Many labs have worked with Halobacterium salinarum, and they either use the R1 strain or the NRC-1 strain. When the genomes of these two strains were reported in 2008 (Pfeiffer et al.), it showed they are so similar in sequence that they must have derived from the same isolate, but for various reasons it was not possible to identify that isolate. Here we used publicly available sequence data to hunt down the parent. See https://doi.org/10.1002/mbo3.1365. This is not a simple BLASTn comparison but rather a comprehensive analysis and includes a speculative outline of how the two strains ended up as we see them today.

Published in Microbial Resource Announcements in May, 2021 (doi: 10.1128/MRA.00226-21) this describes the genome of Hardyhisp2, a virus isolated in my lab way back in 1998! It came from a water sample of the hypersaline Lake Hardy, Victoria, Australia. As seen in the dot plot (above left) and genome map comparison (above right), the 16,133 bp linear dsDNA genome shows strong sequence similarity to the type species of gammapleolipovirus, His2. The most disparate gene appears to be the one encoding spike protein (VP1 spike), which is used by the virus for cell attachment, but both Hardyhisp2 and His2 infect the same host, Haloarcula hispanica. Perhaps they attach to different cell receptors. Characteristic of this viral genus, the Hardyhisp2 genome carries a gene encoding a protein-primed DNA polymerase, and also has inverted terminal repeats (shaded grey in the figure). From work with His2 (the first pleolipovirus isolated) we know that the genome ends have proteins attached, and the His2 genome can be transfected into host cells to recover infectious virus (Porter and Dyall-Smith, 2008). It is a pity that more genetic investigations have not been pursued on viruses of this group.