Research identifies new family of marine 'megaphages'

Researchers from the Universities of Leicester, Warwick, Nottingham, Plymouth and the Marine Biological Association have sequenced the largest genome of its type within a newly-discovered family of ocean-dwelling bacteriophages, from water in the English Channel.

Bacteriophages -- referred to in this instance as 'megaphages' due to the extreme size of their genomes -- are viruses which prey on bacteria, and are the most abundant biological entities on Earth.

Following study of the predicted function of the genes, the researchers speculate that these megaphages could potentially alter the metabolism of their as-yet-unknown host in the marine environment.

Since ocean bacteria are known to play a major role in the cycling of carbon and nitrogen -- 50% of the oxygen we breathe comes from the oceans via carbon fixation -- these newly-identified megaphages are thought to potentially play an important role in this process.

Dr Andrew Millard, Associate Professor of Bacteriophage Bioinformatics at the University of Leicester and corresponding author for the study published in ISME Communications, said:

"From our previous work on cyanophages, we know phages have important roles in biogeochemical cycling. Finding these very large genomes with auxiliary metabolic genes, further highlights how phages may impact biogeochemical cycles.

"To understand the role of these megaphages, we now need to culture them to study them further."

Researchers studied these new bacteriophages using a combination of Illumina and MinION sequencing. While the majority of known phages contain genomes smaller than 200 kb, one of these megaphages -- dubbed Mar_Mega_1 -- showed a genome of more than 650 kb in length, making it one of the largest phage genomes assembled to date. The largest known megaphage genome is 735 kb in length.

Using phylogenetic and genomic analyses, researchers showed Mar_Mega_1 is distantly related to other megaphages previously found in the guts of humans, and based on current standards, represents a new family of phages in the marine environment.