Marine microbial biogeography from microscopic to global scales: ecology of the diatom Pseudo-nitzschia

Abstract

Members of the marine diatom genus Pseudo-nitzschia are globally distributed, biologically productive, remarkably diverse, and responsible for Harmful Algal Blooms (HABs) through the production of the neurotoxin, domoic acid. This dissertation explores three major dimensions of life which are important to the biogeography and toxigenicity of Pseudo-nitzschia, employing methods of culturing, genetic fragment analysis techniques, collection of standard oceanographic data, and in silico analysis of publicly available DNA sequences. First, we report species-specific bacterial communities associated with Pseudo-nitzschia cultures; furthermore, these communities varied according to culture toxigenicity. Second, Pseudo-nitzschia communities were responsible for moderate DA levels in the northern Benguela Upwelling Zone, potentially caused by species previously reported as very weakly toxigenic. Throughout the South Atlantic Ocean, novel and known Pseudo-nitzschia types were detected, with communities exhibiting biogeographic patterns that varied with abiotic ocean conditions. Third, newly constructed nuclear- and chloroplast-based phylogenies suggest the existence of two major Pseudo-nitzschia clades, which exhibit similar morphological and physiological characters. Together, these findings describe Pseudo-nitzschia as an organism that is tightly coupled with its biotic and abiotic surroundings.