Assessing the degradation efficacy of native PAH-degrading bacteria from aged, weathered soils in an Australian former gasworks site

Abstract

The large-scale degradation of polycyclic aromatic hydrocarbons (PAHs) by bacteria represents a promising soil remediation strategy. The aim of this study was to identify bacterial isolates for potential use in the remediation of PAH-contaminated sites using selective isolation plating, Biolog™ MT2 evaluation and metabolic profiling on the Biolog™ system. Thirty-five bacterial isolates were isolated from aged, weathered PAH-contaminated soil using Bushnell Hass medium amended with phenanthrene as the sole carbon source. Selected isolates that were then able to grow on at least one of three model PAHs (naphthalene, phenanthrene and pyrene) were identified and then screened for their potential application in the bioremediation of aged, weathered soils from a former gasworks site based on Biolog™ MT2 data. The 16S rRNA gene sequencing showed that hydrocarbon degrading isolates were affiliated to Rhodococcus sp., Achromobacter sp., Oerskovia paurometabola, Pantoea sp., Sejongia sp., Microbacterium maritypicum and Arthrobacter equi. Enzyme studies confirmed catechol 1,2-dioxygenase activity in all of the isolates. Biolog™ Eco plates, applied in this study to evaluate the metabolic properties of seven isolates showed that all of these isolates could use a wide range of organic substrates, Sejongia sp. being the highest (28 of 31 substrates). Furthermore, the metabolic patterns of seven isolates on different substrates were summarized according to the biochemical categories of the substrates present on Biolog™ Eco plates. The isolates showed diverse performance on different biochemical categories (amino acids, phenolic compounds, amines, carbohydrates, carboxylic acids and polymers). An insight into the mechanisms by which selected bacteria degrade model PAHs and survive in nitrogen deficient soils was obtained. This study demonstrates the functional potential of indigenous bacteria for model PAHs-degradation and bioremediation of aged, weathered PAH contaminated sites of Australia.