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The role of phytoplankton-bacteria interactions in marine microbial ecology

The role of phytoplankton-bacteria interactions in marine microbial ecology. Katy Davis Marine Science & Conservation. Courses. Background. From Simon et al. (1997). From Cho & Azam (1990). Bacteria-phytoplankton interactions. Modified from (Cole 1982). Specific Aims.

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The role of phytoplankton-bacteria interactions in marine microbial ecology

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  1. The role of phytoplankton-bacteria interactions in marine microbial ecology Katy Davis Marine Science & Conservation

  2. Courses

  3. Background From Simon et al. (1997) From Cho & Azam (1990)

  4. Bacteria-phytoplankton interactions Modified from (Cole 1982)

  5. SpecificAims • Aim1)To quantify the importance of motility in bacterial interactions with marine phytoplankton. • Aim 2) To understand the processes that mediate phytoplankton-bacteria coupling in marine systems.

  6. Aim 1 Question 1): Is there a competitive advantage of chemotaxis and motility for heterotrophic marine bacteria in co-culture with phytoplankton, given the high energetic and metabolic costs of motility? From Stocker (2012)

  7. T. rotulacell Tracks of motile bacteria around T. rotulacell Q1: motility advantage? Aim 1 (Photos: N. Vahora)

  8. Generate motility mutant using transposon mutagenesis Grow non-motile mutant and wild-type motile strain in co-culture with diatom. Compare growth rates Q1: motility advantage? Aim 1

  9. PREDICTIONS • Wild-type will have higher growth rate at low algal densities • Advantage depends on distribution of resources From Stocker and Seymour (2012) Q1: motility advantage? Aim 1

  10. Aim 2 Question 1) How does nutrient limitation affect the relationship between a phytoplankton-heterotroph pair, as evidenced by transcriptomic changes? Question 2) Do the specific strains of heterotrophic bacteria co-cultured with the toxic bloom-forming alga, Kareniabrevis, affect the growth rate and toxins produced by K. brevissince this dinoflagellate cannot be grown axenically?

  11. Compare co-culture gene expression to: • P-limited conditions • Axenic controls • P-limited axenic controls From Westermann et al. (2012) Q1: interactions from gene expression? Aim 2

  12. PREDICTIONS • Nutrient-replete conditions • Cross-talk between organisms • Synthesis of exchanged metabolites • P-limited conditions • Shift from mutualism to antagonism • Diatoms: communication and defense • Bacteria:  nutrient and carbon acquisition Q1: INTERACTIONS FROM GENE EXPRESSION? AIM 2

  13. Isolate heterotrophic bacteria Make 16S rRNA gene libraries Transplant isolates among K. breviscultures Measure effect on K. brevisgrowth rates and cellular toxin content Q2: INFLUENCE OF SPECIFIC BACTERIA ON ALGAE IN CULTURE? AIM 2

  14. PREDICTIONS • Additions of specific microbial taxa will explain some of the observed variations in growth rates and cellular toxin content among strains • Bacterial abundance and community composition for each clone will be: • Taxonomically distinct • Regulated Q2: INFLUENCE OF SPECIFIC BACTERIA ON ALGAE IN CULTURE? AIM 2

  15. Summary • Three aspects of algal-bacterial associations will be explored: • Motility • Gene Expression • Specificity of associations and their influence on algal physiology

  16. Timeline

  17. Acknowledgments Committee Members: Dana Hunt Zackary Johnson Wayne Litaker Amy Schmid Brian Silliman Chris Ward Charmaine Yung Tatiana Rynearson Pat Tester RanceHardison

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