Test of Polyaromatic Hydrocarbon Degradation by Nitrate-reducing Microorganisms Isolated from Tallgrass Prairie Soils

Abstract

Soils are frequently contaminated with hydrocarbons such as polyaromatic hydrocarbons (PAH). This contamination inhibits the growth of some microorganisms in the contaminated soils. However, the contamination may select for microorganisms capable of hydrocarbon degradation
under aerobic or anaerobic conditions. Forty five strains of bacteria isolated from tallgrass prairie soil samples were screened for the ability to grow with naphthalene as sole carbon source under aerobic
conditions by culturing on minimal medium containing naphthalene as the sole carbon source. Our results showed that none of the 45 strains were able to grow on naphthalene under these conditions.
Three out of the 45 strains, e.g. one strain each classified as Ensifer, Stenotrophomonas, or Serratia, were tested for the ability to degrade naphthalene under nitrate reducing conditions. All three strains
were facultative anaerobes and showed the physiology of nitrate or nitrate/nitrite reduction when grown under nitrate-reducing conditions in medium containing yeast extract. Two strains (e.g. Stenotrophomonas and Serratia) were tested for the ability to grow on naphthalene, gasoline, or
benzene under nitrate-reducing conditions. The Serratia grew poorly on the hydrocarbons, but Stenotrophomonas reached its highest O.D. values on naphthalene. However, upon re-testing a wellwashed cell suspension of the Stenotrophomonas, no loss of naphthalene was found when grown
under nitrate-reducing conditions. Although it might be expected that crude-oil contamination would select for PAH degraders, we did not find the nitrate reducing/nitrite reducing isolates to be capable of naphthalene-degradation under aerobic or nitrate-reducing conditions. ©2015 Oklahoma Academy of Science