Comparative analysis of differentially expressed genes in Acanthamoeba after ingestion of Legionella pneumophila and Escherichia coli

Acanthamoeba spp. feeds on bacteria, fungi, and algae to obtain nutrients from the environment. However, several pathogens can survive and multiply in Acanthamoeba. Mechanisms necessary for the survival and proliferation of microorganisms in Acanthamoeba remain unclear. The object of this study was to identify effective factors for the survival of microorganisms in Acanthamoeba. Differentially expressed genes (DEGs) in A. castellanii infected by Legionella pneumophila or Escherichia coli were identified based on mRNA sequencing. A total of 2342 and 1878 DEGs were identified in Acanthamoeba with L. pneumophila and E. coli, respectively. Among these DEGs, 502 were up-regulated and 116 were down-regulated in Acanthamoeba infected by L. pneumophila compared to those in Acanthamoeba feed on E. coli. Gene ontology analysis showed that the genes encoded small GTPase-mediated signal transduction proteins in the biological process domain, intracellular proteins in the cellular component domain, and ATP binding proteins in the molecular function domain were up-regulated while integral components of membrane proteins in the cellular component domain were down-regulated in Acanthamoeba infected by Legionella compared to those in Acanthamoeba feed on E. coli. During endosymbiosis with Legionella, Acanthamoeba showed various changes in the expression of genes supposed to be involved in phagosomal maturation. Acanthamoeba infected by Legionella also showed high expression levels of aminotransferase, methyltransferase, and cysteine proteinase but low expression levels of RNA pseudouridine synthase superfamily protein and 2OG-Fe(II) oxygenase superfamily. These results provide directions for further research to understand the survival strategy of L. pneumophila in A. castellanii.