Effect of Flagellar Mutations on Yersinia enterocolitica Biofilm Formation

Abstract

Yersinia enterocolitica biovar 1B is one of a number of strains pathogenic to humans in the genus Yersinia. It has three different type III secretion systems, Ysc, Ysa, and the flagella. In this study, the effect of flagella on biofilm formation was evaluated. In a panel of 31 mutant Y. enterocolitica strains, we observed that mutations that abolish the structure or rotation of the flagella greatly reduce biofilm formation when the bacteria are grown under static conditions. These results were further evaluated by assessing biofilm formation under continuous culture using a flow cell chamber. The results confirmed the important contribution of flagella to the initiation of biofilm production but indicated that there are differences in the progression of biofilm development between static growth and flow conditions. Our results suggest that flagella play a critical role in biofilm formation in Y. enterocolitica.Yersinia enterocolitica is a food-borne, pathogenic, gramnegative bacterium that causes gastroenteritis. In some cases, septicemia can occur, depending on the health of the host. The most serious illnesses are developed by young children under the age of 1 year (1). Y. enterocolitica is one of three humanpathogenic species in the genus Yersinia that, along with Yersinia pseudotuberculosis, causes gastroenteritis. The third species, Yersinia pestis, is the causative agent of plague. Historically, the formation of biofilms by Y. pestis has been better studied than biofilms of the other two. It has been suggested that Y. pestis biofilms induce starvation of fleas by blocking their digestive tracts. These biofilms seem to affect the fleas but play no role in mammalian pathogenesis, as Y. pestis strains unable to form biofilms are still able to be transmitted by fleas and cause disease (23-25, 53).There are many studies showing the importance of flagella in biofilm formation in other bacteria (32,61,67). In Escherichia coli, a screen showed that 34 of 72 adhesion-deficient strains had changes in motility characteristics (31). Another screen showed that about half the strains that were biofilm defective also exhibited changes in motility function (67), and while motility was a critical factor under certain biofilm formation conditions, chemotaxis was not required (67). Flagella are involved in the adherence of enteropathogenic E. coli to epithelial cells (32), and flagella are also important for biofilm development in Pseudomonas aeruginosa and Aeromonas spp. (61). However, there are other studies that suggest that flagella are not essential for biofilm formation in E. coli (68), P. aeruginosa (47), and Pseudomonas fluorescens (74). These studies suggest that the critical contribution of flagella to biofilm formation is conditional.Among the three pathogenic Yersinia strains, only Y. enterocolitica and Y. pseudotuberculosis are motile. Y. pestis has a frameshift in flhD, the flagellar-biosynthesis regulator protein, and is therefore nonmotile. The goal of this study was to determine whether flagella and motility...

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