Meet microbiologys newest genetic marker (RNRs and viral diversity)

The 16S rRNA gene is commonly used in marine microbiology as a genetic marker for a number of features. It’s highly conserved nature and presence across all taxa mean that it is key to the identification and classification of Bacteria and Archaea and provides vital information about their diversity. In spite of this, to date, no such phylogenetic marker has been associated with the marine virioplankton community. In fact, marker genes that provide insight into environmental viral diversity are thus far typically limited to specific viral taxa. However, a study by Sakowski et al may provide a gene analogous to 16S rRNA that reveals new insight into viral diversity.

The paper proposes the use of the genes for ribonucleotide reductases (RNRs) as a genetic marker for viral diversity due to the fact that it is widely distributed among diverse viral lineages (and therefore is evolutionarily ancient) and it is abundant within environmental viral assemblages. In addition to this the genes play an important role in viral biology, appear to have a single evolutionary origin and are phylogenetically informative. It should also be noted that they are well represented in reference databases. All of these criteria indicate that RNR gene products may be the ideal marker gene for marine viruses.

RNRs themselves are the only known enzymes capable of reducing ribonucleotides to deoxyribonucleotides which means they are an essential part of DNA synthesis. They are a key part of biosynthesis and have therefore been identified in most of the lytic marine phages which significantly influence nutrient cycles in the global ocean. RNRs are also biologically informative due to the fact that they form three classes according to reactivity with O₂ with each class being broadly indicative of certain viral characteristics. In fact the data from this study shows that RNR sequence diversity connects with phage morphological groups and can be predictive of ecological strategies used in the virioplankton.

The importance of this is that it provides insight into the ecological features of lytic phage populations. These viruses play a vital a vital role in marine ecosystems as top-down regulators of bacterial populations and agents of horizontal gene transfer. In addition to this they are key to marine nutrient cycling and yet little is understood about their diversity. Therefore, the thing to take away from this paper is really its methodology; by using RNR gene products as a proxy for phage population biology, it opens up a new way to investigate the marine viral community.

Sakowski, E. G, Munsell, E. V, Hyatt, M, Kress, W, Williamson, S. J, Nasko, D. J, Polson, S. W, and Wommack, K. E. (2014). Ribonucleotide reductases reveal novel viral diversity and predict biological and ecological features of unknown marine viruses. PNAS. 111, 15786-15791.