Adaptive evolution of viruses infecting marine microalgae (haptophytes), from acute infections to stable coexistence

Abstract

Collectively known as phytoplankton, photosynthetic microbes form the base of the marine food web, and account for up to half of the primary production on Earth. Haptophytes are key components of this phytoplankton community, playing important roles both as primary producers and as mixotrophs that graze on bacteria and protists. Viruses influence the ecology and diversity of phytoplankton in the ocean, with the majority of microalgae–virus interactions described as ‘boom and bust’ dynamics, which are characteristic of acute virus–host systems. Most haptophytes are, however, part of highly diverse communities and occur at low densities, decreasing their chance of being infected by viruses with high host specificity. Viruses infecting these microalgae have been isolated in the laboratory, and there are several characteristics that distinguish them from acute viruses infecting bloom‐forming haptophytes. Herein we synthesise what is known of viruses infecting haptophyte hosts in the ocean, discuss the adaptive evolution of haptophyte‐infecting viruses ‐from those that cause acute infections to those that stably coexist with their host ‐ and identify traits of importance for successful survival in the ocean.

Grazing on Marine Viruses and Its Biogeochemical Implications

“…In these highly proliferative environments, viral infection can lead to the termination of the bloom-forming host population and to the release of large numbers of viral particles ( 29 , 68 ). Although most NCVs seem to have a rather persistent abundance throughout the year ( 30 , 69 , 70 ), such “boom and bust” dynamics following host blooms may provide a temporarily abundant food source for the filter feeders among marine grazers. Furthermore, we posit that owing to their distinct structural characteristics, NCV particles can have a significant contribution to the marine DOM pool.…”

Current Status and Perspective on the Use of Viral-Based Vectors in Eukaryotic Microalgae

“…Recently, a list of 10 isolated and characterized viruses was published by Sandaa et al (2022) [180]. These viruses can infect marine haptophytes species.…”

“…To date, a total 63 virus that infect eukaryotic microalgae have been isolated and cultured in the laboratory, whereby 50.79% contain dsDNA as genomic material, 15.8% ssDNA, 1.58% dsRNA, and 22.2% ssRNA, whereas 7.93% have not yet been classified [ 163 , 179 ]. Recently, a list of 10 isolated and characterized viruses was published by Sandaa et al (2022) [ 180 ]. These viruses can infect marine haptophytes species.…”

Giant DNA Viruses Infecting Unicellular Protists

“…Th us, during viral infection, the metabolism of virus-infected cells undergoes enormous changes, which in turn can aff ect coexisting microbial communities and ecological processes. Structural and proteomic studies of the Aureococcus anophageff erens virus revealed that the structure, assembly, and some of the proteins packed inside the AaV particle are similar to those of other giant virus particles, but unlike them, AaV has no fi brils on the outside of its capsid, although fi brils are found on the surface of many viruses from various NCLDV families [52,53].…”

“…Limited information is available on the role of viruses infecting haptophytes occurring at lower abundances in the sea. It is believed that host populations must exceed a certain threshold density to sustain the virus population, which is true for CeV 01B and other viruses that infect non-fl owering strains, in particular H. ericina [53]. Viruses like CeV employ a variety of strategies to co-exist with their hosts, including a longer latent period and lower virulence, infectivity, and decay compared to viruses that cause acute lytic infection.…”