Abstract

IntroductionEnergy crisis and environmental pollution have led to an increasing interest in renewable energies. Biogas production from plant material, agricultural residual products and food wastes represents one of the most economically attractive alternative technology for biofuel production. In this regards, anaerobic digestion has been widely applied to produce methane for biofuel. Complex consortia of microorganisms are responsible for biomass degradation and biogas production involving several stages such as substrate hydrolysis, acidogenesis, acetogenesis and methanogenesis. In this sense, the next-generation high-throughput sequencing provides a powerful tool for dissecting microbial community structure and methane-producing pathways in anaerobic digestion. Here, a taxonomic and functional metagenomic analysis of microbial community residing in an industrial-scale biogas fermenter has been carried out at different steps of biogas production.MethodsSample were collected from an industrial-scale mesophilic plant, daily fed with maize silage, consisting of a three steps production taking place in a bioreactor, post-reactor and a storage tank. Total DNA was extracted from samples belonging to each stage of biogas production. Metagenomic analysis were carried out by 16S and shotgun sequencing approach. The 16S datasets were generated by sequencing the bacterial and archaeal V4 hypervariable region. Reads from 16S sequencing were aligned against SILVA ribosomal RNA sequence database by using MALT (1), while shotgun reads were aligned against NCBI-nr sequence database by using DIAMOND (2). Taxonomic binning and functional annotation were performed with MEGAN 6 software (3). ResultsOver 14.5 million high quality reads (about 3.4 gigabases) were generated on the Ion Torrent S5 Sequencing System. About 2.4 and 3 million reads were assigned for 16S and shotgun approach, respectively. Although the average number of assigned taxa for 16S analysis was considerably lower than shotgun analysis, the overall taxa distribution resulting from both sequencing strategies was conserved. In detail, metagenomic analysis revealed that the superkingdom of Bacteria was dominant (~93%) along the production steps, whereas Archaea were less represented (~4%). Within Bacteria the most abundant phyla were Firmicutes, mostly represented by Clostridia, followed by Bacteroidetes, Synergistetes and Proteobacteria. Within the superkingdom of Archaea, only microorganisms belonging to the phylum of Euryarchaeota were detected. Within Euryarchaeota the dominant genera were Methanosarcina and Methanoculleus, notably to be key microorganisms involved in methanogenesis. Data showed that during biogas production steps the abundance of Methanosarcina genus decreased from bioreactor to storage tank, with a simultaneous increase of Methanoculleus genus. Functional analysis of assigned reads also supported a shift from acetotrophic methanogens to hydrogenotrophic methanogens.

Autore Pugliese

• Mule' Giuseppina , Fanelli Francesca , Ferrara Massimo

Tutti gli autori

• M. Ferrara; V. C. Liuzzi; F. Fanelli; D. H. Huson; G. Mulè

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Anno di pubblicazione

2017

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