Biological control

The work of this dissertation examined the secondary metabolites of several blooms of the marine cyanobacterium Lyngbya collected in Guam and Florida with an emphasis on the isolation and structure elucidation of novel biologically active compounds. The introduction in Chapter One provides a brief history of marine natural products, a description of cyanobacteria and a summary of peptides isolated from Lyngbya collected in the Caribbean. In Chapter Two, a bioassay-guided fractionation of a Floridian collection of Lyngbya polychroa led to the isolation and structural determination of the cytotoxin desacetylmicrocolin B and the known compounds microcolins A and B. The structures were established by nuclear magnetic resonance (NMR) spectroscopic analysis. All three compounds inhibited the growth of cancer cell lines HT-29 and IMR-32 at nanomolar concentrations. Microcolins A and B were found to have little activity in the ecological assay against the marine fungus Dendryphiella salina. Chapter Three describes the isolation and structure elucidation of the glycosidic, acyl proline derivative tumonoic acid J from a sample Lyngbya sp. collected in Guam. The planar structure was determined by 1D and 2D NMR spectroscopy in conjunction with high resolution-mass spectrometry (HR-MS) data. Tumonoic acid J showed moderate activity in the ecological assay against the marine fungus D. salina. In Chapter Four, NMR-guided fractionation of a Floridian sample of Lyngbya majuscula led to the isolation of two novel cyclic peptides porpoisamides A and B. The planar structures were determined by 1D and 2D NMR spectroscopy with HR-MS data. The absolute configurations of these two compounds were defined through chiral chromatographic methods and derivatization techniques.

Extensive blooms of the marine cyanobacterium Lyngbya majuscula occurred during 2006 in Halodule wrightii seagrass beds. We examined the effects of L. majuscula blooms on seagrass by removal treatments and assessed if this was primarily an effect of shading by conducting artificial shade treatments. We tested the effects of L. majuscula removal and artificial shading on fifty individual 0.25 m2 experimental seagrass plots infested with L. majuscula in a fully crossed, two-way experiment. Measurements included blade elongation, biomass, and stem density. Blade lengths of H. wrightii were significantly increased by the presence of artificial shading and L. majuscula. L. majuscula removal resulted in increased below ground biomass in shaded plots, suggesting an increase in stores, when possible, for accelerated recovery following a shading event. Adverse L. majuscula effects occurred after declines in bloom biomass indicating that L. majuscula can have a prolonged negative effect on H. wrightii production.