Date of Award
Master of Science
Gladys Alexandre-Jouline, Steven Wilhelm
The Roseobacter clade is an abundant and biogeochemically relevant group of marine bacteria. Physiological and ecological traits identified in specific representatives of the clade are often universally attributed to all Roseobacter group members, however, culture-dependent studies utilizing phylogenetically distinct members are rare. Other attributes often associated with this clade include motility, biofilm formation and surface attachment, chemotaxis and quorum sensing. This study compared a collection of 13 diverse Roseobacter strains both pheno- and genotypically on the basis of these traits. Motility was determined for seven previously uncharacterized strains, with five of the strains demonstrating motility. Microscopic analysis using both phase contrast and transmission electron microscopy supported this finding. A crystal violet assay was used to assess biofilm formation on plastic and glass surfaces with a range of surface properties and yielded a wide array of phenotypic responses. Taking into account the variety of surface types and media types tested approximately half (54%) of the strains showed pronounced biofilm formation and all motile strains were capable of forming biofilms. Degenerate primer sets were designed to probe strains for which no genome sequence is currently available for genes involved in flagellar synthesis and chemotaxis. Two strains that demonstrated no signs of motility in the laboratory were found to possess a necessary gene for flagellar formation and a flagellar-associated chemotaxis gene. Genome analysis including other sequenced Roseobacter strains revealed that flagellar, chemotaxis and quorum sensing operons are abundant in members of this lineage, with 89% possessing flagellar and chemotaxis operons and 78% possessing genes believed to be involved in quorum sensing. This study underscores the diversity of this clade and emphasizes the difficulty of assigning phenotypic capabilities to all lineage members.
Slightom, Rachael N., "Characterization of Motility and Surface Attachment in Thirteen Members of the Roseobacter Clade. " Master's Thesis, University of Tennessee, 2008.