Tannic acid degradation by bacterial strains Serratia spp. and Pantoea sp. isolated from olive mill waste mixtures.

A mixture made of Olive Mill Waste (OMW) and hygroscopic organic additives was stored in indoor and outdoor stack piles. A significant decrease in organic matter and polyphenols was detected in indoor stack pile (51.5% and 75% of initial contents, respectively). Three bacterial strains isolated from OMW indoor stack pile were able to grow in the presence of tannic acid as sole carbon and energy source, and were named 2AT1, 2AT2, and 2AT3. 16S rRNA gene sequencing assigned isolates 2AT1 and 2AT3 to the genus Serratia, and strain 2AT2 to the genus Pantoea. The highest tannase activity was pointed out in the Pantoea sp. strain 2AT2, and growth tests showed a maximum degradation rates of tannic acid within 6 h and a complete depletion in 24 h for all isolates. Glucose and gallic acid were detected in the bacterial cultures as breakdown products of tannic acid added to the mineral culture-medium as the sole carbon and energy source. This was the first evidence of bacterial strains able to degrade tannic acid isolated from OMW.