טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentBatheesh Saleh
SubjectIsolation and Identification of Non Luminescent Marine
Bacteria Producing the Auto Inducer of Vibrio
Fischeri
DepartmentDepartment of Biotechnology and Food Engineering
Supervisor Professor Emeritus Shimon Ulitzur (Deceased)


Abstract

Many Gram negative bacteria produce derivatives of homoserine lactone (HSL) at late phases of growth. These molecules were found to have an important regulatory role in different cellular functions. The first example of the regulatory role of HSL was unraveled in the complex regulation of the luminescence (lux) system of the marine luminous bacteria Vibrio fischeri. It was found that HSL (named autoinducer) binds and activates the regulatory protein LuxR, which in turn initiates the transcription of the lux system genes, including the gene responsible for the synthesis of the HSL, thus creating auto-catalytic process.

This work addressed the possibility that marine non-luminous bacteria produce HSLs that might activate the luminescence system of luminous bacteria. Indeed, during the course of this work, several non-luminous marine bacteria have been isolated that were found to excrete HSLs that induce the formation of the lux system of Vibrio fischeri. These bacteria have been partially identified and the HSLs were isolated and purified on HPLC. The analysis showed that some bacteria produce more than one type of HSL. Similar to the autoinducer of luminous bacteria, the HSLs studied appeared at late stages of growth. The possible role of the new HSLs in imitating the activity of the autoinducer of Vibrio fischeri was not elucidated.

We postulate that in the open sea these regulatory molecules induce the lux system of bacteria such as Vibrio fischeri, and by thus draw fish to the particulate matter on which they reside together with the luminous bacteria. Once eaten by the fish, the bacteria reach the rich environment of the fish gut where they can grow and multiply.