PhD DISSERTATION DEFENSE: OSCAR RAMFELT – “ECOTYPIC DIFFERENTIATION WITHIN ABUNDANT MAGNIMARIBACTERALES MARINE BACTERIA”
Abstract: SAR86 is one of the most common groups of bacteria found in surface seawaters across the globe. Yet, more than 30 years after it was first discovered, scientists still know surprisingly little about how it functions or how it varies in different parts of the global ocean. Here, we explored how SAR86 has diversified both genetically and ecologically by examining its evolutionary history, its potential biological roles, and where different genotypes tend to live. In the first part of this research, I analyzed over 700 genome sequences from SAR86, including samples from major global studies and the first ever fully sequenced SAR86 microbial strain grown in a lab. The results showed that SAR86 is actually a broad group, recently renamed Magnimaribacterales, that is made up of four families, each with many smaller branches that are distributed differently across the world’s oceans. Interestingly, only a few of these branches appear to make up the majority of the group’s population. While the group as a whole can break down fatty acids for energy via beta-oxidation, some branches have additional abilities including the genetic machinery to degrade steroidal-like polycyclic ring-containing compounds, and the ability to perform alpha-oxidation. In the second part of this work, I used data from Kāneʻohe Bay located on the Windward side of the Hawaiian island of Oʻahu to study how different types of Magnimaribacterales partition across adjacent coastal or open-ocean environments. I found that specific genotypes of Magnimaribacterales are specialized for certain habitats. These specializations include differences in how they process sugars and produce certain components of their cell membranes. In the final section, I examined how these bacteria are distributed at different depths in the stratified water column of the North Pacific Ocean. Some groups live only in surface waters, while others thrive much deeper in the water column and appear to possess the genetic machinery to help them break down more complex and harder-to-digest organic compounds. Altogether, this research highlights how Magnimaribacterales has evolved into many specialized forms that are well-suited to particular planktonic marine environments, helping explain its success and widespread presence in the ocean.
Location: Zoom
Date & Time: Wednesday, July 2, 2025 at 9:00am HST
Connect via Zoom:
https://hawaii.zoom.us/j/81191868650
Meeting ID: 811 9186 8650
Passcode: sar86
