Decoding Microbial “Relationship Statuses” at OSM 2016

Abstract

Some of the ocean's smallest organisms were the stars of the “Microbial Interactions in Ocean Ecosystems: Ecology to Biochemistry” session at OSM, the focus of which was on the relationships between marine microbes. Tying together far-ranging topics such as toxic algal blooms and novel methods for detecting bacterial chemotaxis was the idea that these microscale interactions are not only highly specific but also ecologically important. We heard from many speakers about how interactions between specific groups or even species of microbes can have large effects on their growth and behavior. One of the most striking findings was the specificity, both spatially and temporally, of the bacterial communities associated with eukaryotic phytoplankton. Thalassiosira rotula cells isolated from water samples from across the globe possessed distinct bacterial assemblages depending on location, found Olivia Marjorie Ahern. Another study by Hanna Farnelid, focusing on one location but taking samples across time, found evidence for species-specific functional associations between picoeukaryotes and bacteria. Laboratory coculturing experiments by Marilou Sison-Magnus showed that as the number of cocultured bacteria in a diatom culture increase, diatom growth rate also increases—but only when certain combinations of bacteria are present. In contrast, other combinations of bacteria enhanced production of domoic acid, a toxin associated with Harmful Algal Blooms (HABs). The distinct phycospheres created by these microbial relationships, the speakers pointed out, could impact processes from primary production up to ecosystem-level energy transfers. New ways to observe and quantify these microbial relationships were also a focus during this session. For example, a novel method of determining intracellular B vitamin concentrations has allowed Chris Suffridge to examine which members of the microbial community are consuming these essential vitamins. He found that bacteria, not phytoplankton, were the dominant consumers of B12, while the community was likely synthesizing B1. Furthermore, the addition of each vitamin had a distinct effect on the microbial community, indicating that shifting B-vitamin concentrations impact not only growth rates but also community composition. Another novel method presented during this session was a microfluidic technique developed by Bennett Lambert and his lab that will allow scientists to create in situ bacterial chemotaxis assays. Bacteria that respond to microplumes of chemoattractants are caught in the device's wells, and these samples are assessed using flow cytometry and molecular techniques. This technique can be used to investigate the chemical preferences of marine microbes at the microscale, rather than using bulk parameters that merely record the sum of microbial interactions. After hearing about microbial relationships for much of the session, one question remained: why are these associations so specific? Ecology-based studies delved into the basis behind these interactions, demonstrating again how varied they are. Lauren Marie Seyler demonstrated that the basis for the coexistence of bacteria and archaea in the deep sea may be related both to resource partitioning and selective predation, while a study of how grazers impact blooms of Synechococcus in the Gulf of Maine by Peter Dylan Countway found that certain types of protist grazers were likely to respond to Synechococcus blooms and that these grazers appear to exert a strong degree of control on the abundance and duration of the annual bloom. Focusing less on the microscopic, Nicole Lopanik examined variations in symbiosis between the marine bryozoan Bugula neritina and its bacterial symbiont, finding that high latitude, symbiont-less bryozoans likely do without their symbiont because the benefits of the relationship, namely protection from predation, aren't as necessary in high-latitude environments because of lower inherent predation pressure. While this session helped us all to better decode the ocean's microbial relationships, it also highlighted how much we still have to learn. With the potential for impacts on both micro- and macroscale ecological and biochemical processes, there's no doubt we'll be seeing more on this topic at future ASLO meetings.