ORIGINAL PAPER Comparison of indigenous and exogenous microbial populations during slurry phase biodegradation of long-term hydrocarbon-contaminated soil Arturo Aburto-Medina • Eric M. Adetutu • Sam Aleer • John Weber • Sayali S. Patil • Petra J. Sheppard • Andrew S. Ball • Albert L. Juhasz Received: 9 April 2012 / Accepted: 29 May 2012 / Published online: 10 June 2012 Ó Springer Science+Business Media B.V. 2012 Abstract In this study, a number of slurry-phase strategies were trialled over a 42 day period in order to determine the efficacy of bioremediation for long-term hydrocarbon-contaminated soil (145 g kg -1 C 10 – C 40 ). The addition of activated sludge and nutrients to slurries (bioaugmentation) resulted in enhanced hydrocarbon removal (51.6 ± 8.5 %) compared to treatments receiving only nutrients (enhanced natural attenuation [ENA]; 41.3 ± 6.4 %) or no amendments (natural attenuation; no significant hydrocarbon removal, P \ 0.01). This data suggests that the microbial community in the activated sludge inoculum contributed to the enhanced removal of hydrocarbons in ENA slurries. Microbial diversity in slurries was monitored using DGGE with dominant bands excised and sequenced for identification. Applying the differ- ent bioremediation strategies resulted in the formation of four distinct community clusters associated with the activated sludge (inoculum), bioaugmentation strat- egy at day 0, bioaugmentation strategy at weeks 2–6 and slurries with autoclaved sludge and nutrient additions (bioaugmentation negative control). While hydrocarbon-degrading bacteria genera (e.g. Aqua- bacterium and Haliscomenobacter) were associated with the hydrocarbon-contaminated soil, bioaugmen- tation of soil slurries with activated sludge resulted in the introduction of bacteria associated with hydrocar- bon degradation (Burkholderiales order and Klebsiella genera) which presumably contributed to the enhanced efficacy for this slurry strategy. Keywords Activated sludge  Bioaugmentation  Hydrocarbons  Slurry phase bioremediation Introduction The refining of oil as well as petrochemical manufac- turing has left a legacy of contamination in the form of hydrocarbon-contaminated soils and groundwater. The use of bioremediation, which relies on the metabolic potential of microorganisms for the degra- dation of contaminants in the environment, represents A. Aburto-Medina  E. M. Adetutu  S. S. Patil  P. J. Sheppard  A. S. Ball School of Biological Sciences, Flinders University of South Australia, Adelaide 5001, Australia A. Aburto-Medina  S. S. Patil  P. J. Sheppard  A. S. Ball School of Applied Sciences, Royal Melbourne Institute of Technology, Bundoora, VIC 3083, Australia S. Aleer  J. Weber  A. L. Juhasz (&) Centre for Environmental Risk Assessment and Remediation (CERAR), University of South Australia, Mawson Lakes Campus, Adelaide, SA 5095, Australia e-mail: albert.juhasz@unisa.edu.au S. Aleer  J. Weber  A. L. Juhasz Cooperative Research Centre for Contamination Assessment of the Environment (CRC CARE), Mawson Lakes, Adelaide, SA 5095, Australia 123 Biodegradation (2012) 23:813–822 DOI 10.1007/s10532-012-9563-8