Cellulolytic Bacillus Strain: Production Optimization Using Wheat Bran under Solid-State Fermentation and Investigation of Its Probiotic Potential

Abstract

Attention to the association of cellulolytic bacteria with probiotic potential as an additive in animal feeding has risen in the last decades. Such additive use in livestock feed is essential in improving animal health, growth, and production performances. This study was designed to identify probiotic characteristics and test the cellulolytic ability of Bacillus strains isolated from the dromedary gastrointestinal tract. Thus, thirty-two Bacillus strains were tested for their cellulolytic ability on cellulose Congo-red agar media. Among the isolates, only the strain D1B3 showed the largest degradation zone (2.4 cm) and was identified as Bacillus amyloliquefacians by 16S rRNA gene sequence analysis. Solid-state fermentation (SSF) retained this strain for cellulase and biomass production using wheat bran as a substrate. The fermentation was optimized through a central composite design, by exploring three factors: incubation temperature, moisture ratio, and pH. Biomass and cellulose enzyme activity were selected as responses and corresponding regression coefficients were calculated. The optimal parameters were: liquid-to-solid ratio (1.19%), pH buffer (6.2), and incubation temperature (36.99 °C) to obtain the highest level of biomass and cellulose enzyme activity reaching a value of 9.828 log CFU/g and 0.0144 g/L.min, respectively. The potentiality of Bacillus amyloliquefacians D1B3 as a probiotic was examined in vitro. It also showed antimicrobial activity against Pseudomonas aeruginosa 9027, Klebsiella pneumoniae, and Escherichia coli 10536. The isolate tolerates low pH and bile salt (0.3% Oxygall). The hydrophobicity and coaggregation abilities were 1.7% and 69.79%, respectively. The results indicated that Bacillus amyloliquefacians D1B3 could be a potential probiotic additive for improving in vitro fermentation of wheat bran and suggests the possibility of combining the probiotic attributes of this strain with its cellulolytic ability to enhance the rumen fermentation of animal feed.