Effects of Aspergillus oryzae prebiotic on ruminal fermentation and prokaryotic and fungal microbiotas

Introduction Aspergillus oryzae prebiotics (AOP) have been shown to modulate rumen fermentation. However, their effect on the rumen microbiome has not been fully evaluated using up-to-date molecular techniques. Methods An experiment using an artificial rumen system (Rusitec) was conducted to assess the effects of newly developed AOP on rumen fermentation and prokaryotic and fungal microbiotas. The experiment was conducted for 19 d with a completely randomized design of three treatments and four replications per treatment. Treatments were Control basal diet only, basal diet supplemented with AOP at 6 mg (low dose; AOPl) or 10 mg/fermenter (high dose; AOPh) per day. Total gas, methane, ammonia, volatile fatty acids and microbial protein production were measured. Specific rumen bacteria and methanogens were analyzed using real-time PCR. Prokaryotic and fungal microbiotas were determined by sequencing regions of the 16S rRNA and ITS genes, respectively. Results and Discussion Supplementation of AOP at 6 and 10 mg/fermenter per day linearly increased total gas production (P < 0.01), dry matter disappearance (P < 0.05), neutral detergent fiber disappearance (P < 0.001), total volatile fatty acids (P < 0.01) and total microbial protein production (P < 0.05) with the most significant differences being observed between C and AOPh. However, starch disappearance, methane production and ratio of acetate: propionate were not affected by either AOPl or AOPh. PCR analysis revealed that AOP linearly increased (P < 0.05) the daily output of 16S rRNA gene copies of total cellulolytic bacteria (sum of Fibrobacter succinogenes , Ruminococcus albus and Ruminococcus flavefaciens ), and especially for F. succinogenes associated with feed particles, when analyzed separately. Microbiota analysis revealed that AOP did not affect diversity and abundances of either prokaryotes or fungi at the phylum level. However, AOP increased (P < 0.05) the abundance of cellulolytic bacterial and fungal genera. The addition of AOP to the rumen improved fermentation efficiency via positively altering the bacterial and fungal microbiota associated with fiber digestion.