Resistance in marine
cyanobacteria against infection bygeneralist and specialist cyanophages
Cyanobacteria of the genera Synechococcus and Prochloroccocus areinfected by generalist and specialist phages. Coexistence between thecyanobacteria and the phages is thought to be facilitated by resistance. Whileextracellular resistance is established, it not known if intracellularresistance exists in marine cyanobacteria. In order to investigate whetherintracellular resistance exists in Prochlorococcus and Synechococcusandif resistance differs against generalist and specialist cyanophages wechecked if infections of resistant strains are halted inside or outside thecell. Resistance was extracellular in most interactions against specialist cyanophages. Incontrast, resistance was intracellular in practically all interactions againstgeneralist cyanophages.This unveils a heavy cost of promiscuous entry of generalist phages intonon-host cells that is rarely paid by specialists. Furthermore, the stage ofintracellular arrest was interaction-specific, halting at various stages of theinfection cycle. This indicates the presence of potential differentintracellular mechanismsofresistance. Searching the genome of marine Synechococcus and Prochloroccocusstrains for genes of known defense systems showed that complete systems arerare. Inactivation of two known systems in SynechococcusWH5701did not result in sensitivity. Finally, we found that in SynechococcusWH5701the mechanism of resistance was loss of transaction of tRNAgenesthat appear to be crucial for translation of phages proteins.
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