Assessment of the diversity and abundance of the total and active fungal population and its correlation with humification during two-phase olive mill waste ("alperujo") composting.

• Ascomycota was the predominant phyla during "alperujo" composting. • Penicillium , Debaryomyces and Sarocladium were the main genera detected. • The abundance of total and active fungal population were increased during composting. • Some Basidiomycota were correlated with humification. • Cystofilobasidium could be a potential fungal biomarker to assess AL compost maturation. Metagenomic and transcriptomic techniques applied to composting could increase our understanding of the overall microbial ecology and could help us to optimise operational conditions which are directly related with economic interest. In this study, the fungal diversity and abundance of two-phase olive mill waste ("alperujo") composting was studied using Illumina MiSeq sequencing and quantitative PCR, respectively. The results showed an increase of the fungal diversity during the process, with Ascomycota being the predominant phylum. Penicillium was the main genera identified at the mesophilic and maturation phases, with Debaryomyces and Sarocladium at the thermophilic phase, respectively. The fungal abundance was increased during composting, which confirms their important role during thermophilic and maturation phases. Some Basidiomycota showed an increased during the process , which showed a positive correlation with the humification parameters. According to that, the genus Cystofilobasidium could be used as a potential fungal biomarker to assess alperujo compost maturation. [ABSTRACT FROM AUTHOR]