Expression of romA and letA in Legionella pneumophila during different phases of life cycle and in different Acanthamoeba hosts

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Expression of romA and letA in Legionella pneumophila during different phases of life cycle and in different Acanthamoeba hosts

 

Author: Young, Chi Pong
Title: Expression of romA and letA in Legionella pneumophila during different phases of life cycle and in different Acanthamoeba hosts
Degree: M.Sc.
Year: 2015
Subject: Legionella pneumophila.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Health Technology and Informatics
Pages: xiii, 87 leaves : illustrations (some color) ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2780684
URI: http://theses.lib.polyu.edu.hk/handle/200/7878
Abstract: Introduction: Legionella is a Gram negative bacterium which is mainly found in water sources. The organism is transmitted through inhalation of contaminated water aerosols, which allows the bacteria to infect the alveolar macrophages to cause Legionnaires' disease. Outbreaks were reported worldwide. Legionella does not only infect human macrophages but also Acanthamoeba. Legionella's life cycle is biphasic which is composed of transmission and replicative phases. Many genes are involved in controlling the characteristics of each phase and the regulatory gene, letA, plays an important role in the regulation process. Recently, a novel gene romA was identified. romA encodes a protein that is able to trimethylate the histone H3 at K14 and causes adverse effects on host cells. However, up to the moment, the information about romA is very limited. Aims: This study aimed to determine whether Legionella has different levels of romA expression during different phases of life cycle and in different Acanthamoeba hosts. This study also determined whether expression of romA correlates with that of a global gene regulator, letA. Methods: Two sets of Legionella pneumophila (L. pneumophila) samples were prepared. One set of L. pneumophila was cultured on buffered charcoal yeast extract agar (i.e. nutrient-rich) and phosphate buffer saline (i.e. nutrient-poor) to induce the bacteria to enter replicative and transmission phase respectively. Another set of L. pneumophila was co-cultured with Acanthamoeba polyphaga (A. polyphaga) and Acanthamoeba castellanii (A. castellanii). Real-time polymerase chain reaction was performed to study the expressions of romA and letA. Results: For the L. pneumophila cultured in different nutrient conditions, there were significant differences in the expressions of letA (p<0.05) and romA (p<0.05) and the expressions for both genes were stronger in nutrient-poor condition. Moreover, the correlation coefficient of letA and romA expresssion was +0.952 which showed strong positive correlation. For the L. pneumophila co-cultured with different species of Acanthamoeba, there was no significant difference of romA expression (p>0.05) of intracellular L. pneumophila inside A. polyphaga and A. castellanii. Conclusion: romA expression of L. pneumophila was significantly stronger during transmission phase and its expression was strongly positive correlated with letA expression. Moreover, there was no significant difference of romA expression of L. pneumophila inside A. polyphaga and A. castellanii.

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