Two canonically aerobic foraminifera express distinct peroxisomal and mitochondrial metabolisms

Abstract

Certain benthic foraminifera are known to thrive in marine sediments with low oxygen or even without detectable oxygen. Potential survival avenues used by these supposedly aerobic protists include fermentation and anaerobic respiration, although details on their adaptive mechanisms remain somewhat elusive. To better understand the metabolic versatility of foraminifera, we studied two benthic species that thrive in oxygen-depleted marine sediments. Here we detail, via transcriptomics and metatranscriptomics, differential gene expression of Nonionella stella and Bolivina argentea, collected from Santa Barbara Basin, California, USA, in response to varied oxygenation and chemical amendments. Organelle-specific metabolic reconstructions revealed that these two species utilize adaptable mitochondrial and peroxisomal metabolism that reflect their differing lifestyles. N. stella, most abundant in anoxia and characterized by the lack of food vacuoles and the abundance of intracellular lipid droplets, was predicted to couple the putative peroxisomal beta-oxidation and glyoxylate cycle with a versatile electron transport system and a partial TCA cycle running in the reductive direction. In contrast, B. argentea, most abundant in hypoxia and contains food vacuoles, was predicted to utilize the putative peroxisomal gluconeogenesis and a full TCA cycle but lacks the expression of key beta-oxidation and glyoxylate cycle genes. These metabolic adaptations likely confer ecological success while encountering deoxygenation and illuminate the importance of metabolic modifications and interactions between mitochondria and peroxisomes in protists. ImportanceForaminiferan protists are nearly ubiquitous in todays oceans and likely were major components of the Neoproterozoic protistan community. While largely considered aerobic, certain foraminifera demonstrate surprising adaptability to hypoxia and anoxia, contributing to biogeochemical cycling in benthic environments. The analyses of Rhizarian adaptive metabolism set the stage for studying other microeukaryotes under increasing ocean deoxygenation. Revealing the metabolic roles of foraminifera in anaerobic biogeochemical cycling should spur reassessments of existing paleoecological datasets as well as new perspectives on the metabolic evolution of eukaryotic cells.