In bacterial cells, bidirectional replication of the circular chromosome is 
initiated from a single origin (oriC) and terminates in an antipodal terminus 
region such that movement of the pair of replication forks is largely 
codirectional with transcription. The terminus region is flanked by discrete Ter 
sequences that act as polar, or direction-dependent, arrest sites for fork 
progression. Alternative oriC-independent modes of replication initiation are 
possible, one of which is constitutive stable DNA replication (cSDR) from 
transcription-associated RNA-DNA hybrids or R-loops. Here, I discuss the 
distinctive attributes of fork progression and termination associated with 
different modes of bacterial replication initiation. Two hypothetical models are 
proposed: that head-on collisions between pairs of replication forks, which are 
a feature of replication termination in all kingdoms of life, provoke bilateral 
fork reversal reactions; and that cSDR is characterized by existence of distinct 
subpopulations in bacterial cultures and a widespread distribution of origins in 
the genome, each with a small firing potential. Since R-loops are known to exist 
in eukaryotic cells and to inflict genome damage in G1 phase, it is possible 
that cSDR-like events promote aberrant replication initiation even in 
eukaryotes.