New lipid envelope-containing dsDNA virus isolates infecting Micromonas pusilla reveal a separate phylogenetic group

Abstract

Combined, these characteristics allowed classification of the MpVs into two groups.Exposure to chloroform led to loss of infectivity by all MpVs in one group, which suggests the presence of an outer lipid envelop. In addition, all except one of the members in that group formed a monophylogenetic clade that was distinct from all 35 other MpV isolates. The distinctive characteristics of the two MpV groups suggest different infection strategies, which may have important implications for the ecology of both host and virus populations in the environment. Knowledge gained from our study adds value to the MpV isolates as a scientific resource as it will aid in developing and testing in the laboratory new hypotheses about the ecological and 40 biogeochemical implications of M. pusilla viral infection in the environment.-3 -

Temperature is a key factor in Micromonas–virus interactions

“…At temperatures lower than T opt , MicV-B propagated and killed their hosts through cell lysis as classically reported in the literature (Mayer and Taylor, 1979;Zingone et al, 2006;Baudoux et al, 2015;Martínez-Martínez et al, 2015). Yet the kinetics and the intensity of viral replication slowed down with decreasing temperatures.…”

“…These approaches have shown that temperature may influence the infection process by regulating viral abundance and infectivity. Most marine virus isolates tolerate low temperatures whereas increasing temperatures tend to induce loss in infectivity and ultimately inactivation of the viral particles (Nagasaki and Yamaguchi, 1998;Baudoux and Brussaard, 2005;Tomaru et al, 2005;Martínez-Martínez et al, 2015). Nevertheless, as viruses generally exhibit a broader thermotolerance than their hosts (Mojica and Brussaard, 2014), and because the optimal temperature for lytic replication (i.e.…”

“…Previous studies demonstrated that Micromonas viruses (MicVs) are ubiquitous, highly dynamic and induce substantial mortality through cell lysis events in natural and cultured populations Suttle, 1991, 1995;Sahlsten, 1998;Zingone et al, 1999;Evans et al, 2003;Baudoux et al, 2015). The majority of known MicVs are lytic dsDNA viruses affiliated to the Phycodnaviridae family and the genus Prasinovirus (Mayer and Taylor, 1979;Cottrell and Suttle, 1991;Zingone et al, 2006;Martínez-Martínez et al, 2015), which may represent the most abundant viruses of eukaryotic marine plankton (Hingamp et al, 2013;Yau et al, 2015). Micromonas is among the phytoplankters that shows the widest latitudinal distribution on Earth and thereby inhabits waters with contrasted temperatures.…”

“…Members of this prominent genus are distributed in three discrete genetic clades (Guillou et al, 2004;Foulon et al, 2008) that are all susceptible to viral infection (Baudoux et al, 2015;Martínez-Martínez et al, 2015). Previous studies demonstrated that Micromonas viruses (MicVs) are ubiquitous, highly dynamic and induce substantial mortality through cell lysis events in natural and cultured populations Suttle, 1991, 1995;Sahlsten, 1998;Zingone et al, 1999;Evans et al, 2003;Baudoux et al, 2015).…”

Phytoplankton Virus Production Negatively Affected by Iron Limitation

“…In short, samples were diluted 200-1000-fold using a 2 M TrisHCl buffer at pH 8 and viruses were stained using the nucleic acid-specific fluorescent dye SYBR Green I (Molecular Probes R , Life Technologies, Thermo Fisher). Raw data were analyzed using Cytowin (Vaulot, 1989;Version 4.31 available at http:// application.sb-roscoff.fr/Phyto/index.php), whereby PgV and MpV were easily discriminated by plotting green nucleic acidspecific fluorescence vs. side scatter (Baudoux and Brussaard, 2005;Martínez et al, 2015).…”