Recombinant surface display of lichenase on Bacillus subtilis spores to improve animal feed digestibility

Abstract

Bacillus subtilis is a well-characterised sporulating organism that has been extensively used as a probiotic in animal feed. The last few decades have seen increasing usage of feed enzymes to improve the nutrient availability of feed substrates. Lichenases are beta-1,3-1,4-glucanases that hydrolyse mixed beta-glucans, a major component of feed non-starch polysaccharides (NSP). Spores of Bacillus subtilis have been engineered to display proteins of interest on their surface. In this study, an industrially relevant lichenase, BglS was displayed on Bacillus subtilis spores via genetic fusion with native spore coat proteins, CotB, CotC and CotG. Among the spore-surface-displayed (SSD) constructs, CotB-BglS showed the greatest thermal stability compared to the free enzyme (~30% activity remaining after 4 hours at 50 degrees C) and retained activity after exposure to pepsin and trypsin. Moreover, CotB-BglS outperformed the free enzyme on feed substrates, achieving an 87.5% higher yield of reducing sugars from oat bran and a 150% higher yield from wheat bran. To the best of our knowledge, this is the first report of recombinant spore surface display of a lichenase. Thus, recombinant Bacillus subtilis spores displaying BglS can hydrolyse feed substrates and may be developed to combine feed-enzyme delivery with probiotic activity.