The Metabolic Innovations of Benthic Protists in Response to Anoxia: Foraminifera as Models

The overall goal of this project is to advance our understanding of the evolution of eukaryotic life on Earth by examining extant eukaryotic taxa that live in an analog environment for early Earth conditions, and how symbioses and metabolic pathways used within these holobionts permit inhabitation by eukaryotes of a wide variety of environmental conditions, including sulfidic, anoxic, and hypoxic sediment pore waters. Foraminifera (hereafter “forams”) are a successful and diverse protistan group that evolved in the Precambrian. Certain foram species thrive near anoxia; others in euxinia (sulfide enriched anoxia). Most of these have the ability to denitrify, an anaerobic respiration process, although debate exists whether this is bona fide eukaryotic denitrification or from prokaryotic associates. Three species of SBB forams will be used as models because each has different cellular ultrastructure, where two have endobionts of different morphologies; the third is kleptoplastidic (harboring chloroplasts) despite inhabiting sediments far below the classic photic zone. We are: 1) assessing the transcriptional activities of target holobionts in their natural habitat using specimens preserved in situ on the seafloor; 2) obtaining draft genomes of target foraminifera and their associated symbionts to elucidate metabolic potential of partners; and 3) assessing metabolic activities and potential exchanges between holobiont partners that underpin holobiont survival under anoxia, among other things.