In the belly of the whale: endobionts inhabit the world's largest bacteria

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

Mitochondria and chloroplasts, the organelles that provide energy to the eukaryotic cell, are thought to have evolved more than two billion years ago from symbiotic bacteria that lived within a microbe. Despite their potential to help in the understanding of eukaryote evolution, examples of bacteria that host other bacteria are very rare. The principal investigators recently discovered a population of giant bacteria that host dense populations of bacteria within their cells. The investigators will study the community of bacteria associated with the giant bacteria, determine how certain bacteria enter the host cells, and explore the interactions among the intracellular bacteria and the giant host cell. This system provides a unique opportunity to gain an understanding of this host bacterium-bacteria symbioses. In addition to exploring basic aspects of eukaryotic evolution and microbial interactions, the investigators will provide field and laboratory experiences for U.S. military veteran students, U.S. high school students, and students from Namibia, bringing the students together in a novel exchange program. This international partnership will not only help train U.S. student veterans in STEM fields, and high school students from underrepresented groups, but also help to expand the research capabilities of sub-Saharan Africa by training students in cutting-edge approaches to studying fundamental cell processes. Endosymbiotic relationships involving prokaryotic host cells and other prokaryotes are extremely rare and not well understood. The investigators recently discovered a population of metabolically active giant sulfur bacteria cells, Thiomargarita spp., that contain dense populations of intracellular bacteria. Some of these bacteria are related to known animal endosymbionts but the structure and ecology of these intracellular bacterial communities is still incomplete. To better understand the host bacterium-bacteria symbioses, the investigators are (1) investigating the microbial community structure associated with different phylotypes of Thiomargarita spp., 2) identifying the potential mechanism(s) by which cells enter Thiomargarita spp., and 3) studying ecological and physiological interactions between the endobiont bacteria and Thiomargarita spp. In order to investigate potential interactions between host Thiomargarita spp. cells and their endobionts, as well as to characterize the community compositions, a set of diverse techniques, such as metagenomics, metatranscriptomics, and fluorescence in situ hybridization, are being employed. In addition, infection challenge experiments are being performed to elucidate the potential mechanisms by which the endobiont(s) becomes internalized within the host cell. This research has the potential to provide insights into eukaryotic evolution and the interactions that underlie the host prokaryote-endosymbiotic prokaryotes symbioses. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.