Hydrocarbon-degrading micro-organisms were obtained from mangrove sediments adjacent to Cocoa Creek on Cape Cleveland, Queensland. The area is a National Park with no known history of oil contamination. Separate sediment samples were collected from among the roots of the mangroves, Rhizophora stylosa and Avicennia marina, and the Holosarcia salt marsh. In the laboratory, sediments were added to Bushnell-Haas (BH) growth medium (Difco) and Gippsland Crude oil was added to stimulate the growth of hydrocarbon degraders. The flasks were incubated for 72 hours and the concentration of bacteria in the flasks containing the three sediment types, were sampled and the total numbers of bacteria estimated using a Neubauer haemocytometer. In the first series of flask experiments a medium range, preweathered crude oil (Gippsland Crude from the Bass Strait Basin) and micro-organisms isolated from Rhizophora mangrove sediments were used. To test whether mangrove pore water affected the rate of degradation, the oil and micro-organisms were incubated in BH growth medium made up with pore water instead of seawater. A chemical method of adding oxygen was tested by adding (MgO2) to flasks containing oil and micro-organisms in BH growth medium made up with seawater. A series of controls were also run.The relative efficiency of the micro-organisms isolated from the tropical mangrove and salt marsh habitats, was tested using preweathered Gippsland Crude, Arabian Light Crude and Bunker C oils. Flask experiments were conducted with nitrogen bubbled controls and time zero controls. The following analyses were conducted: Total Extractable Organic Matter (EOM) determined gravimetrically; Total oil determined by UV Fluorescence analysis (UVF); Total Hydrocarbons determined by gas chromatography with flame ionisation detection (GC-FID); The percentage of unresolved hydrocarbons (% UCM); Concentrations of individual isoprenoid and n-alkanes (µg/g dry weight); Ratios of isoprenoid to n-alkanes as biodegradation indices; Quantification of 218 individual aromatic and alkyl substituted aromatic hydrocarbons (PAH) over the biphenyl/naphthalene, fluorene, dibenzothiophene, phenanthrene/anthracene, benzanthracene/chrysene and pyrene through benzopyrene series determined by selected ion monitoring-gas chromatography/mass spectroscopy (SIM-GC/MS); Ratios of specific alkyl phenanthrene isomers to illustrate selective biodegradation; Sum of triterpine biomarkers in the hopane series as determined by SIM-GC/MS using m/z 191; selected sterane and potential demethylated hopane biomarkers as determined by SIM-GC/MS using m/z 217 and m/z 177; and Ratios of specific biomarkers useful as biodegradation indices.
A series of experiments were designed to provide information to assist in the formulation of a bioremediation strategy to treat oiled sediments in mangrove and salt marsh habitats in Queensland. The possible presence of inhibitors in pore water and low levels of molecular oxygen have been suggested as potentially limiting factors in oil degradation in mangrove mud.The first experiments tested the effects of mangrove pore water on degradation rates and also compared the degradation of oil under oxic and anoxic conditions, in the presence of micro-organisms isolated from mangrove sediments. Another set of experiments were designed to determine the rate at which hydrocarbon-degrading microorganisms from different intertidal habitats were able to degrade oil from different sources.
