Chromosomes of bacteria

Abstract

The emergence of bacteria is nearly synonymous with the origin of life on earth. For this reason bacterial chromosomes are considered if not the most primitive, quite close to that state. But is it really so? Bacteria have had 3.5 billion years at their disposal to evolve and during this time they have been able to populate the most adverse environments, living at temperatures above 100 °C and surviving on oil deposits. The chromosomes present in today’s living bacteria may differ appreciably from those found in the first prokaryotes. Several mechanisms exist in their chromosomes that indicate an advanced condition, such as the presence of two types of chromosomes. The main circular large chromosome contains most genes. Minor additional chromosomes, called plasmids or episomes, have a few additional genes and replicate autonomously. Both types consist of DNA.