Bacterial diversity losses: A potential extracellular driving mechanism involving the molecular ecological function of hydrophobic polycyclic aromatic hydrocarbons

The DNA transformation is vital to the horizontal gene transfer (HGT). The low-efficiency transformation of bare plasmid exposed to hydrophobic polycyclic aromatic hydrocarbons (PAHs) decreases the gene transfer level, and is possibly related to the loss of bacterial diversity at present. PAHs have great affinity for bare DNA through dispersion force and π-π overlap between PAHs and bases. These noncovalent interactions between PAHs and bases reduced the transformational efficiency of plasmid into bacterial recipients. Meanwhile these low-efficiency transformations for plasmid are controlled by the ions like Ca²⁺ in environment, in turn, presence of 0.5 mmol L^-1 Ca²⁺ recovered the efficiency from 3.2 (phenanthrene), 3.5 (pyrene) to about 4.45 and 4.75, respectively. The combination of Ca²⁺ with the -POO^-- groups in DNA forms strong electrovalent bonds, weakening the molecular effect of DNA on PAHs and in turn promoting the gene transfer exposed to PAHs.