T4 genes in the marine ecosystem: studies of the T4-like cyanophages and their role in marine ecology

Abstract

From genomic sequencing it has become apparent that the marine cyanomyoviruses capable of infecting strains of unicellular cyanobacteria assigned to the genera Synechococcus and Prochlorococcus are not only morphologically similar to T4, but are also genetically related, typically sharing some 40-48 genes. The large majority of these common genes are the same in all marine cyanomyoviruses so far characterized. Given the fundamental physiological differences between marine unicellular cyanobacteria and heterotrophic hosts of T4-like phages it is not surprising that the study of cyanomyoviruses has revealed novel and fascinating facets of the phage-host relationship. One of the most interesting features of the marine cyanomyoviruses is their possession of a number of genes that are clearly of host origin such as those involved in photosynthesis, like the psbA gene that encodes a core component of the photosystem II reaction centre. Other host-derived genes encode enzymes involved in carbon metabolism, phosphate acquisition and ppGpp metabolism. The impact of these host-derived genes on phage fitness has still largely to be assessed and represents one of the most important topics in the study of this group of T4-like phages in the laboratory. However, these phages are also of considerable environmental significance by virtue of their impact on key contributors to oceanic primary production and the true extent and nature of this impact has still to be accurately assessed.

Genomics of Bacterial and Archaeal Viruses: Dynamics within the Prokaryotic Virosphere

“…(Reproduced from reference 158. ) thought to modulate virus-host interactions, assisting in the adaptation of viruses to new hosts and/or environments (53,181). Virus-encoded components of the photosynthetic machinery represent one of the best examples of such fitnessconferring functions.…”

“…Notably, whereas the level of expression of the host photosynthetic genes declined over the course of infection, the level of transcription of the viral counterparts steadily increased (164). psbA and psbD are not the only photosynthesis-related genes in cyanophage genomes: proteins which may potentially influence everything from adaptation to light stress, light harvesting, photosystem stability, and photosynthetic electron transport are sporadically encoded by different cyanophages (52,53). Other noncore genes of cyanophages include those associated with carbon, phosphate, and nitrogen metabolism; the phosphate stress response; nucleotide metabolism; vitamin B 12 and lipopolysaccharide biosynthesis (53,264,265,287); and, as recently revealed through metagenomic data mining, antioxidation, the assembly of Fe-S clusters, and translation (249).…”

“…Other noncore genes of cyanophages include those associated with carbon, phosphate, and nitrogen metabolism; the phosphate stress response; nucleotide metabolism; vitamin B 12 and lipopolysaccharide biosynthesis (53,264,265,287); and, as recently revealed through metagenomic data mining, antioxidation, the assembly of Fe-S clusters, and translation (249). Although the exact role of the proteins encoded by these noncore genes is currently not known, their widespread distribution in cyanophage genomes does suggest that they are likely to increase virus fitness and drive adaptation to particular hosts and environments (53). Furthermore, the abundance of "cellular" genes in viral genomes might have a significant impact on the evolutionary dynamics of these genes not only within the virus population but also in their hosts.…”

“…psbA and psbD are not the only photosynthesis-related genes in cyanophage genomes: proteins which may potentially influence everything from adaptation to light stress, light harvesting, photosystem stability, and photosynthetic electron transport are sporadically encoded by different cyanophages (52,53). Other noncore genes of cyanophages include those associated with carbon, phosphate, and nitrogen metabolism; the phosphate stress response; nucleotide metabolism; vitamin B 12 and lipopolysaccharide biosynthesis (53,264,265,287); and, as recently revealed through metagenomic data mining, antioxidation, the assembly of Fe-S clusters, and translation (249). Although the exact role of the proteins encoded by these noncore genes is currently not known, their widespread distribution in cyanophage genomes does suggest that they are likely to increase virus fitness and drive adaptation to particular hosts and environments (53).…”

Polar freshwater cyanophage S-EIV1 represents a new widespread evolutionary lineage of phages

“…PCC6803 with reduced spermidine content exhibits reduced psbA2 transcript stability (Mulo et al, 1998). SpeD is also commonly found in marine T4-like cyanophage genomes (Clokie et al, 2010;Ignacio-Espinoza and Sullivan, 2012 (Storz et al, 1990). During starvation, when the ability to cope with environmental stress is compromised by the lack of nutrients, DPS efficiently and rapidly responds to oxidative and nutritional stresses by making cells more resistant to reactive oxygen (Storz et al, 1990;Farr and Kogoma, 1991;Martinez and Kolter, 1997).…”