A Phenotype at Last: Essential Role for the Yersinia enterocolitica Ysa Type III Secretion System in a Drosophila melanogaster S2 Cell Model

Abstract

The highly pathogenic Yersinia enterocolitica strains have a chromosomally encoded type III secretion system (T3SS) that is expressed and functional in vitro only when the bacteria are cultured at 26°C. Mutations that render this system nonfunctional are slightly attenuated in the mouse model of infection only following an oral inoculation and only at early time points postinfection. The discrepancy between the temperature required for the Ysa gene expression and the physiological temperature required for mammalian model systems has made defining the role of this T3SS challenging. Therefore, we explored the use of Drosophila S2 cells as a model system for studying Ysa function. We show here that Y. enterocolitica is capable of infecting S2 cells and replicating intracellularly to high levels, an unusual feature of this pathogen. Importantly, we show that the Ysa T3SS is required for robust intracellular replication. A secretion-deficient mutant lacking the secretin gene, ysaC, is defective in replication within S2 cells, marking the first demonstration of a pronounced Ysa-dependent virulence phenotype. Establishment of S2 cells as a model for Y. enterocolitica infection provides a versatile tool to elucidate the role of the Ysa T3SS in the life cycle of this gastrointestinal pathogen.

Yersinia enterocolitica Inhibits Salmonella enterica Serovar Typhimurium and Listeria monocytogenes Cellular Uptake

“…Recently, it was demonstrated that enteropathogenic Escherichia coli (EPEC) inhibits H. pylori-induced activation of Rho GTPase Rac1 via Tir-intimin interaction (70). Our data clearly show that inhibition of Salmonella uptake in HeLa cells requires Y. enterocolitica Ysa T3SS at 37°C, but another recent study conducted by Walker et al (26) has identified an invasion phenotype for Ysa using S2 insect cells at 26°C. Thus, our results suggest an additional role played by Ysa at 37°C (Fig.…”

“…1B is also a food-borne pathogen and, like S. Typhimurium, translocates numerous T3SS effector proteins, called Yops, into the host cell cytosol using both the Ysc T3SS encoded on the virulence plasmid, pYV, and the Ysa T3SS encoded on the chromosome (25)(26)(27)(28)(29). However, in contrast to S.…”

Transcriptomic Analysis of Yersinia enterocolitica Biovar 1B Infecting Murine Macrophages Reveals New Mechanisms of Extracellular and Intracellular Survival

“…Initial studies found the Ysa T3SS to be expressed in vitro only at 26°C in nutrient-rich media containing Ͼ150 mmol/liter salt (NaCl or KCl) (69), conditions that would not suggest a role in the infection of a mammalian host. Because of this phenotype of low-temperature induction, Walker et al examined the expression of the system during the infection of Drosophila S2 cells and found that it was required for growth only when internalized (70).…”

Regulation of bacterial virulence gene expression by cell envelope stress responses

“…In this case RcsB positively regulates expression of the Ysa T3SS-encoding genes, which are found in highly pathogenic biogroup B1 strains and might be important in mammals or insects. [126][127][128] RcsB is involved in activating expression of the ysaE operon, which encodes a master regulator of the ysa locus and structural components of the T3SS. However, the mechanism by which this occurs is unclear and it is not yet known if RcsB binds to the ysaE promoter.…”