Insights into Mobile Genetic Elements of the Biocide-Degrading Bacterium HBP-1.

The sewage sludge isolate HBP-1 was the first bacterium known to completely degrade the fungicide 2-hydroxybiphenyl. PacBio and Illumina whole-genome sequencing revealed three circular DNA replicons: a chromosome and two plasmids. Plasmids were shown to code for putative adaptive functions such as heavy metal resistance, but with unclarified ability for self-transfer. About one-tenth of strain HBP-1's chromosomal genes are likely of recent horizontal influx, being part of genomic islands, prophages and integrative and conjugative elements (ICEs). carries two large ICEs with different functional specialization, but with homologous core structures to the well-known ICE of B13. The variable regions of ICE1 (96 kb) code for, among others, heavy metal resistances and formaldehyde detoxification, whereas those of ICE2 (171 kb) encodes complete -cleavage pathways for catabolism of 2-hydroxybiphenyl and salicylate, a protocatechuate pathway and peripheral enzymes for 4-hydroxybenzoate, ferulate, vanillin and vanillate transformation. Both ICEs transferred at frequencies of 10-10 per HBP-1 donor into , where they integrated site specifically into -gene targets, as expected. Our study highlights the underlying determinants and mechanisms driving dissemination of adaptive properties allowing bacterial strains to cope with polluted environments.