Microorganisms are the main responsible for the organic matter degradation during composting. In this research, 454-pyrosequencing approach has been used to elucidate how bacterial diversity and evolution were affected during two-phase olive mill waste (“alperujo”), the main by-product of the Spanish olive oil industry. The main phyla found during the process were Actinobacteria, Bacteriodetes, Firmicutes and Proteobacteria. In general, mesophilic and thermophilic phases did not affected bacterial population, only maturation by increasing their diversity, especially due to new bacterial population were detected. The most abundant genera in mesophilic/thermophilic phases were Bordetella, Flavobacterium, Halomonas, Halotalea, Olivibacter, Parapedobacter, Planifilum, Pseudomonas, Pseudoxanthomonas, Sphingobacterium; whereas Planomicrobium, Flavobacterium, Chryseobacterium, Pseudomonas, Ohtaekwangia, Sphingobacterium, Pedobacter and Luteimonas were the predominant genera during maturation, respectively. According to Pearson correlation between the main composting parameters and genera sequences, Planomicrobium and Ohtaekwangia could be a biomarkers of AL composting maturation.
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