10 Features June 2011 © 2011 The Biochemical Society Marine Biology Key words: coccolitho- virus, Emiliania huxleyi, phytoplankton, saxitoxin, virus, zombifcation Silent killers The biochemistry of the undead The Earth’s oceans are teeming with life. Despite our obsession with the terrestrial environment we inhabit, it is the oceans that frst gave rise to life 2.9 billion years ago, and, with an extra billion years or so of evolution behind them, it is the oceans that harbour the greatest genetic and metabolic diversity on the planet. Yet we know surprisingly little about the biochemistry of our oceans. Microbial life forms covering the three cellular kingdoms (Archaea, Bacteria and Eukarya) represent by far the largest fraction of the total biomass existent in the oceans. However, a poorly studied and, until recently, largely ignored other kingdom also exists: the viral kingdom. Entirely dependent on the three cellular kingdoms of life, the viral kingdom rules above with an iron fst, ruthlessly and mercilessly destroying their hosts in order to replicate and produce their own progeny. new viruses as possible until decay and rot sets in, leading to the disruption of cellular integrity. Softly, softly, catchee algae At the very bottom of the marine food chain, the phytoplank‑ ton, a large group of genetically diverse oxygen‑generating photosynthetic organisms (including cyanobacteria, micro‑ algae and seaweeds) fx CO 2 and convert it into organic compounds such as lipids, sugars and proteins. Teir im‑ portance cannot be underestimated: they are responsible for around half of the oxygen we breathe. Tey are quiet, unassuming, mostly single‑celled workers that ensure that life on Earth can exist. Te abundance of viruses in the water column ensures that viral infection has a massive impact on their community dynamics. When algal numbers are rela‑ tively low, all viruses can do is foat about in the water column It was only a few decades ago that the impact of this re‑ lentless killing activity was begun to be appreciated. Tis dawning realization was triggered by the discovery of an immense viral abundance in the oceans. Numbering in ex‑ cess of 10 million per ml of water (an estimated total of 10 31 viruses in the oceans) 1 , it was soon realized that the marine viruses were interacting with their cellular counterparts in the microbial kingdom on an unprecedented scale. With an estimated 10 23 new infections occurring every second within the ocean, viruses are estimated to kill up to 40% of marine bacteria on a daily basis 2 . Tis lytic function is of fundamental importance to global biogeochemical cy‑ cling and ecosystem function, which would undoubtedly collapse without the constant ‘lubrication’ of the planets biological machinery. Crucially, the impact of viral infection, when it is given consideration, is ofen studied from the end point: models are ofen interested only in the loss of cells and the cycling of nutrients. However, the journey may be just as important as the destination. With viral infection occurring on such a phenomenal scale, a signifcant proportion of microbial cells in the marine environment are infected at any given time. While on the surface these cells may look and act alive as they play host to the selfsh replicators within, in reality these cells have been handed a life sentence and are merely shadows of their former selves. Tey can be regarded as the ocean’s undead. Tese hapless host vessels are either lost entirely to the viral underworld or are in vicious intra‑ cellular battle for survival, and through their sheer abun‑ dance, contribute signifcantly to the biochemistry of the oceans. When the battle has been lost, zombifed cells mix alongside their healthy counterparts with their metabolic activities hijacked by the enemies within their walls as they move blindly through the motions of producing as many Mike Allen (Plymouth Marine Laboratory, UK) and António Pagarete (University of Bergen, Norway) Coccolithophores plus virus attached to lith Downloaded from http://portlandpress.com/biochemist/article-pdf/33/3/10/6856/bio033030010.pdf by guest on 01 October 2021