Relationships between microbial populations and phenanthrene biodegradation in soil

Strongly sorbed pollutants impact soil microbial community composition and biodegradation kinetics directly, through toxicity or use as carbon sources, or indirectly via the solvents added with the pollutants. Goals of this research were to: (1) quantify the bioavailability of phenanthrene to phenanthrene-degrading microorganisms in soil; (2) develop and apply molecular methods to measure phenanthrene effects on microbial populations and community composition; (3) determine the effect of various solvents, used to dissolve phenanthrene, on soil communities.; Bioavailability of phenanthrene to a phenanthrene-degrading Arthrobacter sp., strain RP17, inoculated into soil, declined in a biphasic pattern. Changes in bioavailability were more similar to availability of phenanthrene as measured using hexane/water than methanol extraction. Despite the decline in bioavailability, additional phenanthrene could be mineralized with subsequent inoculations with freshly cultured cells. Bioaugmentation of sorbed pollutants in soil may be improved through use of multiple inoculations.; The population density of strain RP17 was quantified in soil with a competitive quantitative polymerase chain reaction method. The bacterium multiplied 35-fold in a non-sterile soil amended with 500$m$g/g phenanthrene.; Intergenic Transcribed Spacer (ITS) analysis of DNA extracted from the soil community indicated only one bacterial population grew in Tinker soil after amendment with 250$m$g/g phenanthrene. Sequences of the new fragments that appeared in the ITS patterns suggested the bacterium was an actinomycete, closely related to the genus Streptomyces.; Solvents used to add phenanthrene to soil substantially impacted phenanthrene mineralization kinetics and soil community composition. Use of greater than 5$m$l/g methylene chloride decreased mineralization rates and changed the community phospholipid fatty acid (PLFA) profiles, suggesting the solvent was toxic to the microbial community. Both ITS and PLFA analysis suggest the solvent methanol, which appeared to be used as a carbon source, changed the community composition substantially more than did methylene chloride or hexane.; In conclusion, phenanthrene biodegradation kinetics in soil corresponded strongly to temporal changes in phenanthrene bioavailability. Molecular fingerprinting methods indicated that biodegradation of phenanthrene was associated with enrichment of very few bacterial populations in soils. Microbial community composition may be altered more by the addition of carrier solvents, such as methanol, than by addition of phenanthrene.