Hydrocarbon-degrading Alcanivorax found in plumes of hydrothermal vents

by Nirvan Marathe

These petrol-munching bacteria show immense ecological potential…

Left- Black smoker hydrothermal vent billows fluids into surrounding seawater at Niua volcano, Tonga (courtesy of United States Geological Survey). Right- Alcanivorax bacteria (courtesy of scientificamerican.com).

Now you might’ve heard of the bacterial genus Alcanivorax, some species within it were recruited to help BP clean their oil spill in the Gulf of Mexico back in 2010. Possessing the ability to degrade hydrocarbons, these revolutionary bacteria have been of great scientific interest in recent years. They were first seen blooming in oil-contaminated areas, and further research uncovered their extensive production of exopolysaccharides and pili, through which they adhere to the oil-water surface. The bacteria a complete set of genes for use in alkane degradation, coding for enzymes including alkane hydroxylases. Despite this immense potential, a thorough analysis of deep-sea dwelling Alcanivorax species was still lacking until a recent study.

Dr Dede’s team endeavoured to analyse the microbial composition of the plumes produced by hydrothermal vents (both black and white smokers) in the Niua, Niuatahi and Maka underwater volcanoes, located in the Tonga Arc. Hydrothermal vent fields across these sites were sampled

in an expedition by the deep ocean research vessel RV Sonne, in July 2018. The scientists extracted DNA from the samples and conducted 16S rRNA gene analysis, meta-omics sequencing and ASV analysis to identify representative 16S rRNA sequences for Alcanivorax. Catalysed reporter deposition-FISH was then performed with probes that targeted the Alcanivorax genus before metagenome analysis which identified 6 Alcanivorax affiliated metagenome-assembled genomes (MAGs). This allowed the team to undertake a phylogenetic tree reconstruction using the 16S rRNA sequences derived from the MAGs. Genes for key enzymes and pathways including carbon fixation, heavy-metal resistance and sulphate reduction were identified. Of particular interest were the genes encoding alkane monooxygenase, cytochrome P450 and alcohol dehydrogenase, all of which are key players in the degradation of short and medium length alkanes. Interestingly, the study revealed a dominance of two Alcanivorax species in the microbial population at the Niuatahi and Maka volcano sites, despite there being no data of hydrocarbon release from these sites- that being what typically leads to Alcanivorax blooming. This odd observation is coupled with the finding that the most Alcanivorax abundant samples were those from weaker plume signal. This led scientists to hypothesise that the bacteria’s growth was indicating the presence of a hydrocarbon, but not from the assessed vents. The result of seismic surveys revealed a potential source in Eocene rocks found in the area, or from high magmatic activity in the area causing potential seepage of hydrocarbon in the vicinity of the Niuatahi and Maka sites.

This study provided several examples of further application for bacteria in the intriguing Alcanivorax genus. These microbes are being currently and can be further used in the bioremediation of environments contaminated by petroleum oils. Furthermore, the study serves as evidence that high Alcanivorax abundance can act as an indicator for hydrocarbon leakage and ecosystem perturbation. Nonetheless, these nifty bacteria’s importance will without a doubt be on the increase, as scientists discover more and more about their capabilities.

Original paper: Dede B, Priest T, Bach W, Walter M, Amann R, Meyerdierks A. High abundance of hydrocarbon-degrading Alcanivorax in plumes of hydrothermally active volcanoes in the South Pacific Ocean. ISME J. 2023 Jan 31;1–11.

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