Deep Sequencing Analysis of the Eha-Regulated Transcriptome of Edwardsiella tarda Following Acidification

Abstract

In response to stresses in host cells, several transcriptional regulators described in E. tarda can activate a series of interacting signaling networks [13]. Our previous study found that Eha is a transcriptional regulator of the MarR family [14]. Eha could also regulate the mRNA levels of some surface structures like the type III secretion system to affect the intracellular survival and virulence of E. tarda [15]. We found that Eha is required for the bacteria to resist oxidative stress and survive in macrophages [16]. As the type III secretion system in E. tarda disturbs the formation of the acidic environment in phagosomes [9], we hypothesized that Eha may be required for the bacteria to resist the acid stress in macrophages.Next generation sequencing technology, RNA-Sequencing (RNAseq), has been used in bacterial transcriptome analyses [17]. We performed a high-throughput RNA-seq study, which has firstly been applied in the transcriptome analyses of E. tarda, to detect and compare the differentially-expressed genes (DEGs) between the ET13 wild type bacterium and its eha mutant following exposure to acid stress. Our present study provides the gene expression profiles and sheds light on the molecular mechanism by which E. tarda survival is regulated by Eha under acid stress conditions. Key words: Eha gene; E. tarda; RNA-seq; Macrophage; Acidification IntroductionEdwardsiella tarda (E. tarda) is a facultative intracellular pathogen that causes Edwardsiellosis in freshwater and marine fish worldwide and a Salmonella-like gastroenteritis in humans [1,2]. Macrophages play critical roles in the defense against invading bacteria. Zhang et al. showed that E. tarda can utilize macrophages as a niche to initiate its virulence and spread systemic infections [3]. However, there are various stressful conditions such as nutrition deprivation, low pH and high reactive oxygen species (ROS) present in the intracellular niche of the phagocytes [4]. There are the strategies that virulent bacterial strains use to evade phagosomes and escape into the cytosol to enable their survival in the cells [5]. E. tarda could live and multiply in macrophages, and escape from the cells. It is important for the bacterium to lead to extra intestinal diseases and systemic infections [6]. E. tarda is capable to detoxify ROS by generating catalase (Kat) and superoxide dismutase (Sod) to survive within macrophages [7,8]. Okuda et al. suggested that the bacterial type III secretion system is able to interfere with the formation of acid stress in phagosomes to facilitate its replication in macrophages [9]. However, little other information is available about how E. tarda is affected by an acidic environment.Some findings have been reported about the changes that occur in other intracellular pathogens in response to acid stress in macrophages. For example, Rathman et al. suggested that an acidic environment in Salmonella-containing phagosomes is necessary for the bacterial survival and replication within the macrophage [10]. Supporting this finding, ...