The Impact of Highly Weathered Oil from the Most Extensive Oil Spill in Tropical Oceans (Brazil) on the Microbiome of the Coral Mussismilia harttii.

In 2019, the largest oil spill ever recorded in tropical oceans in terms of extent occurred in Brazil. The oil from the spill was collected directly from the environment and used in an exposure experiment with the endangered reef-building coral Mussismilia harttii. The treatments of the experiment were control (without oil), 1% oil, 2.5% oil, and direct contact of coral with oil. The most abundant hydrocarbon in the seawater of the experiment was phenatrene, which is toxic to corals. However, overall, the concentration of PAHs was not very high. The analysis of the maximum photosynthetic capacity of Symbiodiniaceae dinoflagellates showed a small impact of oil on corals, mainly on the contact treatment. However, coral microbiomes were affected in all oil treatments, with the contact treatment showing the most pronounced impact. A greater number and abundance of stress-indicating and potentially pathogenic bacteria were found in all oil treatments. Finally, this highly weathered oil that had lain in the ocean for a long time was carrying potentially coral-pathogenic bacteria within the Vibrionaceae family and was able to transmit some of these bacteria to corals. Bacteria within Vibrionaceae are the main causes of disease in different species of corals and other marine organisms.

The influence of the Doce River mouth on the microbiome of nearby coastal areas three years after the Fundão Dam failure, Brazil.

The failure of the Fundão Dam, considered the world's largest mining disaster, released more than 55 million m3 of ore tailings into the environment. The sediment plume formed by water and tailings spread along approximately 663 km of water bodies of the Doce River basin. It reached the Atlantic Ocean sixteen days after the dam failure. However, the effects of the dam failure in the marine coastal areas years after the disaster are still unknown. This study aims to evaluate water and sediment microbial communities of nearby coastal areas three years after the Fundão Dam failure, using 16S rRNA gene amplicon sequencing. A total of 441 samples from 25 locations were collected during two different seasons (dry and rainy). The results showed that the Doce River mouth seems to divide the microbial communities from the southern and northern stations into two groups. The plume of sediments from the Doce River seems to be impacting the marine microbiome even at the furthest sampling stations. Bacterial (Anaerolineaceae, Thermodesulfovibrionia and Rhodopirellula) and Archaeal (Bathyarchaeia and Woesearchaeia) taxa, found in high abundance in the sediment of the Doce River mouth, have been previously described in high abundance in heavy metal contaminated sediments, including the Doce River itself and in mine tailing sediments. Cyanobium, found in great abundance in the water samples from the Doce River mouth, was also reported as the most abundant in the water of the Doce River after the Fundão Dam failure. Overall, the farther from the Doce River mouth the sample was, the lower the relative abundances of these taxa were. These results provide strong evidence that the sediment plume released by the Fundão Dam failure is probably impacting the marine microbiome of nearby coastal areas, even three years after the dam failure.