Bioconversion Of Lignocellulosic 'Waste' To High-Value Food Proteins: Recombinant Production Of Bovine And Human Alpha(S1)-Casein Based On Wheat Straw Lignocellulose

Lignocellulosic biomass is the most abundant bio-resource on earth, mainly composed of D-glucose, D-xylose and L-arabinose. It is widely considered to be a promising alternative feedstock for biotechnological processes. Here we evaluated its potential to be the carbon source for growth of broadly distributed and well-established Escherichia coli laboratory and protein expression strains as well as a classic probiotic E. coli strain. E. coli DH5 alpha, E. coli K12-MG1655, E. coli K12-W3110, E. coli BL21(DE3) and E. coli Nissle 1917 were cultivated in mineral media containing single lignocellulosic sugar components. Sugar consumption in these cultures and growth parameters of the different strains were characterized. enhanced green fluorescent protein (eGFP) was chosen as a first easy to measure and prominent model recombinant target protein to demonstrate lignocellulose-dependent recombinant protein production in E. coli. To open new production routes for high value food proteins based on lignocellulose, structural genes encoding bovine alpha(S1)-casein and human alpha(S1)-casein were synthesized, cloned and then expressed in an E. coli T7 expression system in different media based on single sugars and a synthetic wheat straw mixture. Successful recombinant production of both bovine and human alpha(S1)-caseins in E. coli under these experimental conditions was demonstrated and quantified by densitometric analysis after protein separation in polyacrylamide gels. Finally, efficient casein production in E. coli based on a real hydrolysate obtained by steam explosion of wheat straw lignocellulose in a bioreactor-based batch production process was successfully demonstrated. We believe that this proof-of-concept presented here is a promising starting point to open new routes for the production of food or feed proteins with high nutritional and economic value. As such, a valorization of bulk residual biomass like lignocellulose is envisioned as a key support of a growing and truly sustainable bioeconomy.