[16S rDNA-RFLP analysis of structure and diversity of an aerobic microbial community degrading hexachlorobenzene]

Hexachlorobenzene is a chlorinated aromatic hydrocarbon that was widely used as a seed dressing for prevention of fungal growth on crops, and is also a component of fireworks, ammunition, and synthetic rubbers. Because of the bioaccumulation and persistence of hexachlorobenzene as well as its potential toxicity, hexachlorobenzene must be removed from environment. The potential for aerobic dechlorination of hexachlorobenzene by a hexachlorobenzene-adapted mixed culture was investigated. An aerobic microbial community which was able to grow at the presence of hexachlorobenzene was enriched from sediment from contaminated site after incubating about 2 months. During the growth of the mixed microorganisms on hexachlorobenzene, the accumulating consumption of oxygen, the microbial population curve and the release of Cl- were investigated. The data suggest the rapid degradation of hexachlorobenzene to support microbial growth and the aerobic decholrination of hexachlorobenzene was observed. The result showed that the mixed microorganisms were able to utilize hexachlorobenzene as sole carbon and energy source. It was shown that up to 55% of HCB could be degraded during 18 days incubation at 30 degrees C in mineral salts medium (pH 7.0) with 4.5mg/L HCB. The calculated rate of hexachlorobenzene biodegradation was 137.5 microg/ (L x d). The 16S rDNA genes were amplified from community DNA by using primers specific to bacteria and were subsequently cloned. The cloned 16S rDNA fragments were reamplified, and restriction analysis was performed following separate digestion with enzymes Hae III and Rsa I. Application of restriction fragment length polymorphism screening approach revealed 9 clusters, and 3 major clusters were sequenced. Nearly complete 16S rDNA sequence analysis show that the microbial community was dominated by Alcaligenes and Azospirillum groups. This is the first report describing aerobic dechlorination of hexachlorobenzene via dehalorespiration by a microbial community which was enriched from contaminated site. The microbial community can be used to degrade highly recalcitrant chlorinated pollutants.