16S rDNA-based characterization of BTX-catabolizing microbial associationsisolated from a South African sandy soil

In the presence of different selection pressures, particularly pH and elect ron donor concentration, indigenous microbial associations which catabolize selected petroleum hydrocarbon components (benzene, toluene and o-, m- and p-xylene (BTX)) were enriched and isolated from a petroleum hydrocarbon-co ntaminated KwaZulu-Natal sandy soil. Electron microscopy revealed that, num erically, rods constituted the majority of the populations responsible for BTX catabolism. Molecular techniques (polymerase chain reaction (PCR) and 1 6S rDNA fingerprinting by denaturing-gradient gel electrophoresis (DGGE)) w ere employed to explore the diversities and analyze the structures of the i solated microbial associations. Pearson product-moment correlation indicate d that the different, but chemically similar, petroleum hydrocarbon molecul es, effected the isolation of different associations. However, some similar numerically-dominant bands characterized the associations. A 30% similarit y was evident between the m- and o-xylene-catabolizing associations regardl ess of the molecule concentration and the enrichment pH. PCR-DGGE was also used to complement conventional culture-based microbiological procedures fo r environmental parameter optimization. Band pattern differences indicated profile variations of the isolated associations which possibly accounted fo r the growth rate changes recorded in response to pH and temperature pertur bations.