Saccharina latissima and Alaria esculenta-were pre-treated by means of mechanical methods, sterilised and subsequently inoculated with B. subtilis natto. High shear mixing was found to be the most suitable pre-treatment technique. Supplemented L. digitata (9.1 g/L), S. latissima (10.2 g/L), A. esculenta (13 g/L) displayed γ-PGA yields comparable to those of standard GS media (14.4 g/L). Greatest yields of pure γ-PGA were obtained during the month of June for L. digitata (Avg. 4.76 g/L) comparable to those obtained with GS media (7.0 g/L). Further, pre-treated S. latissima and L. digitata complex media enabled for high molar mass (4,500 kDa) γ-PGA biosynthesis at 8.6 and 8.7 g/L respectively. Compared to standard GS media, algal derived γ-PGA displayed significantly higher molar masses. Further studies will be necessary to further evaluate the impact of varying ash contents upon the stereochemical properties and modify the properties of algal media based γ-PGA with the aid of key nutrients; however, the material synthesised to date can directly displace a number of fossil fuel derived chemicals in drug delivery applications, cosmetics, bioremediation, wastewater treatment, flocculation and as cryoprotectants.

Keywords: GRAS; circular bioprocesses; industrial up-scaling; macroalgal biomass; ɣ-PGA.

Grants and funding

This work was partially supported the University of Wolverhampton Research Investment Fund (RIF4); ERDF Science in Industry Research Centre (SIRC 01R19P03464) project, BBSRC Algae-UK for Proof of Concept project BB/S009825/1; UCL Ref: 5749484, partially funded by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 872152, project GREEN-MAP and co-financed by the program of the Polish Minister of Science and Higher Education entitled “PMW” in the years 2020–2023; contract No 5092/H2020/2020/2 and European Union’s Horizon 2020 research and innovation programme under grant agreement No 774109 (project “Intelligent Management System for Integrated Multi-trophic Aquaculture—IMPAQT”).