Structure of a natural microbial community in a nitroaromatic contaminatedgroundwater is altered during biodegradation of extrinsic, but not intrinsic substrates

This study demonstrates microbial community changes over time in a nitroaro matic-contaminated groundwater upon amendment with hydrocarbons previously unknown to the microbial community (extrinsic) and hydrocarbons previously known to the microbial community (intrinsic). Sealed flasks, shaken and inc ubated at 25 degrees C, containing contaminated groundwater and salts were amended twice with extrinsic hydrocarbons including phenol, benzoic acid, a nd naphthalene, and intrinsic hydrocarbons including 2,4-dinitrotoluene (2, 4-DNT) and para-nitrotoluene (p-NT). Microbial growth, biodegradation, and community structure changes measured by random amplified polymorphic DNA (R APD) and quantitative PCR (qPCR) targeting catechol-2,3-dioxygenase (C230) genes were monitored over time. All amended substrates were biodegraded aft er both substrate amendments except for 2,4-DNT, which was only partially d egraded after the second amendment. Unique microbial communities were devel oped in flasks amended with phenol, benzoic acid, and naphthalene. However, in the flasks amended with intrinsic hydrocarbons the microbial community remained similar to the unamended control flasks. The relative amount of C2 30 genes detected by qPCR correlated with the biodegradation of phenol and naphthalene but not with 2,4-DNT. The results showed that a selection for m icroorganisms capable of catabolizing extrinsic hydrocarbons naturally and initially present in the nitroaromatic-contaminated groundwater occurred. H owever, growth-linked biodegradation of added intrinsic hydrocarbons was no t selective.