First evidence of host range expansion in virophages and its potential impact on giant viruses and host cells

Said Mougari; Nisrine Chelkha; Dehia Sahmi-Bounsiar; Fabrizio Di Pinto; Philippe Colson; Jonatas Abrahao; Bernard La Scola

Clearly, according to the PCR product intensity, after several passages with Tupanvirus, the amount of mutant Guarani DNA evolved to decrease (Fig. 4a) . Such a decrease was not observed in the control (Fig. 4b) . These results are intriguing given the high replication efficiency of the mutant genotype observed with Tupanvirus Deep Ocean (Fig. 2a) . At the same time, we noticed a progressive increase in the host cell population survival over the passages (data not shown). This probably raises questions regarding the virulence of the mutant genotype toward its new virus host, Tupanvirus. Indeed, it is known from our previous study that Guarani impaired the infectivity of its viral host APMV, resulting in a decrease in amoebae lysis 24 . Nevertheless, as this is the first time that we describe a host range expanding mutation in virophage, we expected the mutant genotype to have a distinct virulent profile toward its novel virus host than the wild-type strain toward APMV. To test this hypothesis, we first started by studying the evolution of Tupanvirus infectious particle production during a passage experiment in the presence of mutant Guarani. Figure 4c shows Tupanvirus titers during a ten-passage experiment in the presence of the virophage measured by end-point dilution method. Prior to end point dilution, the virus supernatant was submitted to heat treatment at 55°C for 30 min 34 . This treatment efficiently inactivated the mutant virophage without reducing the titer of viable virus particles ( Supplementary Fig. 2 ). We found that infection with the mutant strain severely modifies the trajectory of Tupanvirus in the model.