CELLULAR ULTRASTRUCTURE OF BENTHIC FORAMINIFERA FROM DEEP-WATER HYDROCARBON SEEPS

Benthic foraminifera are important geomicrobiological tools because they are microscopic eukaryotes with fossilizable shells (tests). The foraminiferal fossil record is long, with (debated) evidence indicative of a Precambrian origin. Their fossilized remains have a multitude of uses such as identifying changes in environment, sea level, and pollution events. Although they have classically been considered aerobes, some species inhabit “extreme” habitats, with certain species capable of performing complete denitrification; examples of extreme habitats include hydrocarbon/methane seeps and anoxic sediments of silled basins. Prior ultrastructural analyses have described foraminiferal adaptations in such extreme environmental conditions including peroxisome proliferation, symbionts, kleptoplasty, and mitochondria-test pore associations. These foundational observations raised questions about gene expression—recent research revealed that certain foraminifera are capable of more than one type of anaerobic metabolism. Despite these examples, there is still much to be learned about the mechanisms allowing foraminifera to occupy these seemingly extreme environments.

A first step to establish how foraminifera can live in such extreme environments is by analyzing their cellular ultrastructure via Transmission Electron Microscopy (TEM). There are limited studies of the ultrastructure of hydrocarbon seep foraminifera. Cytological observations of specimens collected from Thioploca mats (colonial filamentous sulfur oxidizing bacterium) in deep-water hydrocarbon seeps in the Gulf of Mexico will be presented. This is the first ultrastructural analysis of living allogromids, a basal group of non-calcareous foraminifera, from hydrocarbon seeps. Observations from saccaminid foraminifera, another early evolving non-calcareous form, will also be presented. Given foraminifera are important paleoenvironmental indicators, it is important to know the extent of their physiological abilities to better inform paleooceanographic and paleoecologic reconstructions. This contribution will greatly augment understanding of extremophile foraminifera, adding to the burgeoning understanding of microeukaryote/microfossil diversity and adaptations.