Abstract
An uncultured non-photosynthetic basal lineage of the Cyanobacteria, the Melainabacteria, was recently characterised by metagenomic analyses of aphotic environmental samples. However, a predatory bacterium, Vampirovibrio chlorellavorus, originally described in 1972 appears to be the first cultured representative of the Melainabacteria based on a 16S rRNA sequence recovered from a lyophilised co-culture of the organism. Here, we sequenced the genome of V. chlorellavorus directly from 36 year-old lyophilised material that could not be resuscitated confirming its identity as a member of the Melainabacteria. We identified attributes in the genome that likely allow V. chlorellavorus to function as an obligate predator of the microalga Chlorella vulgaris, and predict that it is the first described predator to use an Agrobacterium tumefaciens-like conjugative type IV secretion system to invade its host. V. chlorellavorus is the first cyanobacterium recognised to have a predatory lifestyle and further supports the assertion that Melainabacteria are non-photosynthetic.
Highlights
Predatory microorganisms attack and digest their prey, which can be either bacteria or microbial eukaryotes (Coder & Starr, 1978; Stolp & Starr, 1963)
Genome summary A total of 701.2 Mbp of shotgun sequence data (2 × 300 bp paired-end Illumina) was obtained from DNA extracted from a co-culture of Vampirovibrio chlorellavorus and Chlorella vulgaris (NCIB 11384)
Ordination of the data by GC content and mapping read depth revealed a high coverage cluster of contigs comprising ∼94% of the data (Fig. S1). These contigs were inferred to belong to V. chlorellavorus by the presence of a 16S rRNA gene on one of the contigs and low coverage contigs were inferred to belong to the C. vulgaris by best matches to reference Chlorella genomes
Summary
Predatory microorganisms attack and digest their prey, which can be either bacteria or microbial eukaryotes (Coder & Starr, 1978; Stolp & Starr, 1963). They have been found in a range of environments, including terrestrial, freshwater, estuaries, oceans, sewages and animal faeces (Jurkevitch, 2007). Microbial predators have been classified as obligate (unable to grow in the absence of prey) or facultative (able to grow as a pure culture without the presence of prey).
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