UNIVERSITY OF HAWAI‘I AT HILO ◆ HOHONU 2020 ◆ VOL. 18 role in the health of our oceans. The ecological roles and behaviors of marine viruses drive evolu- Rachel Willard tion, shape populations and ecosystems, and with English 225 advances in technology, can potentially be used in Abstract the near future to increase the health of our oceans Marine viruses have played a critical role in and prevent marine life and habitat loss caused by the development of life on our planet. They are of- climate change. ten seen negatively as disease pathogens, but their About Marine Viruses ecological roles and behaviors have played a ma- Viruses are found virtually everywhere on the jor role in the evolution of all species, they have planet and are abundant around any forms of life. shaped populations and ecosystems, and have many important uses and relationships with their of energy consumption, being capable of growth, hosts. Their vast abundance and diversity have adapting to surroundings, responding to external shaped whole ecosystems and drive population forces, reproducing, and most importantly, be- rates in organisms such as marine microbes to cor- ing composed of at least a single cell (Lloyd 11). als and pilot whales. They have been seen to have a Following these rules, these loose strands of ge- mutualistic symbiotic relationship with corals, sea slugs, and many other marine organisms. Marine but they are the most abundant and diverse bio- viruses reduce the harmful plankton populations logical entities in the ocean (Suttle 2007). In the in algal blooms. They play a very important role 1980s, scientists estimated the amount of marine in the stabilization of ocean ecosystems through viral bodies in one milliliter of seawater to be well biogeochemical and nutrient cycling. over a million using electron microscopy (Suttle 2005). And being biological entities, viruses have Vira. Structure and Reproduction Viruses are very small particles ranging from 20 nanometers to no longer than 200 nanometers. Some of the smallest known viruses contain only three to four genes in their DNA or RNA (Bidle 1). Their true origin is unknown, but it is clear that viruses did not evolve from cells (Suttle 2013). Viruses have a fairly simple structure, being com- posed of a core containing RNA (single-stranded) or DNA (double-stranded) nucleic acids surround- ed by a coat of proteins and sometimes lipids called a capsid (Fuhrman 1). Some viruses may have a membrane layer called an envelope surrounding the capsid. Capsids can occur in an icosahedral, - sids have 20 triangular faces. Filamentous are long, rod- or helical-shaped. Head-tail forms con- (Fuhrman 542) Introduction tail. Their structures have evolved for best surviv- The word virus tends to hold a negative conno- al, dependent on their ability to infect a select host. tation. But like Joan Jett in 1981, viruses probably Viruses have “no intrinsic metabolism, [and func- don’t give a damn about their bad reputation (Jett). tion] only as parasites through cellular machin- We may not know much about marine viruses to- ery of a host organism” (Fuhrman 541). Viruses day, but we do know they play a very important 154 UNIVERSITY OF HAWAI‘I AT HILO ◆ HOHONU 2020 ◆ VOL. 18 host organism: bacteria (bacteriophage), plants, or measure because viruses do not have a universally animals. Microbes are the most common host to conserved gene like the ribosomal DNA genes in a marine virus because of their abundance, espe- cellular organisms, and because most viral hosts cially in the oceans. Viruses are able to reproduce - through a process known as lytic infection where dance and diversity of marine viruses have created they enter a host cell, create a copy of their DNA/ important roles in ocean productivity and biogeo- RNA and the host cell potentially bursts or lyses. chemical cycles. History of Virology Viral abundance is possible partially because “In the human world, viruses will continue to of their evolutionary ability to adapt to harsh, oxy- have a lousy reputation thanks to the traumatic gen and nutrient poor environments. While most impact of a few devastating infections that have viruses will be found closer to the water’s surface, plagued humans throughout recorded history,” some impressive marine viruses have adapted to Christopher Lloyd says in The Story of the World live and even thrive in harsh areas such as deep- in 100 Species (Lloyd 15). We have barely start- sea hydrothermal vents. These deep-sea hydro- ed to scratch the surface of understanding marine thermal vents, typically found along tectonically viruses. The study of viruses, known as virology, active mid-ocean ridges, can reach extreme tem- has shed much light on the behavior and ecologi- peratures up to 400°C, or 752°F (Ortman 1516). cal roles of marine viruses over the past few de- Surprisingly, there are other forms of life in these cades. Virology exponentially advanced with the vents. The