The genetic content of most bacteria is inherited in a single chromosome. However, bacteria of the Vibrionaceae family encode their genetic information on two separate chromosomes. While studying the two-chromosome system in Vibrio, three natural single-chromosome Vibrio strains (NSCV) were discovered. In these strains chromosomes are stably fused and do not revert into the two-chromosomal state. The genetic mechanism underlying the unidirectional chromosomal fusion events and how the fusion is stably maintained remain unknown.

Recombination between homologous sequences in the chromosome of NSCV strains can potentially lead to the separation of the fused chromosomes. To test whether NSCV strains are still able to perform homologous recombination, we treated NSCVs with UV-irradiation and Mitomycin C. These agents cause DNA double strand breaks, which are repaired via homologous recombination. Our results show that NSCV strains overcome this treatment indicating recombination proficiency. Although proven to be capable of homologous recombination, pulsed-field gel electrophoresis detected no division of the fused chromosome in NSCV clones irradiated with elevated UV doses.

To find more natural occurring examples of fused chromosomes to establish general "fusion rules", we screened 180 strains of the Vibrionaceae via PacBio sequencing. The analysis of new NSCV genomes could reveal specific genetic characteristics which might explain the locked single-chromosomal state.