Impacts of bioremediation strategy on the activity and diversity of hydrocarbonoclastic bacteria in a petrogenic contaminated aquatic system
Creators: name: Sheppard, Petra
Publisher: name: RMIT University
Year: 2024

description: Current methods for removing weathered oil are heavily reliant on chemical dispersants and physical removal. These methodologies pose problems as rarely is all the oil removed without further disruption to the ecosystem or the addition of further chemical treatments. This study investigated the diversity of the hydrocarbonoclastic community naturally present on weathered crude oil and its potential to degrade hydrocarbons in marine environments, through the use of seawater mesocosms (200 ml). Examination of the native seawater community's capabilities of utilizing hydrocarbons as their sole carbon source identified a maximum recovery of just 6.6 x 101 CFU/ml, with these values dramatically increased in the weathered oil, reaching 4.1 x 104 CFU/ml. Having identified that a significant hydrocarbonoclastic community was available, replicate seawater mesocosms were used to follow the natural degradation of weathered crude oil over an 8 week period bioremediation strategy. By day 56, the natural inoculums degraded the soluble hydrocarbons to below detectable levels and biodegradation of the residual oil reached 66%. The natural crude oil community showed it was a valuable resource for bioremediation of pollutant environments. <br><br>Having established natural attenuation as a treatment method in small scale weathered crude oil degradation, enhanced bioremediation treatment methods were developed. To date, limited studies have focused on the development of a sustainable method of marine oil removal using a microbial community attached to a carrier. In this study, we used a tank mesocosm system (50 l) to follow the degradation of weathered oil (10 g l-1) using a bacterial consortium mobilised onto different carrier materials (alginate or shell grit). GCMS analysis demonstrated that the extent of hydrocarbon degradation was dependent upon the carrier material. Augmentation of shell grit with nutrients and exogenous hydrocarbon degraders resulted in 75 (± 14) % removal of &gt;C32 hydrocarbons after 12 weeks compared to 20 (± 14) % for the alginate carrier and 20 (± 1.42) % for the seawater control. Therefore, the shell grit carrier material was selected as the optimal remediation system further assessed in a pilot scale bioremediation study. The pilot scale application (5000 l) examined the ability of the augmented shell carrier material to degrade weathered crude oil (10 g l-1) in a marine simulated environment and assessed ecotoxicity impacts associated with the introduction and biodegradation of oil. Total petroleum hydrocarbon degradation was effectively reduced by 53 (± 5.75) % within 27 weeks. <br><br>16S rRNA sequence analysis was used to identify species present during the bioremediation process. In this study, we used stable isotope probing (SIP) to monitored the utilization rate of unlabeled (12C) and labeled (13C) substrates, benzene (0.559 μl l-1 h-1) and hexadecane (0.330 μl l-1 h-1) in pre-exposed seawater over 72 h. Microbial community analysis by RNA-SIP DGGE showed substantial differences between the banding pattern of 12C and 13C communities. Phylogenetic analysis of 16S rRNA gene sequences revealed the presence of known hydrocarbon degraders including Alcanivorax, Acinetobacter, Pseudomonas and Roseobacter. This research proved SIP to be a potentially useful tool for assessing the bioremediation potential in contaminated marine ecosystems. <br>