Fatty acids and dimethyl acetals as indicators of rumen bacterial profile variation in an in vitro tannin- supplemented model

Anaerobic and facultative anaerobic bacteria are resilient to environmental condition changes through the modulation of membrane plasticity, due to their capacity to change the composition of acyl and alkenyl chains of their phospholipids, including fatty aldehydes, under specific inputs. Perturbing the rumen ecosystem with high concentrations of antimicrobial substances like tannins could create environmental conditions that stimulate microbiota feedback mechanisms. This study aims to investigate whether changes in dimethyl acetal and fatty acids reflect rumen bacterial profile variations under specific in vitro conditions, using quebracho tannin (QT, 55 g/kg or 166 g/kg of dry matter) as a perturbing factor. The high concentrations of QT in feeds fermented in rumen inoculum (RL) have been characterized by a significant decrease in protein degradability ( P = 0.005), while neutral detergent fiber (NDF) degradability did not differ among treatments. The profile of specific cis and trans octadecenoic (C18:1) isomers, several branched-chain and polyunsaturated fatty acids (C18:2n-6, and C18:3n-3), and DMA (14:0, 13:0, i-14:0, and i-15:0) changed in the challenging environment. Microbiological analysis showed significant differences at various taxonomic levels. Multivariate analysis revealed correlations between bacterial genera, fatty acids, and DMA components, providing insight into bacterial interactions in ruminal fermentation. Perturbing the rumen ecosystem with QT created environmental conditions that enhanced the microbiota tolerance, showing the various changes in bacterial composition and biohydrogenation metabolic processes. Several fibrolytic bacteria, such as members of the genera Butyrivibrio , Pseudobutyrivibrio , and Lachnospira , showed high tolerance, ensuring the degradation of NDF. DMA 14:0 and DMA i-15:0 seem to play an interesting role in specific bacteria.