Intracellular pathogens: living in an extreme environment

摘要: The phylogenetic tree segregates into three major groups, which probably descended from a common ancestor: the bacteria, archaea, and eucarya (1–3). While bacteria archaea lack true nucleus intracellular organelles, possess these. origin of ancestor remains elusive, but it emerged about 4 billion years ago. started life 3.5 ago eukaryotes 1.75 thereafter. Sometime in between appeared. Eukaryotes began as unicellular organisms soon also developed multicellular forms. Bacteria had sufficient time to exploit all niches abiotic environment, ranging ice cold glacial lakes fiery geysers – highest mountain peaks deepest sea beds. They quickly forms mutualism by forming colonies composed mixed populations. With evolution eucarya, new environments could be exploited. Today prokaryotes are most prevalent form on earth, making up majority our biomass. It has been estimated that more than 10 prokaryotic live globe. Thus, far eucarya. Even human beings comprise cells mammalian cells, range order mostly concentrated intestinal system (4–7).