The boundaries of the blocks are thought Selleck Entinostat to be hotspots of recombination and insertion. For example, the major histocompatibility complex (MHC) is located between such blocks [29]. Our study sheds light on the hotspots in genomes for GI insertion using a large scale comparative genomic method. Our results suggest that GIs are likely to be inserted at the block boundaries of genomes of bacteria and other microbes, and sGCSs in these genomes are common separation spots for such blocks. Via a phylogenetic

analysis of each pGI and its homologues, we obtained the evolutionary distance for each pair of homologous pGIs. After studying the correlation between Ds and De, we found that they are positively correlated in regions closer to sGCSs (0-25%), while the correlation is reversed in more distal regions (25 – 50%). The turning point is near 25% region for geomes with two sGCSs. The mechanism underlying this PFT�� phenomenon is currently unclear but may be caused by genomic rearrangements or deletions. In human pathogens, many PAIs are found in GIs, such as VSP I and II in V. cholerae. However, generally speaking, PAIs and GIs refer to different genomic features. On the one hand, PAIs are sometimes evaluated by

sequence similarity in other species, and these PAIs do not display abnormal GC content. Additionally, not all GIs are associated with pathogens. For example, in E. coli CTF073, none of the four abnormal GC content regions matches PAIs. These PAIs are different selleck from typical PAIs due to

special genomic rearrangement mechanisms. According to our observations, only laterally transferred GIs and newly acquired GIs are found near sGCSs. Notably, these types of horizontally transferred GIs were discovered in recent emerging infectious diseases and proven to enhance virulence or adaption of such strains [21, 30]. Therefore, GIs are of great importance in revealing the mechanisms of certain epidemic diseases. From Celecoxib the observation that GIs are likely to be inserted at genomic block boundaries, we propose that important virulence factors, which are associated with the outbreaks of many common diseases and/or enhanced virulence can be found near sGCSs. Conclusion In this study, in order to do a large scale study on the properties of genomic island, we used 1090 bacterial chromosomes (from 1009 bacterial species) as samples and 83 chromosomes (from 79 archaeal) as controls and separated them into three groups (sCGSs < = 2; 4 < = sCGSs < = 8; sCGSs > = 10) according to the number sCGSs. Interestingly, most of bacteria genomes contain less than 8 sCGSs, while archaeal genomes often contain more than 8 sCGSs. We then searched the genomic sequence for GIs by identifying the genomic segments with GC contents significantly different from the mean value of the genome and detected 20,541 GIs.