Microbial diversity during hemp field retting.

Hemp field retting is a bioprocess used to facilitate the mechanical extraction of fibres from hemp stem by dissolving amorphous components surrounding the fibre bundles. This dissociation is due to the production of specific enzymes by microorganisms (bacteria and fungi) that colonize the surface of the stems during the retting process. Retting is carried out empirically by the farmers.A better knowledge of the main actors of the retting process, which are the microbial communities, is required for better management of this process. Thus, this study aims to investigate the temporal dynamics of the bacterial and fungal communities involved in the retting process. To this end, we applied a high-throughput sequencing approach (HTS) on hemp stems and soil samples obtained over 6 weeks of retting. The results show eleven bacterial and seven fungal phyla in soil samples and seven bacterial and two fungal phyla in hemp stem samples. New phyla are discovered in this study not previously associated with hemp field retting. Bacterial dominant phyla were Proteobacteria, Actinobacteriota, Myxococcota, Bacteroidota, Acidobacteriota, and Firmicutes. Fungal dominant phyla were Ascomycota, Basidiomycota, Mucoromycota, and Chytridiomycota. In addition, enzymatic activity measurements were carried out simultaneously on hemp stems. This study provides the first thorough description of the biological mechanisms of hemp field retting, revealing the important evolution of microbial groups involved in this process. These findings could lead to the discovery of simple indicators to better control field retting and obtain high-value fibres, ultimately improving the consistency of fibre quality.