According to Koutsovoulos et al., the waterbear gets along with about 23,031 protein-coding genes, and a total nuclear DNA payload of about 130 Mb. Though there is effort required to avoid contamination from bacterial DNA, as can easily happen when you are putting a microscopic organism with exactly 1034 cells into the blender to extract its chromosomes.
Tardigrades are meiofaunal ecdysozoans and are key to understanding the origins of Arthropoda. We present the genome of the tardigrade Hypsibius dujardini, assembled from Illumina paired and mate-pair data. While the raw data indicated extensive contamination with bacteria, presumably from the gut or surface of the animals, careful cleaning generated a clean tardigrade dataset for assembly.BUT another team of researchers reckon that all the bacterial DNA is not an artefact, but a functioning part of the 250-Mb tardigrade genome, as the species is prone to pilfering genetic material from other species:
Genome sequencing, direct confirmation of physical linkage, and phylogenetic analysis revealed that a large fraction of the H. dujardini genome is derived from diverse bacteria as well as plants, fungi, and Archaea.This happens when they recover from desiccation, is the theory (or from vacuum, or cryogenic temperatures, or electron-beam-bombardment in an electron microscope, or any of the other inconveniences that are part of the tardigrade life-cycle). When the DNA strands in their little tardigrade cells are all fragmented and damaged and need to be reassembled by madly-skilled rad51 error-correction enzymes, and the bacterial / Achaean DNA get caught up in the wash.
Obviously we are hoping that Boothby et al. are correct, as gene-hoovering tardigrades are far more likely to become shape-shifting body-melting all-devouring Thing-like monsters when they fall back to Earth after exposure to vacuum and radiation aboard a Soviet research satellite.
H/t P.Z. Myers