Metabolic lifestyle and energy conservation tricks of giant, symbiotic bacteria – the special case of Epulopiscium

Research in the last few decades has brought considerable advances in our understanding of the biology of several giant bacteria that seem to bypass the diffusional limitations of unicellular prokaryotes lacking specialized intracellular transport mechanisms, including two marine sulfur-oxidizing species (Beggiatoa and Thiomargarita) and the gut symbiont of herbivorous surgeonfishes, Epulopiscium fishelsonii. The latter bacteria are morphologically diverse, sometimes longer than 600 μm, and extraordinarily polyploidic, carrying as much as 600,000 genome copies per cell. Unlike other bacteria, they form multiple intracellular offspring in a circadian reproductive cycle that is synchronized with the feeding behaviour of their hosts. However, very little is known about the metabolic traits of Epulopiscium and their potential roles in the digestive process. In this talk, I will provide genomic evidence that links metabolism, lifestyle, and mechanisms for energy-conservation in Epulopiscium and advances our understanding of their potential physiological roles in their symbiosis with surgeonfishes.