The bovine alveolar macrophage (bAM) DNA methylome is resilient to infection with Mycobacterium bovis

Whole genome bisulfite sequencing (WGBS) was used to assess the effect of M. bovis infection on the bAM DNA methylome (5-methylcytosine). The methylomes of bAM infected with M. bovis (n = 8) were compared to those of non-infected control bAM (n = 8) at 24 hours post-infection (hpi). No differences in DNA methylation (CpG or non-CpG) were observed between control and infected bAM. Analysis of DNA methylation at proximal promoter regions uncovered >250 genes harbouring intermediately methylated (IM) promoters (average methylation = 33–66%). Gene ontology (GO) analysis, focusing on genes with low, intermediate or highly methylated promoters, revealed that genes with IM promoters were enriched for immune-related GO categories; this enrichment was not observed for genes in the high or low methylation groups. Targeted analysis of two non-imprinted genes in the IM category, C1QB and IL2RA, confirmed the WGBS observation. This study is the first in cattle to examine genome-wide DNA methylation at single nucleotide resolution in an important bovine cellular host-pathogen interaction model and provides evidence for intermediate promoter methylation in bAM. Examination of CpG methylation in control and Mycobacterium bovis infected bovine macrophages, 24 hours post infection