TABLE 4.
Roles and characteristics of virus populations within the rumen, as suggested by previous studies of rumen virus populations, rumen microbes (bacteria and archaea) and viruses isolated from the rumen.
| Roles and characteristics of virus populations within the rumen | Example publications |
| Viruses are always present in high numbers and actively replicate in the microbial populations of the rumen. | Adams et al., 1966; Ritchie et al., 1970 |
| Viral replication and action of viral proteins causes lysis of microbial cells and the release of microbial proteins and nucleic acids, contributing to the intra-ruminal recycling of nutrients. | Nolan and Leng, 1972; Orpin and Munn, 1974; Wells and Russell, 1996; Solden et al., 2018 |
| Viruses are mobile genetic elements; they transfer genetic material between microbes and enable the stable integration of virus-encoded (prophage) genes into rumen microbial genomes. | Klieve et al., 1989; Cheong and Brooker, 1998; Attwood et al., 2008; Seshadri et al., 2018 |
| Virus populations drive microbial diversity through predation, causing episodes of microbial lysis and blooms of virus particles. | Hoogenraad et al., 1967; Iverson and Millis, 1977; Klieve and Swain, 1993 |
| Virus infection and development of resistance can cause changes in bacterial growth habit (e.g., increases in bacterial extracellular polysaccharide). | Klieve and Bauchop, 1991; Klieve et al., 1991 |
| Rumen viral population size and composition is dynamic, fluctuating in response to changes in microbial numbers and diet. | Swain et al., 1996a; Klieve et al., 1998; Anderson et al., 2017 |
| Rumen viruses are taxonomically diverse with the prokaryote virus order Caudovirales (tailed phages) being the most abundant. | Ritchie et al., 1970; Klieve and Bauchop, 1988; Berg Miller et al., 2012 |
| Viruses (specifically phages) tend to only infect specific rumen microbes (limited microbial host range). | Iverson and Millis, 1976a; Styriak et al., 1989; Klieve et al., 1999 |
| Virus particles (specifically phage particles) can be degraded with prolonged exposure to rumen fluid. | Iverson and Millis, 1976a; Smith et al., 1987; Nemcova et al., 1993 |
| Virus infection contributes to the development of genetic resistance mechanisms (e.g., CRISPR/Cas systems). | Berg Miller et al., 2012; Gilbert et al., 2017 |
| Viruses can interact with cells of the rumen epithelium (demonstrated in vitro). | Styriak et al., 1991 |