Open Problem: Multiple Replication Origins in a Bacterial Genome

Biologists long believed that each bacterial chromosome has only one ori. Wang et al., 2011 genetically modified E. coli by inserting a synthetic ori a million nucleotides away from the bacterium’s known ori. To their surprise, E. coli continued business as usual, starting replication at both locations!

Existence of bacteria having multiple oris

Following the publication of this paper, the search for naturally occurring bacteria with multiple oris immediately started. In 2012, Xia raised doubts about the “single ori” postulate and gave examples of bacteria with highly unusual skews. In fact, having more than one ori makes sense in the light of evolution: if the genome is long and replication is slow, then multiple replication origins would decrease the amount of time that the bacterium must spend replicating its DNA.

For example, Wigglesworthia glossinidia, a symbiotic bacterium living in the intestines of tsetse flies, has the atypical skew diagram shown in the figure given below. Since this diagram has at least two pronounced local minima, Xia argued that this bacterium may have two or more ori regions.