טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentLinetsky Alexander
SubjectThe genetic origin of biotype 3 in Vibrio vulnificus
DepartmentDepartment of Biotechnology and Food Engineering
Supervisor Professor Yechezkel Kashi
Full Thesis textFull thesis text - English Version


Abstract

Vibrio vulnificus is an opportunistic human pathogen identified during the 1970s. Its habitat is marine and estuarine environments throughout the world. V. vulnificus is the main cause of death due to consumption of contaminated seafood in the United States. Infections by this pathogen are contracted mainly by consumption of contaminated seafood, or by infection via a skin wound.

  There are currently three identified biotypes of V. vulnificus. Biotype 1 is the most common biotype, found worldwide, it is responsible for the most of the clinical cases involving seafood. Biotype 2, identified in the 1980s, is mainly a pathogen of eels and a secondary pathogen to humans. Biotype 3 is the most recently identified biotype. Geographically confined to Israel, it is responsible for the majority of the clinical cases there. It is usually associated with fish, and contracted mostly via skin wounds due to fish handling. The emergence of this new virulent biotype was hypothesized to be due to a genome hybridization event between two different biotype 1 populations.

   Our group has made use of the newly available microarray technology, in the form of the GoldenGate assay by Illumina, to conduct a large genotyping study of a panel of 254 V. vulnificus isolates. The isolates were obtained through various sources as well as sampling by our group, and covered geographic origins from all over the world, all three biotypes and clinical and environmental isolates. The microarray was custom designed to cover the entire V. vulnificus genome with 570 SNP loci.

  The results from the V. vulnificus genotyping were used in this study, with the goal of finding insight into the evolution of the newly emerged biotype 3 in Israel. The main steps of the research were: the creation of the dataset for the study by isolating the relevant data from the genotyping results, transforming the data with various methods to make it reflect the relation between biotype 3 and the suspected biotype 1 origin, analyzing the obtained transformations to find statistically significant groupings of the selected isolates, and finally creating an origin map for the genotyped SNPs which cover the span of biotype 3 genome.

  The origin map has allowed us to come to a conclusion that a sub-group of biotype 1 we called clade B, which is comprised of various, clinical and environmental, isolates of biotype 1 from Israel, probably shares a common ancestor with the newly emerged biotype 3. The distribution of the various origins on the map, suggests that the core genome likely belonging to clade B has undergone multiple lateral gene insertion events over time, as opposed to a single hybridization event. This has brought us to the hypothesis that V. vulnificus has a highly active gene acquisition mechanism which allows it to acquire genes from the environment, thus providing it with an evolutionary advantage. We hypothesis that in the Israeli fish farms 'melting pot' the acquisition of genes by biotype 1 isolates had eventually led to a change in biotype, and the creation of biotype 3.