Biodegradation potential of residue generated during the in-situ burning of oil in the marine environment.

The biodegradability of residues derived from in-situ burning, an oil spill response strategy which involves burning an oil slick on the sea surface, has not yet been fully studied. With a growing risk of oil spills, the fate of the persistent burn residue containing potentially toxic substances must be better understood. Microcosms were used to study the microbial community response and potential biodegradability of in-situ burn residues generated from Ultra Low Sulphur (ULS) marine diesel. Microcosm studies were conducted using residues originating from the burning of unweathered and weathered diesel, with the addition of a fertilizer and a dispersant. Burn residues were incubated for 6 weeks at 7 °C in natural seawater with continual agitation in the dark. Samples were subsequently sacrificed for chemistry as well as 16S rRNA gene amplicon and shotgun metagenomic sequencing. Chemistry analyses revealed a reduction in hydrocarbon concentrations. Medium chain-length n-alkanes (nC16-nC24) decreased by 8% in unweathered burn residue microcosms and up to 26% in weathered burn residue microcosms. A significant decrease in polycyclic aromatic hydrocarbon (PAH) concentrations was observed only for naphthalene, fluorene and their alkylated homologs, in the microcosms amended with residue produced from burning weathered diesel. Decreases of 2-24%, were identified depending on the compound. Microcosms amended with burn residues had distinct microbial communities marked by an increase in relative abundance of putative hydrocarbon degraders as well as an increase of known hydrocarbon-degradation genes. These novel results suggest that if in-situ burning is performed on ULS marine diesel, some of the indigenous bacteria would respond to the newly available carbon source and some of the residual compounds would be biodegraded. Future studies involving longer incubation periods could give a better understanding of the fate of burn residues by shedding light on the potential biodegradability of the more recalcitrant residual compounds.

Genomic analysis of carbon monoxide utilization and butanol production by Clostridium carboxidivorans strain P7.

Increasing demand for the production of renewable fuels has recently generated a particular interest in microbial production of butanol. Anaerobic bacteria, such as Clostridium spp., can naturally convert carbohydrates into a variety of primary products, including alcohols like butanol. The genetics of microorganisms like Clostridium acetobutylicum have been well studied and their solvent-producing metabolic pathways characterized. In contrast, less is known about the genetics of Clostridium spp. capable of converting syngas or its individual components into solvents. In this study, the type of strain of a new solventogenic Clostridium species, C. carboxidivorans, was genetically characterized by genome sequencing. C. carboxidivorans strain P7(T) possessed a complete Wood-Ljungdahl pathway gene cluster, involving CO and CO(2) fixation and conversion to acetyl-CoA. Moreover, with the exception of an acetone production pathway, all the genetic determinants of canonical ABE metabolic pathways for acetate, butyrate, ethanol and butanol production were present in the P7(T) chromosome. The functionality of these pathways was also confirmed by growth of P7(T) on CO and production of CO(2) as well as volatile fatty acids (acetate and butyrate) and solvents (ethanol and butanol). P7(T) was also found to harbour a 19 Kbp plasmid, which did not include essential or butanol production related genes. This study has generated in depth knowledge of the P7(T) genome, which will be helpful in developing metabolic engineering strategies to improve C. carboxidivorans's natural capacity to produce potential biofuels from syngas.