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Bacterial dynamics and abundance; quantitative coupling of hydrocarbon degradation and specific bacterial communities

Final Activity Report Summary - BACTOIL (Bacterial dynamics and abundance; quantitative coupling of hydrocarbon degradation and specific bacterial communities)

Crude oil hydrocarbon degrading bacteria are ubiquitous in the environment, yet spilled oil is rarely degraded rapidly. This is because a major factor controlling the fate of crude oil released to the environment is the availability of inorganic nutrients which are required to provide the hydrocarbon-degrading bacteria with a balanced diet, allowing them to grow on the hydrocarbons, which are rich in carbon but lack the nitrogen and phosphorous that the organisms need to produce biomass. Inorganic nutrient treatment can therefore be an effective way to enhance the degradation of spilled oil. However, the effects of nutrient addition on growth of hydrocarbon-degrading bacteria and oil degradation are not systematically understood and this information is important in determining the optimum amount of nutrients to achieve cleanup of an oil contaminated site. To address this, the BACTOIL project investigated the quantitative and qualitative effects of inorganic nutrient treatments on the degradation of spilled oil on marine beach sediments.

The performed work demonstrated that inorganic nutrient treatment of oil-contaminated beach sediment led to a rapid selection for bacteria of the genus alcanivorax and that the rate of hydrocarbon degradation and growth of alcanivorax was directly related to the amount of added inorganic nutrients. Within a five day period alcanivorax increased in numbers by 10 to 1 000 times. Furthermore, it was apparent that growth yields of alcanivorax decreased with time, indicating that, after initial stimulation of the population of hydrocarbon-degrading bacteria, the continuous amendment with nutrients at a lower concentration would sustain hydrocarbon degradation.

It was also determined in these experiments that the primary limiting inorganic nutrient was nitrate rather than phosphate. In addition, at low nutrient concentrations, there was a strong selection for aromatic hydrocarbon-degrading bacteria of the genus cycloclasticus that were outcompeted by alcanivorax, which degraded saturated hydrocarbons at higher nutrient concentrations. This provided a possible means to manipulate the degradation of crude oil so as to favour the degradation of the more toxic aromatic oil components, initially followed by degradation of the more abundant aliphatic oil components.