Diversity of the Marine Cyanobacterium: Characterization of the Woods Hole Culture Collection and Quantification of Field Populations
Annette Hynes, Ph.D., 2009
Scott Doney, John Waterbury, Advisors
Trichodesmium is a colonial, N2-fixing cyanobacterium found in tropical oceans. Species of Trichodesmium are genetically similar, but several species coexist. In order to coexist, species may occupy different niche spaces through differential utilization of resources and responses to physical characteristics. To investigate niche differentiation in Trichodesmium, I characterized cultured strains of Trichodesmium, identified and enumerated Trichodesmium clades in the field, and investigated P stress and N2 fixation in field populations. Species of Trichodesmium group into two morphologically diverse clades that are coherent with respect to pigment composition: clade I (Trichodesmium erythraeum and Trichodesmium contortum), and clade II (Trichodesmium thiebautii, Trichodesmium tenue, Trichodesmium hildebrandtii, and Trichodesmium pelagicum). I developed a quantitative polymerase chain reaction (qPCR) method to distinguish between these clades and applied it to field populations in the Atlantic and Pacific. Clade II Trichodesmium spp. were more prominent than clade I in the open ocean. Neither clade correlated with nutrients, but clade I had wider temperature and depth distributions than clade II. Trichodesmium populations in the North Atlantic were more P stressed and had higher N2 fixation rates than the Pacific. Unraveling differences among Trichodesmium spp. enables us to understand their coexistence and factors controlling global N2 fixation.