Protein secretion and encystation in Acanthamoeba

Abstract

Free-living amoebae (FLA) are protists of ubiquitous distribution characterised by their changing morphology and their crawling movements. They have no common phylogenetic origin but can be found in most protist evolutionary branches. Acanthamoeba is a common FLA that can be found worldwide and is capable of infecting humans. The main disease is a life altering infection of the cornea named Acanthamoeba keratitis. Additionally, Acanthamoeba has a close relationship to bacteria. Acanthamoeba feeds on bacteria. At the same time, some bacteria have adapted to survive inside Acanthamoeba and use it as transport or protection to increase survival. When conditions are adverse, Acanthamoeba is capable of differentiating into a protective cyst. This study had three objectives. First, isolate and identify new FLA and Acanthamoeba strains. Second, identify encystation factors of Acanthamoeba. Third, identify and characterise new potential antimicrobial proteins produced by Acanthamoeba. The isolation of environmental amoebae was performed, and several strains of Acanthamoeba were identified from previously known genotypes. Also, two new species of FLA were identified: Allovahlkampfia minuta and Leptomyxa valladaresi. The dynamics of encystment were studied in different strains of Acanthamoeba. RNAseq was used to study gene expression during differentiation and identify differentially expressed genes. We identified different encystment factors including at least two encystment related proteases. A new antimicrobial zymogram was developed that identified antimicrobial proteins being secreted by Acanthamoeba. A 33 kDa protease was found to be able to lyse bacteria. We created DNA constructs encoding the protease and a lysozyme from Acanthamoeba for heterologous expression. The genes were successfully cloned.

However, bacteria were not able to produce the proteins most probably due to their antimicrobial characteristics. Further studies are required regarding encystment and antimicrobial factors identified. Such experiments should help elucidate critical factors of Acanthamoeba’s biology that could help treat several infections.