Analysis of the KDO biosynthetic cluster in CroV

Cafeteria roenbergensis virus (CroV) is a double-stranded DNA giant virus (692 kb) that infects the marine unicellular heterotrophic nanoflagellate C. burkhardae and it is the first giant virus reported to infect zooplankton1. Viruses should be seen as integral components of any ecosystem where they contribute to the maintenance of the balance between species and resources. Indeed, bacterivorous nanoflagellates such as C. burkhardae, make up a significant portion of the ocean’s protozoan communities. Unlike mammalian viruses (e.g. HIV-1, SARS-CoV-2), which exploit host-encoded enzymes to build glycans that echo those of the host, most giant viruses encode their own enzymes with the result that their polysaccharides differ from those produced by their hosts2. Gene annotation suggests that CroV encodes a partial Kdo biosynthetic pathway; each of the three viral proteins, crov265, crov266, crov267, presents a dual activity that in some cases (C-termini of crov266 and crov267) seem not to be related to CMP-Kdo production. This study aims to provide new insights into the CroV Kdo biosynthetic pathway by analysing the features of the encoded proteins by bioinformatic analysis.