Microbial population dynamics and meta-proteomic evaluation for functional insight into an anaerobic membrane bioreactor during startup

Abstract

Startup of an anaerobic membrane reactor (AnMBR) involves a significant concentration of active and functioning microbial communities participating in the process. Here, we monitored the physical, microbial, and functional performance during the first 90 days of AnMBR operation. The results indicate initiation of anaerobic digestion on days 31–60 (transitional stage) and its stabilization on days 61–90 (stable stage), with an average COD removal efficiency of 93.14 ± 1.41% and biogas production of 0.82 ± 0.15 L/d. Moreover, the microbial population and its associated proteome were studied using 16s rDNA-based PCR-DGGE and SDS-PAGE-LC/MS/MS techniques to acquire a detailed understanding of reactor startup conditions. Later, a conventional library was created through the UniprotKB protein database using the observed community of all organisms identified with 16s rDNA sequencing. The results clearly depicted Gammaproteobacteria as the dominant fermentative during the initial and transitional stages. Firmicutes predominated over Gammaproteobacteria during the stabilization stage. During the transitional stage, methanobacteriales and metheanosarcinales coexisted. In the two-step reaction, a combination of syntrophic acetate oxidation and hydrogenotrophic methanogenesis was observed. During the stabilization stage, diverse metheanosarcinales were detected. The methanogenic pathway seemed to shift to acetoclastic methanogenesis, as indicated by detection of acetyl-coenzyme A synthetase, aminomethyltransferase, and methyl-coenzyme M reductase. Thus, by linking microbial community dynamics with the meta-proteomic functions of AnMBR during startup, a stable reactor performance with up-regulated acetoclastic methanogenesis was observed in 90 days.