Rumen Virus Populations: Technological Advances Enhancing Current Understanding

Abstract

The rumen contains a multi-kingdom, commensal microbiome, including protozoa, bacteria, archaea, fungi and viruses, which enables ruminant herbivores to ferment and utilize plant feedstuffs that would be otherwise indigestible. Within the rumen, virus populations are diverse and highly abundant, often out-numbering the microbial populations that they both predate on and co-exist with. To date the research effort devoted to understanding rumen-associated viral populations has been considerably less than that given to the other microbial populations, yet their contribution to maintaining microbial population balance, intra-ruminal microbial lysis, fiber breakdown, nutrient cycling and genetic transfer may be highly significant. This review follows the technological advances which have contributed to our current understanding of rumen viruses and drawing on knowledge from other environmental and animal-associated microbiomes, describes the known and potential roles and impacts viruses have on rumen function and speculates on the future directions of rumen viral research.

Keywords: biofilm; metagenomics; methanogen; phage; proteomics; rumen; virus.

FIGURE 1

Transmission electron microscopy illustrating examples of common rumen virus morphotypes including Siphoviridae (A–E), Myoviridae (F–I), Podoviridae (J–O) and other virus-like-particles including potentially non-tailed phages (P–S), such as Corticoviridae and Microviridae (scale bar 200 nm). All virus particles were purified from a single sample collected from an in vitro fermentation system (Infors) started with bovine rumen fluid. Virus particles were fixed with 2.5% glutaraldehyde and stained with 1% ammonium molybdate pH 7.0 and viewed with a JEOL JEM1400 Transmission Electron Microscope. Micrographs were captured using a Gatan Orius CCD camera.

FIGURE 2

(A) Potential roles of prokaryote viruses in microbial ecology and evolution. (B) Potential roles of prokaryote viruses in biofilms.

FIGURE 3

Potential mechanisms for spread of rumen viruses. Viruses may be spread by aerosols, saliva and fecal shedding, with viral particles moving between animals (maternal and within herd interactions) and their environment (water, feed, housing and infrastructure).