Abstract Detail

Symbioses: Plant, Animal, and Microbe Interactions

Paasch, Amber [1], Kim, Eunsoo [2].

Phagocytosis of bacteria provides the mixotrophic green alga Cymbomonas tetramitiformis (Prasinophyceae) with a competitive advantage in phosphate-limited environments.

Green algae and land plants, together constituting the lineage Chloroplastida, possess a photosynthetic “bacterium” that was captured ~1.2 billion years ago. This bacterium was retained by the ancestors of green algae and after rounds of replication and gene loss, the bacterium evolved into an organelle, the first chloroplast. The method of ingestion of the bacterium, called phagocytosis, was assumed to be lost in the Chloroplastida due to the success of photosynthesis. Recently, however, a marine green alga, Cymbomonas tetramitiformis, was definitively confirmed to ingest bacteria utilizing a unique permanent acidic vacuole and a feeding duct. This feeding apparatus may be plesiomorphic for the Chloroplastida and hence may have been the method of chloroplast acquisition. While land plants and many green algae have lost this feeding capacity, it is not clear what environmental conditions provide evolutionary pressure to retain a dual mode of nutrition (feeding and photosynthesis). This study tested the hypothesis that limitation of resources facilitates eating of bacteria in mixotrophic green algae. To identify environmental drivers of phagocytosis, C. tetramitiformis was grown in nutrient limited media then supplemented with bacteria as a rescue. Bacteria only rescued C. tetramitiformis growth under phosphate-limited conditions, but not under nitrogen or light-limited regimes. This suggests that bacteria provide C. tetramitiformis with phosphate supplementation. Utilizing the C. tetramitiformis genome that our lab has recently assembled, sets of genes that are involved in C, N, and P metabolic pathways were mined and compared to the growth experiment data. The results provide preliminary evidence that retention of bacteria ingestion in green algae is due to a competitive advantage in phosphate-limited environments.

1 - American Museum of Natural History, Richard Gilder Graduate School, 79th St. at Central Park West, 5th Floor, New York, NY, 10024, USA
2 - American Museum of Natural History, Invertebrate Zoology, 79th St. at Central Park West, 5th Floor, New York, NY, 10024, USA

Keywords:
algae
endosymbiosis
nutrients
physiology.

Presentation Type: Oral Paper:Papers for Topics
Session: 51
Location: Salon 5/The Shaw Conference Centre
Date: Tuesday, July 28th, 2015
Time: 2:00 PM
Number: 51003
Abstract ID:1299
Candidate for Awards:None