Bacterial distribution in long-term dioxin-contaminated soil in Vietnam and novel dioxin degrading bacteria isolated from Phu Cat airbase

Herbicide-/dioxin-contaminated contamination in Vietnam is an environmental issue nowadays, despite Agent Orange being sprayed a long time ago. High levels of dioxin in military airbases cause hot spots of dioxin contamination sites in which potential biological source of microorganisms has developed. Understanding microorganism structure in contaminated soil is crucial for the bioremediation of the sites. Illumina Miseq platform was applied to sequence V3-V4 amplicons of long-term contaminated communities to evaluate the bacterial distribution. Contaminated soil from different regions Bien Hoa and Phu Cat showed a low level of connectedness; the species richness of Bien Hoa was much higher than that of Phu Cat. However, they shared similarities in the most abundant bacterial phyla: Actinobacteriota, Chloroflexi, Proteobacteria, Acidobacteriota, and Planctomycetota. Several xenobiotic-degrading genera were found, such as <i>Terrabacter, Nocardioides</i>, and <i>Streptomyces</i> of Actinobacteriota; <i>Bacillus</i>, <i>Paenibacillus</i>, and <i>Clostridium</i> of Firmicutes; <i>Burkholderia</i>, <i>Sphingomonas</i>, <i>Pseudomonas</i> and <i>Klebsiella</i> of Proteobacteria. Seven bacterial isolates grew on dioxin-containing medium belonging to Firmicutes, they were classified in order Bacillales, in which two strains belong to Paenibacillaceae, and the rests are in Bacillaceae. Two isolates removed more than 80% of total toxicity (mainly 2,3,7,8-Tetrachlorodibenzo-p-dioxin); strain PC5 is the first dioxin-degrading bacterium recognized in the genus <i>Neobacillus</i>.