Cultures of the microbe Mycobacterium vanbaalenii strain PYR-1 can break down the carcinogenic polyaromatic hydrocarbon benz[a]anthracene, according to US researchers. The team used UV-Vis spectroscopy and high-performance liquid chromatography (HPLC) to determine how the PAH is degraded.

PYR-1 is considered to be one potential candidate for detoxifying chemical waste containing quantities of carcinogens, mutagens and teratogens, including benzanthracenes, pyrenes, and phenanthrenes. Bacteria are well known as actively degrading such compounds in aquatic and terrestrial environments. The end product is usually a metabolite that is more soluble in water than the parent and has lower biological activity and so reduced toxicity.

The microbial degradation of PAHs and other compounds could be preferable to burning such waste, which can release potentially toxic fumes into the environment. It could also provide a bioremediation solution to reclaiming contaminated brown-field and other sites. Simply reintroducing the indigenous microbes into sterile contaminated land could allow the site to be cleaned up with minimal cost or effort.

To be useful, biotechnologists would like to understand more precisely exactly how this microbe puts its enzymes to work to breakdown these materials into non-toxic forms.

Joanna Moody, James Freeman, and Carl Cerniglia of the Division of Microbiology, at the National Center for Toxicological Research, part of the US Food and Drug Administration (FDA) in Jefferson, Arkansas, grew PYR-1 grown in a mineral salts medium containing nutrients and the PAH benz[a]anthracene. They found that the microbe had metabolized about 15% of the PAH after just twelve days of incubation.

They extracted metabolites from the culture medium using neutral and acidic ethyl acetate characterized them from their HPLC, UV-vis, gas chromatography/mass (GC/MS) and nuclear magnetic resonance (NMR) analysis. Derivitisation by trimethylsilylation allowed them to identify each definitively using GC/MS. The results showed that the microbe initiates attack on benz[a]anthracene at its C-1,2-, C-5,6-, C-7,12- and C-10,11-positions and reduces the compound's toxic effects on the microbe by forming soluble dihydroxylated and methoxylated intermediates.
The microbe has already been trialled in field and bioreactor studies with application towards bioremediation, Cerniglia told us.

Related links:

• Biodegradation, 2005, 16, 513-526
• FDA National Center for Toxicological Research
• Cerniglia Page
• Freeman Page 

Article by David Bradley