Team:HZAU-China/Project/Flea and Yersinia pestis

• Overview
• The innovation of HZAU-iGEM Team
• The design of experiment
• Rabies
• Flea and Yersinia pestis
• Bacterial Spores as Vaccine Vehicles
• Bacillus subtilis as Probiotics
• Antimicrobial Peptides
• Methods for rearing flea

The first step for safe moving vaccine factory is to transfer the bacteria into mammalian host. The HZAU-2013iGEM project idea comes from Yersinia pestis and fleas. So a good understanding of the relationship between Yersinia pestis and fleas is important.

The plague is an infectious bacterial disease which has high mortality without treatment. Because of specific clinical symptoms of pulmonary plague it became known as the Black Death. The huge breakout of it since the 6th century caused millions of deaths. The gram-negative coccobacillus now called Yersinia pestis has been found as the causative agent of plague in Hong Kong outbreak in the year of 1894. In the next few years the details of transmission of plague through rats and fleas has been discovered and experimentally verified.

Blocked fleas can transfer Yersinia pestis to mammalian host and the mechanism has been widely researched. Yersinia pestis can build biofilm http://en.wikipedia.org/wiki/Biofilms in the proventricular, which will separate the oesophagus from midgut or stomach, resulting in blockage of fleas. Blocked fleas try to feed repeatedly, causing Yersinia pestis to be regurgitated into blood and thus successfully transferring the bacteria to mammalian host. It has been considered that blockage of flea is the most common mechanism of flea-borne transmission. And Yersinia pestis starts to form a biofilm in the proventriculus when the bacteremic bloodmeal contains more than 108 cfu/ml. The flea will die after failed feeding attempts.

Yersinia pestis biofilm in the flea. Digestive tract dissected from an X. cheopis flea blocked with a dense biofilm consisting of dark masses of Yersinia pestis embedded in a paler, viscous ECM (arrows). The contiguous biofilm fills the proventriculus (PV) and extends posteriorly into the lumen of the midgut (MG). E, esophagus

This picture comes from B.J. Hinnebusch et al 2008 Curr Top Microbiol Immunol.

The biofilm model of proventricular infection was first established by Bacot. Yersinia pestis will synthesize extracellular biofilm matrix (ECM) when growing in the proventricular. It has been found that the ECM is essential for the attachment and development of a biofilm on the surface of the proventriculaar spines. The molecular level of Yersinia biofilm ECM synthesis is dependents on a four-gene operon called hmsHFRS. Hms-dependent ECM of Yersinia is structurally related to the Pga- and Ica-dependent ECMs of E.coli and staphylococcal biofilms. Except for the regulation of Hms-dependent biofilm formation, other factors such as bacterial factors and environmental factors also impact the biofilm formation. The mechanics of the biofilm formation of Y.pestis is multifactorial. Many questions are still unknown.

In order to make things easy, we choose bacillus subtilis just because it can form biofilm naturally or by genetic modification in the first stages of our project.

Reference

1. Hinnebusch, B.J, Erickson D.L. Yersinia pestis Biofilm in the Flea Vector and Its Role in the Transmission of Plague. Curr Top Microbiol Immunol, 2008;322, 229-248.

2. Hinnebusch, B. J., Perry, R. D. & Schwan, T. G. (1996). Role of the Yersinia pestis hemin storage (hms) locus in the transmission of plague by fleas. Science 273, 367–370.

3. Jarrett, C. O., Deak, E., Isherwood, K. E., Oyston, P. C., Fischer, E. R.,Whitney, A. R., Kobayashi, S. D., DeLeo, F. R. & Hinnebusch, B. J.(2004). Transmission of Yersinia pestis from an infectious biofilm in the flea vector. J Infect Dis 190, 783–792.