Genetic, epigenetic and microbiome characterisation of earthworm species and lineages along a radiation exposure gradient at Chernobyl

The effects of exposure to ionising radiation was assessed based on genetic, epigenetic and microbiome characteristics of the “hologenome” of earthworms collected at sites with different rates of exposure to ionising radiation within the Chernobyl exclusion zone (CEZ). Two earthworm species, A. caliginosa and O. lacteum were those most frequently found at the visited sites, however, only O. lacteum was present at sufficient numbers across different exposure levels to enable (?) comparative hologenome analysis. The identification of morphotype O. lacteum as a probable single clade was established using a combination of mitochondrial (cytochrome oxidase I) and nuclear genome (MSPI loci). No clear site associated differences in population genetic structure was found between populations using MSPI marker loci. No relationship between ionising radiation exposure levels and the percentage of methylated loci of pattern of distribution of DNA methylation marks was found for the sampled O. lacteum. Microbiome structure was clearly site dependent, with gut microbiome community structure and diversity being systematically associated with calculated site specific earthworm dose rates. However, there was also co-correlation between earthworm dose rates and other soil properties across the sites, notably pH, which is also known to affect soil bacterial community structure. Such co-correlation means that it is not possible to attribute microbiome changes unequivocally to radionuclide exposure. A better understanding of the relationship between radionuclide exposure and soil bacterial community response is, therefore, needed to establish whether long-term radiation exposure has influenced both soil and host associated microbial communities in radionuclide contaminated soils in the CEZ.