Untangling the Effect of Fatty Acid Addition at Species Level Revealed Different Transcriptional Responses of the Biogas Microbial Community Members

In
the present study, RNA-sequencing was used to elucidate the change
of anaerobic digestion metatranscriptome after long chain fatty acids
(oleate) exposure. To explore the general transcriptional behavior
of the microbiome, the analysis was first performed on shotgun reads
without considering a reference metagenome. As a second step, RNA
reads were aligned on the genes encoded by the microbial community,
revealing the expression of more than 51 000 different transcripts.
The present study is the first research which was able to dissect
the transcriptional behavior at a single species level by considering
the 106 microbial genomes previously identified. The exploration of
the metabolic pathways confirmed the importance of Syntrophomonas species in fatty acids degradation, and also highlighted the presence
of protective mechanisms toward the long chain fatty acid effects
in bacteria belonging to Clostridiales, Rykenellaceae, and in species of the genera Halothermothrix and Anaerobaculum. Additionally, an interesting transcriptional
activation of the chemotaxis genes was evidenced in seven species
belonging to Clostridia, Halothermothrix, and Tepidanaerobacter. Surprisingly, methanogens
revealed a very versatile behavior different from each other, even
among similar species of the Methanoculleus genus,
while a strong increase of the expression level in Methanosarcina sp. was evidenced after oleate addition.