Genomic Flexibility Powers Ocean’s Most Abundant Bacteria, UMH Study Finds.

Researchers at the Miguel Hernández University of Elche (UMH) have discovered how the ocean’s most abundant bacteria, SAR11, thrive and adapt in changing marine environments. The study, published in the journal Microbiome, uncovers how these microorganisms use compact genomic elements to respond flexibly to environmental shifts.

SAR11, a group of free-living marine bacteria, dominates surface ocean waters, accounting for up to 40% of all prokaryotic cells. Despite their global presence, past efforts to fully explore their genetic diversity have faced challenges due to limitations in available genomic technologies and difficulties in culturing these microbes.

Now, the UMH team, part of the university’s Department of Plant Production and Microbiology, has successfully applied third-generation metagenomics combined with single-cell genomics to reconstruct the genomes of SAR11 populations directly from environmental samples collected in the Mediterranean Sea.

Their findings show that SAR11 bacteria possess a highly conserved genetic core—making up approximately 81% of the genome—accompanied by small, variable regions called genomic islands. Each of these islands typically contains a single "flexible gene" that can differ between strains but generally performs similar functions. These variable genes are located in consistent positions across different bacterial strains, providing adaptability without compromising genetic stability.

“This genetic arrangement supports the coexistence of multiple strains within the same population and reduces direct competition,” said Carmen Molina Pardines, Ph.D. student and lead author of the study. These diverse strains form polyclonal populations, enabling rapid adaptation to environmental changes while preserving essential genetic functions.

According to co-primary author José M. Haro Moreno, this structure gives SAR11 a crucial advantage in nutrient-poor marine regions like the Mediterranean, helping maintain biodiversity and ecosystem resilience. The study also underscores how third-generation sequencing technologies are overcoming past obstacles in marine microbiology, particularly in understanding organisms that are difficult to culture in laboratory conditions.

Senior researcher Mario López Pérez emphasized that this integrative approach enhances our ability to link microbial evolution with ecological function. “Our findings not only deepen knowledge of SAR11’s genomic dynamics but also highlight the importance of microbial populations in regulating global ecological processes,” he said.

This groundbreaking work positions UMH as a leader in marine microbiome research, offering new insight into the mechanisms that support ocean life and its role in global environmental balance.

Source:https://phys.org/news/2025-05-tiny-genomic-islands-ocean-abundant.html

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