MICROBIAL DIVERSITY IN A HYDROCARBON-CONTAMINATED AND CHLORINATED-SOLVENT-CONTAMINATED AQUIFER UNDERGOING INTRINSIC BIOREMEDIATION

A culture independent molecular phylogenetic approach was used to surv ey constituents of microbial communities associated with an aquifer co ntaminated with hydrocarbons (mainly jet fuel) and chlorinated solvent s undergoing intrinsic bioremediation. Samples were obtained from thre e redox zones: methanogenic, methanogenic-sulfate reducing, and iron o r sulfate reducing, Small-subunit rRNA genes were amplified directly f rom aquifer material DNA by PCR with universally conserved or Bacteria - or Archaea-specific primers and were cloned. A total of 812 clones w ere screened by restriction fragment length polymorphisms (RFLP), appr oximately 50% of which were unique. All RFLP types that occurred more than once in the libraries, as well as many of the unique types, were sequenced. A total of 104 (94 bacterial and 10 archaeal) sequence type s were determined. Of the 94 bacterial sequence types, 10 have no phyl ogenetic association with known taxonomic divisions and are phylogenet ically grouped in six novel division level groups (candidate divisions WS1 to WS6); 21 belong to four recently described candidate divisions with no cultivated representatives (OP5, OP8, OP10, and OP11); and 63 are phylogenetically associated with 10 well-recognized divisions. Th e physiology of two particularly abundant sequence types obtained from the methanogenic zone could be inferred from their phylogenetic assoc iation with groups of microorganisms with a consistent phenotype, One of these sequence types is associated with the genus Syntrophus; Syntr ophus spp, produce energy from the anaerobic oxidation of organic acid s, with the production of acetate and hydrogen. The organism represent ed by the other sequence type is closely related to Methanosaeta spp., which are known to be capable of energy generation only through aceti clastic methanogenesis. We hypothesize, therefore, that the terminal s tep of hydrocarbon degradation in the methanogenic zone of the aquifer is aceticlastic methanogenesis and that the microorganisms represente d by these two sequence types occur in syntrophic association.