Growth & Ingestion Rate of Ochromonas CCMP 1391 Under Nutrient Limitation

Protistan plankton were historically classified as either strict phototrophs or heterotrophs; we now understand that mixotrophs - organisms that can use multiple trophic modes for nutrient acquisition - are far more prevalent than previously thought. This flexibility between trophic modes may be induced by oligotrophic conditions, but more research is needed to understand the impact of nutrient limitation with the onset of, or increase in, mixotrophic prey ingestion. One mixotroph, Ochromonas sp. (CCMP 1391), is a constitutive mixotroph and a facultative phagotroph. We evaluated the growth and ingestion rates of Ochromonas under nutrient-limited conditions to test the hypothesis that Ochromonas would overcome nutrient limitation by phagotrophically ingesting prokaryotic or eukaryotic prey.  To do so, xenic Ochromonas cultures were grown in filtered seawater (FSW)- and artificial seawater (ASW)-based L1 media, under nutrient-replete, reduced nitrogen (-N), and reduced phosphorus (-P) conditions. Nutrient limitation led to diminished Ochromonas growth. The impact of nutrient limitation on the ingestion of algal prey was assessed by growing Ochromonas with the prey species Micromonas and Green fluorescent protein E. coli (in separate trials), while monitoring ingestion rates. While Ochromonas was ingesting the Micromonas and GFP E. coli, we did not find significant differences between nitrogen limitation and the control (control: μ = 8 d-1, -N: μ =5 d-1). Similarly, light limitation did not induce a measurably different ingestion rate relative to the control (light: μ = 2 d-1).  Ingestion rates were lower than in previous studies, suggesting that Ochromonas in our experiments could have been feeding on unlabeled prey, and that further investigation is needed to determine a potential impact of prey preference on ingestion rate.

Presentation Preference: Oral

Primary Presenter: Alejandro Mapula, Texas A&M University at Galveston (alexdmapula@gmail.com)

Authors:

Alejandro Mapula, Texas A&M University at Galveston  (admapula21@tamu.edu)

Isaac Miller, Bigelow Laboratory for Ocean Science  (imiller@bigelow.org)

Laura Lubelczyk, Bigelow Laboratory for Ocean Science  (llubelczyk@bigelow.org)

Nicole Millette, Virginia Institute of Marine Science  (nmillette@vims.edu)

Karen Stamieszkin, Bigelow Laboratory for Ocean Sciences  (kstamieszkin@bigelow.org)

Nicole Poulton, Bigelow Laboratory for Ocean Science  (npoulton@bigelow.org)