Cyanophage auxiliary metabolic protein NblA is directly involved in phycobilisome degradation in infected marine cyanobacteria

Marine unicellular cyanobacteria are photosynthetic prokaryotes. They are widespread in every aquatic niche on Earth as they are responsible for ~25% of the fixed carbon that integrates into the ocean biosphere. Cyanophages are viruses infecting cyanobacteria. They are important players in the global food web, influencing their host diversity and shaping the cyanobacteria population due to their lytic properties. Therefore, they reduce significantly the world`s ocean biomass by inducing their host lysis, affecting geochemical cycles in oceans and lakes. Marine cyanophages often carry auxiliary metabolic genes (AMGs) that were acquired from their hosts by horizontal gene transfer. These viral genes often involved in photosynthesis and other cell metabolism processes. One of the genes found in viruses is nblA, which encodes for a small protein and it is known to induce degradation of the gigantic light-harvesting antennae complex called phycobilisome (PBS), as a part of a survival mechanism of the cyanobacterium.

Until recently nblA was reported to be present only in freshwater environments. We have found that cultured marine cyanophages carry the nblA gene, and with a new technique for mutating phage genomes, we deleted the cyanophage nblA gene in order to gain insight into about the role these proteins play on viral fitness. Using the phage nblA deletion mutant we found that cyanophages utilize their NblA during infection for targeted PBS degradation which significantly advances the course of the infection.