Understanding the genetic strategies of SAR11 bacteria, the ocean's most abundant, is crucial for maintaining ecological balance and adapting to climate change.
Researchers at the Miguel Hernández University of Elche (UMH) have discovered the genomic basis for the evolutionary success of SAR11 marine bacteria. The study, published in Microbiome, reveals that these bacteria combine a shared "genetic core" with small genomic islands, each harboring a single "flexible gene". This allows the population to dynamically respond to environmental changes.
The marine microbiome is vital for sustaining ecosystems and driving global biogeochemical cycles. SAR11, a clade (group) of free-living bacteria, dominates ocean surface waters, comprising 20-40% of all prokaryotic cells (cells without a nucleus).
According to Mario López Pérez, UMH researcher, limitations in recovering the full genetic richness of natural populations have hindered understanding of microbial evolution. The UMH Microbial Genomics and Evolution Group combined single-cell genomics and long-read metagenomics to reconstruct the genetic diversity of SAR11 in the Mediterranean Sea.
The study found that SAR11 bacteria share an almost identical genetic core, representing 81% of their genome. The remaining portion, the "flexible genome," is concentrated in small regions, often with a single gene.
Carmen Molina Pardines, UMH Ph.D. student, explains that these small variations are always in the same location and contain genes with similar functions, but in different versions. This genomic pattern favors the coexistence of multiple strains and minimizes direct competition.
This structure creates polyclonal populations, or groups of multiple genetic variants coexisting in the same environment. This preserves essential genes and maintains functional redundancy, safeguarding a broad genetic reservoir. This allows the population to rapidly adapt to environmental pressures.
José M. Haro Moreno, UMH researcher, notes that these results offer insight into the strategies that explain the ecological success of SAR11 in nutrient-poor marine environments. The study also demonstrates that third-generation metagenomics overcomes technical limitations in studying these microorganisms.
This research positions UMH as a leader in marine microbiome evolution research. Understanding the genomic strategies of SAR11 can help us better understand and protect our oceans.