Extracellular polymer production and potential for aggregate formation by classical propionibacteria

Abstract

Nineteen Propionibacterium strains were screened for extracellular polymer (ECP) production. The best producer, P. jensenii S1, was introduced into two different media, Yeast Extract Lactate (YEL)-medium and Apricot Effluent (AE)-medium. The YEL medium samples were incubated in different mixing systems (a roller-table and a linear shaking platform) for 24 days at 35 °C. According to the volatile fatty acids and pH profiles, no real differences could be detected between the two mixing systems. Bacterial aggregates were, however, only observed in the roller-table samples. The process was repeated with AE-medium on the roller-table. Larger and more stable flocs were observed in the AE-medium samples. Scanning electron microscopy and PCR analysis confirmed the presence of propionibacteria in these flocs even after 5 months of storage at 4 °C. It was concluded that ECP-producing Propionibacterium strains could be manipulated to form bacterial flocs under certain environmental conditions, which might be enhanced in the presence of fibrous material occurring naturally in food industry effluents.