Description

Marinobacter is a ubiquitous, motile, halophilic to halotolerant, marine bacteria commonly found in the core microbiome of phytoplankton such as diatoms and dinoflagellates. These phytoplankton are commonly implicated in harmful algal blooms. It has been proposed that Marinobacter may be a keystone taxon that regulates the phytoplankton host through siderophore production in exchange for carbon source nutrients provided by the phytoplankton. To ensure colonization by beneficial bacteria, the phytoplankton cells create a concentrated chemical environment, or “phycosphere”, surrounding the cell to encourage attachment of beneficial bacteria and suppress or inhibit growth of unwanted ones. Similarly, the bacterial community can also regulate each other through a similar process to reduce resource and space competition. In a previous study, the Carrano lab described a phenomenon observed between two “sibling” bacterial colonies of Marinobacter where the colonies were able to prevent territory overlap through non-lethal chemical communication that inhibits motility rather than through standard quorum sensing mechanisms. In this study, we set out to discover the small molecule causing this phenomenon using qualitative, untargeted metabolomics to analyze the media extracted from the agar at various zones, including the inhibition zone. We were able to identify and validate seven candidate molecules, but only one proved to be effective at limiting motility through motility assays. Then using targeted analysis, we quantified the compound across the various sampling zones using the standard addition method to confirm that the compound is present at highest concentrations within the inhibition zone.