Evolution of bacterial diversity during two-phase olive mill waste (“alperujo”) composting by 16S rRNA gene pyrosequencing

[Display omitted] •Actinobacteria, Bacteriodetes, Firmicutes and Proteobacteria were the main phyla detected.•Mesophilic and thermophilic phases did not affect bacterial population.•Maturation increased bacterial diversity, especially due to new bacterial population were detected.•Planomicrobium and Ohtaekwangia are proposed as biomarkers of AL composting maturation. Microorganisms are the main contributing factor responsible for organic matter degradation during composting. In this research, the 454-pyrosequencing of the 16S rRNA gene was used to elucidate evolution of bacterial diversity during mesophilic, thermophilic and maturation composting stages of the two-phase olive mill waste (“alperujo”), the main by-product of the Spanish olive oil industry. Two similar piles were performance composting AL with sheep manure as bulking agent. Actinobacteria, Bacteriodetes, Firmicutes and Proteobacteria were the main phyla found in genomic libraries from each composting phase. Shannon and Chao1 biodiversity indices showed a clear difference between the mesophilic/thermophilic and maturation phases, which was mainly due to detection of new genera. PCA analysis of the relative number of sequences confirmed maturation affected bacterial population structure, and Pearson correlation coefficients between physicochemical composting parameters and relative number of genera sequences suggest that Planomicrobium and Ohtaekwangia could be considered as biomarkers for AL composting maturation.