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

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

JOURNAL=Frontiers in Chemistry

VOLUME=11

YEAR=2023

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2023.1158147

DOI=10.3389/fchem.2023.1158147

ISSN=2296-2646

ABSTRACT=<p>Poly-γ-glutamic acid (γ-PGA) is a bio-derived water-soluble, edible, hydrating, non-immunogenic polymer. <italic>Bacillus subtilis</italic> 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 <italic>Laminaria digitata, Saccharina latissima</italic> and <italic>Alaria esculenta-</italic>were pre-treated by means of mechanical methods, sterilised and subsequently inoculated with <italic>B. subtilis</italic> natto. High shear mixing was found to be the most suitable pre-treatment technique. Supplemented <italic>L. digitata</italic> (9.1 g/L), <italic>S. latissima</italic> (10.2 g/L), <italic>A. esculenta</italic> (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 <italic>L. digitata</italic> (Avg. 4.76 g/L) comparable to those obtained with GS media (7.0 g/L). Further, pre-treated <italic>S. latissima</italic> and <italic>L. digitata</italic> 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.</p>