marine viruses are supported by an invention of the transmission electron microscopy abundance of chemosynthetic and heterotrophic (TEM). This gave scientists the ability to distin- prokaryotes that become their hosts. guish viruses from other microbial forms and to Driving Evolution and Shaping Whole see their vast abundance. Before TEMs, “viruses Ecosystems were not regarded as quantitatively important Viruses are able to drive evolution in terms components of marine food webs until they were of their host cells, developing defense strategies shown by direct counts to be highly abundant” against viral lytic infections over millions and mil- (Fuhrman 541). Up until the 1990s, marine viral lions of years. This cycle of host cells and virus- infections were not seen to play such a major role es, both adapting to attack or defend, has led to with oceanic ecosystems and processes. Mathias incredible evolution in host cells (Middelboe 4). Middelboe argues that “the large number of un- The evolution of both host cells and viruses has known viral populations in the marine metage- made viruses capable of infecting life of all sizes. nome emphasizes the need for further isolation, Different classes and species of marine viruses can infect single-celled bacteria all the way up to the viruses” (Middelboe 1). largest marine mammals. Diversity and Abundance Pilot Whales Viruses are incredibly widespread and diverse. Every cellular organism on the planet is suscep- pilot whale showed the success of the virus and its tible to viral infection by at least one type of virus. capability of infecting multiple advanced species. This implies that viruses are the most diverse of The research team was only able to collect a virus all biological entities on the planet (Fuhrman 541). with a partial genome sequence from the diseased Viruses are especially diverse and abundant in the pilot whale, but they were able to distinguish it as an oceans. Curtis Suttle calculated that “if we compare the number of viruses in the oceans to the num- and genus This genus of virus is bers of stars in the universe, there are about 10²³ capable of infecting seagulls, terns, waders, and stars in the universe. In contrast, there are about 10 other marine mammals, like pinnipeds and other million-fold more viruses in the ocean than there - are stars in the universe… [approximately] 1030 rus in the pilot whale was likely spread by contact viruses in the ocean” (Suttle 2013). Although ma- with a seabird while the whale was at the surface rine viruses are so abundant, diversity is “hard to (Groth 183). 155 UNIVERSITY OF HAWAI‘I AT HILO ◆ HOHONU 2020 ◆ VOL. 18 Anthozoans worldwide ecosystems “other than as purveyors of It is well known that “the health of coral reefs disease, and if it were not for viruses, life on the is declining on a global scale” (Weynberg 2015). planet would probably not exist” (Suttle 2013). Different diseases, including white plague coral Viruses are used in many unseen ways in our lives, disease, are a rampant cause of death and bleach- like cheeses and other dairy products being treated ing for reefs worldwide. Cnidarian viruses are “the with certain viruses to prevent bacterial growth and least-studied constituents in the coral holobiont” mold. Some viruses have attained important mutu- (Marhaver 2277), meaning there is much to be re- alistic symbiotic relationships with their host organ- searched and learned. Only recently have scientists ism, including bacteria, insects, plants, fungi, and discovered that a herpes-like virus plays a key role animals (Roossinck 99). in plagued reefs in the Caribbean (Soffer 271), al- Symbiotic Relationships though bacteria are also suspected to play a role. Marine viruses play a notably important and Metagenomic analyses of the coral and its symbi- - otic algae, zooxanthellae, showed that a sequence lobionts. Kristin Marhaver explains this unlikely for the herpes-like virus counted for 4-8% of the mutualistic symbiosis: total microbial sequencing (Marhaver 2277). As Viruses can serve as a stabilizing force for sym- detrimental as viruses can be to corals and reef eco- bioses by establishing addiction systems within a systems, they have been found to play a necessary host. For example, zooxanthellae infected with a role in healthy corals’ lives. latent virus are resistant to lysis by VLP [virus-like Bacteriophages and Eukaryotic Microbe Viruses particles]. Phages may also stabilize symbioses. For Microbes such as bacteria, archaea, and eu- Hamiltonella defensa, karyotic organisms are a huge source of food in a bacterial symbiont of the pea aphid, produces a the oceans and the most popular host for a virus. toxin that appears to protect host aphids from eu- Bacteriophages, or phages, are viruses that have karyotic parasites. The diversity of constituents in adapted to infecting bacterial and archaeal cells for the coral holobiont elevates the potential for these replication.