Abstract
ABSTRACTMost virus-infected cells show morphological and behavioral changes, which are called cytopathic effects. Acanthamoeba castellanii, an abundant, free-living protozoan, serves as a laboratory host for some viruses of the phylum Nucleocytoviricota—the giant viruses. Many of these viruses cause cell rounding in the later stages of infection in the host cells. Here, we show the changes that lead to cell rounding in the host cells through time-lapse microscopy and image analysis. Time-lapse movies of A. castellanii cells infected with Mimivirus shirakomae, kyotovirus, medusavirus, or Pandoravirus japonicus were generated using a phase-contrast microscope. We updated our phase-contrast-based kinetic analysis algorithm for amoebae (PKA3) and used it to analyze these time-lapse movies. Image analysis revealed that the process leading to cell rounding varies among the giant viruses; for example, M. shirakomae infection did not cause changes for some time after the infection, kyotovirus infection caused an early decrease in the number of cells with typical morphologies, and medusavirus and P. japonicus infection frequently led to the formation of intercellular bridges and rotational behavior of host cells. These results suggest that in the case of giant viruses, the putative reactions of host cells against infection and the putative strategies of virus spread are diverse.IMPORTANCE Quantitative analysis of the infection process is important for a better understanding of viral infection strategies and virus-host interactions. Here, an image analysis of the phase-contrast time-lapse movies displayed quantitative differences in the process of cytopathic effects due to the four giant viruses in Acanthamoeba castellanii, which were previously unclear. It was revealed that medusavirus and Pandoravirus japonicus infection led to the formation of a significant number of elongated particles related to intercellular bridges, emphasizing the importance of research on the interaction of viruses with host cell nuclear function. Mimivirus shirakomae infection did not cause any changes in the host cells initially, so it is thought that the infected cells can actively move and spread over a wider area, emphasizing the importance of observation in a wider area and analysis of infection efficiency. These results suggest that a kinetic analysis using the phase-contrast-based kinetic analysis algorithm for amoebae (PKA3) reveals the infection strategies of each giant virus.
Highlights
IMPORTANCE Quantitative analysis of the infection process is important for a better understanding of viral infection strategies and virus-host interactions
To reveal the changes that occur in A. castellanii cells due to infection by different giant viruses, time-lapse movie recording and image analysis were performed for A. castellanii cells infected with the four viruses, kyotovirus, M. shirakomae, medusavirus, and P. japonicus
And in the figures, mimivirus refers to M. shirakomae, pandoravirus refers to P. japonicus, and control refers to the uninfected A. castellanii cells
Summary
IMPORTANCE Quantitative analysis of the infection process is important for a better understanding of viral infection strategies and virus-host interactions. The new algorithm was used to analyze A. castellanii infected with four types of giant viruses, kyotovirus of the Marseilleviridae family [10], Mimivirus shirakomae of the Mimiviridae family [18], medusavirus [8], and Pandoravirus japonicus of the Pandoraviridae family [19] isolated in Japan Infection with these viruses is known to cause cell rounding in A. castellanii. A. castellanii infected with M. shirakomae undergoes cell lysis, and A. castellanii infected with medusavirus undergoes cyst formation It is unknown whether the host cells infected with these viruses display different morphological and behavioral characteristics during the infection process that lead to cell rounding. This is because the individual cells could not be identified within the aggregates, and the morphology of a single cell could not be compared with that of the other viruses
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