Microbial responses to Cadmium and Oil pollution in Gulf of Guinea

Crude oil and cadmium (Cd) are prevalent pollutants in coastal systems in the Gulf of Guinea. We tested the toxic effects of crude oil (2mL L-1), Cd (4.4 µg L-) and the combined effect (Cd+Oil) on functional groups of the coastal microbial community through experimental incubation over time (6 days). Water for the experiment was collected from an artisanal fishing vessel 2 km south of the city of Cape Coast, Ghana (05°05.367', -001°15.019'). The experiment was carried out for 6 days from 29 Oct to 6 Nov 2019. Within 4hr after water collection, 12 glass aquarium bowls (mesocosms) were filled to 15 L by gentle syphoning the water from the sampling canisters, using silicone tubing. To homogenice starting conditions the water from the six canisters were distributed evenly between the mesocosms using stacked filling. The mesocosms were set up in a temperature-controlled room with continuous logging of room temperature by Hobo temperature loggers (23.6 ± 0.3 °C). Aquarium pumps and glass tubing were used to create continuous circulation in the bowls by gently bubbling air to each mesocosm and were exposed to a 12-hr photoperiod from white-fluorescence bulbs ca. 1m above the mesocosms providing 50-150 µmol photons m-2 s-1 depending on the ambient light from 2 windows. Samples for DNA were taken from the in situ water used for the incubations, and from all 12 replicates at the start (Day0), mid (Day3) and end (Day6) of the experiment. Sub-samples of 150 mL from all the mesocosms were filtered onto a 0.22 µm Durapore® Membrane Filter (Ø 47mm, Merck-Millipore), transferred into 2 mL cryotubes and stored at -30 °C until analysis. DNA was extracted from the filters using the DNeasy PowerSoil Kit (Qiagen) and sequenced for prokaryotic and eukaryotic community composition using the Illumina sequencing platform.