Comparative metatranscriptomic analysis of anaerobic digesters treating anionic surfactant contaminated wastewater

A metatranscriptomic approach was applied to reveal active biological functions and their assigned taxonomic profiles in complex microbial communities of anaerobic reactors applied to anionic surfactant degradation. For this purpose, three laboratory scale upflow anaerobic sludge blanket (UASB) reactors under different feeding types were compared. The feedings were synthetic medium (UASB_Control), synthetic medium and linear alkylbenzene sulfonate (LAS; UASB_SL), and real laundry wastewater (UASB_LW). A homemade bioinformatics pipeline combined to an R workflow was developed to perform trimming, co-assembling, gene calling, mapping, assignment and statistical analyses of metatranscriptomic datasets. UASB_SL and UASB_LW showed similar percentages of LAS removal (~50 %). UASB_SL showed the greatest richness and metabolic activity, followed by UASB_LW and UASB_Control. Rarefaction analysis using KO numbers revealed that 1-2 million reads were sufficient to access the functional capacity of the studied microbiomes. Genes and taxonomies associated in all steps of anaerobic LAS biodegradation were observed with high relative abundance in the UASB_SL and UASB_LW than UASB_Control. Therefore, our data corroborates the fumarate addition as the activation mechanism to initiate the removal of LAS by fumarate reductase enzyme assigned to the Syntrophobacter genus. The beta-oxidation step could be performed by Smithella, Acinetobacter and Syntrophorhabdus, whereas, for the ring cleavage a 6-OCH-CoA hydrolase attributed to the genus Desulfomonile and Syntrophorhabdus were found. In the last step, desulfonation, were observed the active genera Desulfovibrio and Desulfomonile. Thus, the integration of physicochemical results from the biological reactors and the taxonomy and functional annotations of mRNA provides a powerful tool to understand the microbial consortium involved in the biodegradation of LAS.