Abstract
Phage satellites are mobile genetic elements that parasitize viruses, exerting profound biological and ecological impacts. Phage satellites are known to infect several gram-positive genera and a few gram-negative bacterial species, most associated with the human microbiome. Direct inspection of “wild” virus particles, however, revealed that marine phage satellites are widely distributed and abundant in the global oceans. Their genetic diversity, gene repertoires, and host ranges appear much greater than has been previously reported. Genetic analyses now provide clues about the parasitic life cycles, helper bacteriophage interactions, and reproductive strategies of these newly recognized marine phage satellites. Their properties, diversity, and environmental distributions suggest they may exert substantial influence on microbial ecology and evolution in the sea.
Phage satellites are mobile genetic elements that propagate by parasitizing bacteriophage replication. We report here the discovery of abundant and diverse phage satellites that were packaged as concatemeric repeats within naturally occurring bacteriophage particles in seawater. These same phage-parasitizing mobile elements were found integrated in the genomes of dominant co-occurring bacterioplankton species. Like known phage satellites, many marine phage satellites encoded genes for integration, DNA replication, phage interference, and capsid assembly. Many also contained distinctive gene suites indicative of unique virus hijacking, phage immunity, and mobilization mechanisms. Marine phage satellite sequences were widespread in local and global oceanic virioplankton populations, reflecting their ubiquity, abundance, and temporal persistence in marine planktonic communities worldwide. Their gene content and putative life cycles suggest they may impact host-cell phage immunity and defense, lateral gene transfer, bacteriophage-induced cell mortality and cellular host and virus productivity. Given that marine phage satellites cannot be distinguished from bona fide viral particles via commonly used microscopic techniques, their predicted numbers (∼3.2 × 1026 in the ocean) may influence current estimates of virus densities, production, and virus-induced mortality. In total, the data suggest that marine phage satellites have potential to significantly impact the ecology and evolution of bacteria and their viruses throughout the oceans. We predict that any habitat that harbors bacteriophage will also harbor similar phage satellites, making them a ubiquitous feature of most microbiomes on Earth.
Collapse