Morphology, Virulence and Epidemiology of Bacteriophage Particles Isolated from Industrial Vinegar Fermentations

Abstract

Summary Bacteriophage particles could be demonstrated in disturbed industrial vinegar fermentations both in submerged and trickling generators. A total of 300 samples from disturbed vinegar fermentations collected in Germany, Danmark and Austria, were examined by electron microscopy. 70% of the samples from submerged generators contained phage particles at numbers of at least 10 7 –10 9 /ml in the crude reactor content, whereas phage particles were always present in trickling generators at numbers of 10 6 –10 7 /ml. The phage particles were isometric-headed with long contractile tails, belonging to the group A of Bradley . 7 morphologically different types were identified based on head sizes, tail lengths and diameters. Head sizes varied between 60 and 110 nm. The corresponding tail lengths ranged from 99 to 360 nm with tail diameters from 14 to 31 nm. To prove infectivity of the observed phage particles for Acetobacter europaeus , the main species in industrial fermenters, a spirit vinegar culture in a laboratory submerged fermenter was infected with the bacteriophage fraction isolated by centrifugation from a trickling generator. The culture was lysed within a few hours, releasing high numbes of a specific bacteriophage as estimated by direct electron microscopy. This phage induced fermentation breakdown lasted for nearly 2 weeks. 18 days after fermentation stop, a new Acetobacter europaeus strain grew up in the fermenter characterized by a plasmid profile different from the strain present at the moment of phage addition. This experiment showed that the traditional trickling generator filled with beechwood chips is a potent source of virulent bacteriophages for cultures used in submerged fermenters. A. europaeus is not able to grow in soft agar preventing the use of the classical plaque test to enumerate infective bacteriophages.