Bacterial Phenotypes of the Equatorial Pacific in the Presence of Different Phytoplankton Metabolites

Abstract

Metabolites are compounds released by phytoplankton, and are major sources of carbon and other essential nutrients for heterotrophic bacteria living in the pelagic ocean, which form the base of marine food webs via the recycling of nutrients. The goal of my experiment was to determine how the prevalence of different phytoplankton metabolites can influence heterotrophic bacterial community composition, with a focus on the equatorial Pacific region. My hypothesis was that different bacteria would show increased growth on media enriched with certain metabolites, and decreased growth on other media enriched with other metabolites. This was achieved by collecting seawater samples from three locations along a transect of the equator, which were then concentrated and plated on agar plates enriched with some of the more common phytoplankton metabolites: Glycine Betaine (GBT), Dimethylsulfoniopropionate (DMSP), Spermidine, Glucosamine, and Sucrose. A complete nutrient option (1/2 YTSS) was used as a control. These plates were assessed for bacterial growth via Colony Forming Units (CFU’s) after a 5-day incubation period. My results showed a northward trend of increasing phenotypic diversity, as well as higher numbers of CFU’s in locations north of the equator. There was also significant variation amongst the different metabolites in regard to the species of bacteria (based on colony phenotype) that grew and the number of CFU’s present. There were some consistent phenotypes across all media types. Based on these results, the metabolites present in the water column may be an important determining factor in the composition of the heterotrophic bacterial community.