Effect of model sorptive phases on phenanthrene biodegradation: Different enrichment conditions influence bioavailability and selection of phenanthrene-degrading isolates

The sorption of organic contaminants by natural organic matter (NOM) often limits substrate bioavailability and is an important factor affecting micro bial degradation rates in soils and sediments. We hypothesized that reduced substrate bioavailability might influence which microbial assemblages are responsible for contaminant degradation under enrichment culture conditions . Our primary goal was to characterize enrichments in which different model organic solid phases were used to establish a range of phenanthrene bioava ilabilities for soil microorganisms, Phenanthrene sorption coefficients (ex pressed as log K-D values) ranged from 3.0 liters kg(-1) for Amberlite carb oxylic acid cation-exchange resin (AMB) to 3.5 liters kg(-1) for Biobeads p olyacrylic resin (SM7) and 4.2 liters kg(-1) for Biobeads divinyl benzene r esin (SM2), Enrichment cultures were established for control (no sorptive p hase), sand, AMB, SM7, and SM2 treatments by using two contaminated soils ( from Dover, Ohio, and Libby, Mont,) as the initial inocula, The effects of sorption by model phases on the degradation of phenanthrene were evaluated for numerous transfers in order to obtain stable microbial assemblages repr esentative of sorptive and nonsorptive enrichment cultures and to eliminate the effects of the NOM present in the initial inoculum. Phenanthrene degra dation rates were similar for each soil inoculum and ranged from 4 to 5 mu mol day(-1) for control and sand treatments to approximately 0.4 ymol day(- 1) in the presence of the SM7 sorptive phase. The rates of phenanthrene deg radation in the highly sorptive SM2 enrichment culture were insignificant; consequently, stable microbial populations could not be obtained. Bacterial isolates obtained from serial dilutions of enrichment culture samples exhi bited significant differences in rates of phenanthrene degradation performe d in the presence of SM7, suggesting that enrichments performed in the pres ence of a sorptive phase selected for different microbial assemblages than control treatments containing solid phase phenanthrene.