December 2014
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Environmental Microbiology
Acaryochloris marina is a symbiotic species of cyanobacteria that is capable of utilising far-red light. We report the characterisation of the phages A-HIS1 and A-HIS2, capable of infecting Acaryochloris. Morphological characterisation of these phages places them in the family Siphoviridae. However, molecular characterisation reveals that they do not show genetic similarity with any known siphoviruses. Whilst the phages do show synteny between each other, the nucleotide identity between the phages is low at 45-67 %, suggesting they diverged from each other some time ago. The greatest number of genes shared with another phage (a myovirus infecting marine Synechococcus) was four. Unlike most other cyanophages and in common with the Siphoviridae infecting Synechococcus no photosynthesis-related genes were found in the genome. CRISPR spacers from the host Acaryochloris had partial matches to sequences found within the phages, which is the first time CRISPRs have been reported in a cyanobacterial/cyanophage system. The phages also encode a homologue of the proteobacterial RNase T. The potential function of RNase T in the markup or digestion of crRNA hints at a novel mechanism for evading the host CRISPR system. This article is protected by copyright. All rights reserved.