Award: OCE-2149128

Intellectual merit. Marine bacteria are among the most abundant organisms on Earth and play essential roles in shaping ocean ecosystems and global biogeochemical cycles, including the transformation of carbon and nutrients that support marine food webs. Although the ocean contains immense microbial diversity, a relatively small number of bacterial groups dominate surface waters worldwide, making them critical targets for understanding how ocean systems function. This project focused on one such group, known as SAR86 (recently renamed the bacterial order Magnimaribacterales), which is consistently abundant across the global ocean but has historically been difficult to study due to a lack of laboratory cultures. By integrating laboratory experiments, genome-resolved analyses, and long-term ocean observations across a coastal-to-open ocean environmental gradient in the tropical Pacific Ocean, this work addressed fundamental questions about how genetic diversity within this dominant microbial group is generated, structured, and maintained in nature. Using the complete genome of the first cultivated SAR86 strain (Magnimaribacter mokuoloeensis strain HIMB1674) as a reference, we linked genomic variation to environmental patterns observed from Kāneʻohe Bay, a well-studied coastal model system, to Station ALOHA in the North Pacific subtropical gyre. These analyses revealed that even highly abundant microbial groups are composed of distinct ecological types adapted to specific environmental conditions, including differences across water depth and nutrient availability. Together, these findings establish a foundation for understanding the ecological and evolutionary roles of dominant marine bacteria at a global scale.

Broader impacts. This project generated lasting resources that extend beyond its scientific findings. We developed a comprehensive database of SAR86 genetic sequences and a suite of molecular probes that enable direct detection and quantification of these bacteria in environmental samples, supporting future studies of marine microbial communities. The genome of strain HIMB1674 has been made publicly available, providing a valuable reference for researchers worldwide. The project supported the training and professional development of graduate students, postdoctoral researchers, and undergraduate students, integrating participants into all aspects of the research, including field sampling, laboratory experimentation, and computational analysis. One graduate student completed a Ph.D. based on this work, while others continue to build on these findings. In addition, the project contributed to broadening participation in ocean sciences by supporting undergraduate students from Hawaiʻi, including individuals of Native Hawaiian and Pacific Islander ancestry, in hands-on research experiences. Together, these outcomes advance fundamental understanding of microbial life in the ocean, provide new tools and data for the scientific community, and help train a diverse next generation of scientists working at the intersection of biology, evolution, and oceanography.

Last Modified: 04/18/2026
Modified by: Michael S Rappe