The Bacillus cereus group includes genetically close bacteria with a wide variety of ecological niches, life cycles and hosts. Despite the high genome conservation, extra-chromosomal genetic material diverges between these species. Actually, the plasmid genes are responsible for their discriminative properties, especially toxin genes. For instance, the production of the dodecadepsipeptide cereulide, which is, is responsible for emetic syndrome in foodborne intoxication, requires the non-ribosomal peptide synthetase Ces encoded by the ces locus on the pCER270 megaplasmid. The 270 kb pCER270 shows 222 coding-sequences, with only 39% having an assigned function. To determine the role of pCER270 in strain adaptation, virulence and ecological niche specificity, we tagged pCER270 in the emetic reference strain F4810/72 with an antibiotic-resistance cassette using CRISPR/Cas9 technology, and transferred it to other B. cereus group members by conjugation. Since pCER270 is not conjugative by itself, we used a pXO16-derivative to mobilize its transfer. Transconjugants and their parental strains were subjected to Fourier Transformed Infrared (FTIR-) spectroscopy for metabolic fingerprinting The chemometric analysis of the respective FTIR spectra indicated specific metabolic traits linked to the presence of the mega-plasmid. Furthermore, we performed RNA sequencing experiments in the different strains to investigate gene regulations related to the presence of pCER270. Transcriptomic analysis suggested the existence of a strain specificity in chromosome-pCER270 transcriptional crosstalk. Moreover, we could observe that, despite a constant global expression level of pCER270 in all hosts, some specific loci were differentially regulated depending on the genomic context.