Epulopiscium spp. are the largest known heterotrophic bacteria. Individual, cigar-shaped cells can reach lengths in excess of 600 µm; large enough to be seen with the naked eye. In terms of cell volume, Epulopiscium can be as much as a million times larger than a bacterium the size of Escherichia coli. Another unusual feature of these big bacteria is the manner in which they reproduce. While most bacteria undergo binary fission -- growing to about twice their starting size and dividing into two equivalent daughter cells -- an Epulopiscium cell can produce multiple offspring intracellularly. These internal offspring grow inside the mother cell until they completely fill the mother cell cytoplasm. The offspring cells eventually burst through the mother cell envelope and are released. Morphological and phylogenetic evidence suggests that this novel form of reproduction evolved from endospore formation. The image below shows a particularly large Epulopiscium cell that contains two large offspring.
"Epulopiscium" means "guest at a banquet of a fish". So named because Epulopiscium spp. (including Epulopiscium fishelsoni) live in the intestinal tract of certain species of tropical marine surgeonfish. Based on genome sequence analyses, these intestinal symbionts aid the breakdown and digestion of algae consumed by their surgeonfish host.
Research in the Angert lab focuses on several aspects of Epulopiscium biology.
- Characterizing cellular modifications that support large cell size.
- Identifying molecular mechanisms involved in intracellular offspring formation and development.
- Determining how reproductive strategy impacts the symbiotic relationship of intestinal bacteria and their vertebrate host.
We have developed a number of approaches to study Epulopiscium spp. and relatives in their natural environments. Current research projects use comparative genomics, phylogenetics, cell biological and microbiological methods to study these exceptional microorganisms. In addition, we have on-going collaborative projects describing the ecology and diversity of gastrointestinal microbial symbionts of fish and their impact on fish health and nutrition.