Formatted Title

Spatial and Temporal Variation in the Microbial Community of Petroleum-Polluted Sediment across the Eastern Mediterranean Shoreline

Background/Objectives

The increased recent interest in oil and gas exploration and extraction along the eastern shore of the Mediterranean basin has raised concerns over the potential occurrence of spills and their associated long-lasting damage to marine ecosystems. It is well known that one of the most highly diverse ecosystems occur along shorelines across the world. The Mediterranean basin is especially notable for being a biodiversity hotspot, especially along its shores, with many endemic and native species belonging to its unique ecosystems. Such an ecological significance of the Mediterranean basin stresses the importance of prompt and effective oil spill response to minimize damage and protect natural resources. Bioremediation constitutes an alternative oil cleanup technique that is safer for the environment, relying on the ability of naturally occurring microbial populations to degrade petroleum hydrocarbon pollutants. Those hydrocarbon degraders form a highly dynamic and diverse sediment microbial ecosystem that can, in many cases, efficiently eliminate the pollution. Hence, understanding the structure and dynamics of indigenous marine microbial communities at contaminated sites is essential for successful execution of bioremediation strategies.

Approach/Activities

The coast of Lebanon that extends over 225 km on the eastern side of the Mediterranean basin was analyzed for the dynamic changes in sediment microbial communities in response to petroleum hydrocarbon pollution. Sediment samples were collected along the shores of Lebanon from 11 different sites at two distinct points in time: first in year 2017 and then in year 2021 following a major oil spill in summer 2021 polluting the Lebanese shores with tar balls. Illumina MiSeq technology was used to sequence the microbial 16S rRNA gene, and DADA2 pipeline was employed as an open-source software package for processing sequencing data using high-resolution sample inference. The DADA2 pipeline uses the Amplicon Sequence Variants approach instead of the traditional Operational Taxonomic Units clustering approach, providing a more precise identification of microbes and a more detailed picture of the diversity within a sample. Sediment microbial communities were correlated to measured levels of total petroleum hydrocarbons (TPHs), and were analyzed to better understand the long-term dynamics of microbial sediments in response to continuous and emerging sources of contamination affecting pollution type and levels.

Results/Lessons Learned

Results of the study show a significant diversity of microbial populations along the Lebanese shore, and a significant change in the sediment microbial structure within four years. Namely, Woeseia, Blastopirellula, and Muriicola were identified in sediment samples collected in year 2017, while a higher microbial diversity was observed in 2021 with Woeseia, Halogranum, Bacillus, and Vibrio prevailing in beach sediments. In addition, the results demonstrate a significant correlation between certain hydrocarbon degraders, such as Marinobacter and Vibrio, and measured hydrocarbon contamination levels. The findings highlight the dynamic nature of the microbial communities of the shore of Lebanon in response to variations in environmental conditions, namely the level and type of aquatic pollution.